Two dozen referees were needed to get the fine distinction between Undertaker and Triple H's Power Levelsjust right.
A simplistic ranking system in which Power Levels are something other than specific measurements, usually in the form of broad categories.
Much like Character Tiers, this discussion centers on which character(s) are the most powerful. Unlike Character Tiers this happens inside the show/game and does not get deeply involved in the factors affecting the debate.
Inevitably, any series with this kind of grading system will be subject to Rank Inflation, sometimes to ridiculous levels just to keep up with things like the Sorting Algorithm of Evil. In the end the heroes will always be as Strong as They Need to Be, so all this rigamarole can get beside the point.
Compare Awesomeness Meter. Distinct from Power Levels which are specific measurements, this trope deals with less specific things. For example, if a character was rated at "709 in Ki Manipulation", that's Power Levels. But if they were rated a "Class 2 (of 5) in Ki Manipulation" that's this trope.
Common scales include:
Latin Letters (commonly A through D, usually adding S above A if it gets into Rank Inflation territory, followed by even more S-es if that isn't enough.)
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Anime & Manga
The Stands from JoJo's Bizarre Adventure are given letter grades in several categories such as power, speed, precision, and so on. These really don't mean much, as the overall effectiveness of a Stand isn't how powerful it is, but how cleverly it can be used.
That factor is (presumably) indicated by "Learning," which seems to indicate how well the Stand user knows the limits and capabilities of his/her/its Stand.
Magical Girl Lyrical Nanoha has the Mage Ranks used by the Time-Space Administration Bureau for those under them. The TSAB has a logical way of assigning ranks. They have Rank Promotion tests, and you advance to that rank if you pass, making you eligible for more positions (Air Combat Mages require a minimum rank of A, for example). Also, while the Combat Mage Rank of front-line soldiers like Nanoha and Fate is a decent gauge on battle prowess, there's also the less battle-oriented Composite Mage Rank and... well, to use the SS-Ranked Lt. Col. Hayate for example, she mentions that any of the Forwards under Nanoha's tutelage would kick her butt in a duel. Including Caro. Without her dragons.
In Claymore, there are normally 47 of the titular warriors, and they're ranked from 1 to 47, based on their relative power. Thus, it's possible for someone to go up in the rank, not because they got stronger, but because someone of higher rank died.
All jutsu and missions in Naruto are ranked. Usually this scale goes D, C, B, A, S. Jutsu rankings indicate ease of learning and personal risk to the user, and a few Jutsu like rope escape and transformation are E-ranked. In the case of missions, however, it's a bit more realistic, as there is an organization giving out the rankings for a plausible purpose (assignment of missions to appropriately ranked ninja and charging of appropriate fees), and the rankings are shown to be mistaken on occasion (Tazuna lies about how dangerous protecting him is because the Land of Waves can't afford an A-rank mission).
The ranking of village-affiliated ninja themselves, however, is limited to a four tier system of chain-of-command: Genin ("low ninja"), Chuunin ("middle ninja"), Jounin ("high ninja"), and Tokubetsu Jounin ("specialist high ninja"; despite how it sounds is actually lower ranked than a regular Jonin). This is sensible — a village promotes a ninja who has proven he has gained the combat experience necessary to lead other ninja; this naturally goes hand-in-hand with becoming stronger, but a ninja can (and has) become the superior officer of more powerful ninja who were not ready to take command. However, if a ninja never takes the promotion tests, they will go unpromoted despite being appropriately qualified — as Naruto himself proves, being absent when all of his friends retook and passed the Chunnin Exam, and thus remains a genin.
There's also the Kage rank, which theoretically is supposed to go to the absolute no questions strongest ninja in the village. In practice, however, Konoha at least is decided by a majority vote of the village's Jonin and then waiting for approval from the Daimyo of the Land of Fire. If you're severely lacking in the ability to mix it up with people who can legitimately claim to be Kage tier, but are incredibly famous, then you can get the position no questions asked.
During the Chuunin Exam arc, Kabuto has data cards (based on his own research, or so he claims) that numerically rank the various examinees on traits like physical strength, agility, and skill in various ninja arts. The accuracy and usefulness of these ratings never gets closely examined.
A similar set of six traits (Strength, Speed, Stamina, Ninjutsu, Taijutsu, and Genjutsu) are given for most characters in databooks specific to a period of time, each being a multiple of 1/2 from 0 to 5. It isn't clarified whether this numbers are supposed to some sort of quantitative measure or percentiles. While the first three have obvious ways in which they can be measured, there are a number of different factors the other three could potentially be referring to (variety, raw power, efficiency, difficulty of the techniques they have learned), especially with ninjutsu which is what essentially ever technique that isn't based on bare-handed-attacks or illusions. For instance Hidan is given a Ninjutsu ranking of 5, but only showed use of one technique that is classified as ninjutsu.
Ninja are also S-D ranked in each village's "bingo book", presumably based on how difficult a mission it would be to take them out. This is largely only referenced with respect to "S-Rank" missing ninja, such as the members of Akatsuki.
YuYu Hakusho uses this starting from the middle of the Dark Tournament arc on; Toguro is a high-level B-class, while the heroes are low to mid level Bs, IIRC. Later on they're all high As, but a veritable swarm of S class show up, the first of which is Sensui, the World's Strongest Man, ranking at a low S-class...
The S-class is stated as being "everything so strong that hell cannot do anything against them"
Fate/stay night. Servants themselves aren't given a single arbitrary Rank, but their individual parameters are. The arbitrary part is because each parameter is the sum result of various unmeasured factors — ATK (attack) Rank is influenced by arm strength and weapon power.
And individual Noble Phantasms also receive their own ranking based, roughly, on how much destruction they are capable of causing with a single use; anti-personnel, anti-army, anti-castle, or anti-world. That last one has annoyed people for a long time (can it destroy the world? can it destroy all the people in the world? Is it just called that because it breaks the 'rules' of the world's reality? Who knows, the series never tells us!).
Dragon Ball Z: the existence of in-world "scouters," devices that estimated how much power a potential combatant had relative to an unspecified standard, allowed fans of Dragon Ball Z to know the exact odds for any encounter. While eventually the characters became so powerful that their numbers "could not be estimated," that didn't stop fans (or series guides, or games) from assigning them numbers through research and guesswork.
Word of God says that the scouters and power levels were phased out precisely for the reason that assigning mathematical odds to fights started feeling silly.
The entire reason for introducing the scouters and subsequently power levels was to show how silly it was. The villains constantly get the shaft because of their over reliance on battle power to determine who'd win.
One Piece uses a bounty system as a rough power ranking: The navy issues a bounty on a pirate relative to the threat the navy believes he represents. Inaccurate as it may be, it works because the characters believe in it; enough that pirates with high bounties can make lesser pirates pee their pants with their mere presence, and you get lines like "How could pirate X beat pirate Y? X Has a mere 50 million bounty while Y has 150 million! It can't be!" Of course, it's a direct tribute to Dragonball's power ratings.
Your bounty is directly related to how much the World Government wants you off the seas. This doesn't necessarily have to relate to strength but it generally does, with notable exceptions like Nico Robin, who received a 79 million Berry bounty at the age of 8 for being able to read Poneglyphs, rather than being a strong fighter. This fact is directly exploited by Blackbeard, who, despite being one of the strongest men in the world, had a bounty of 0, being Genre Savvy enough to stay off the radar until he was ready to make his move.
In reference to the 'threat level = bounty' idea, among groups with relatively similar power levels the highest bounties tend to go to the most Ax-Crazy. Examples include Donquixote Doflamingo of the Seven Warlords of the Sea and Eustass Kid of the Supernovas. This makes sense since, all other things being equal, someone who goes around slaughtering people For the Evulz would be considered more of a threat than someone who raids the occaisional merchant ship.
It's been stated that the most wanted man in the world is the Revolutionary Dragon. This probably has little to Power Levels and more to do with the fact that he's the head of an organization that wants to violently overthrow the World Government. Basically he's the most wanted by the World Government in the same way that Osama Bin Ladin was the most wanted by the U.S. Government.
During the Enies Lobby arc, one character had a (apparently annoying) habit of ranking the other members of his assassin group based on how hard they hit, measured in Dourikis. The average marine has 10, most of the CP9 members have 600-800, Kaku and Jyabura have 2,200 and 2,180, respectively (and Jyabura is upset over the very small difference), and Rob Lucci has 4000. Interestingly, the actual leader had a score of nine, a subversion of the usual Authority Equals Asskicking.
Seen in A Certain Magical Index, where espers are graded depending on the strength of their power, from 0 to 5. It's possible for one to ascend from a lower rank to a higher one, but extremely difficult. The main character, Touma, has a power that's officially ranked level 0 because his power isn't actually an esper ability, negating any ability he might have had otherwise. Imagine Breaker is still at least on par with any level 5 power out there: his right hand destroys any esper power and magic spell that it touches, meaning he can block anything from stray magical flames to raw kinetic force that would turn anyone else into a fine mist. This pisses off one level 5, Mikoto, who doesn't understand how he's never been stopped by her lightning bolts despite the sharp disparity in their rated powers.
A more random version is the numbers within the Level 5's. They aren't combat strength, although, with a few exceptions, it works as such. They seem to be an indication of how important they are to research.
It should be noted that even though 3-7 among the level 5's appear to be random with Misaka(3) and Mugino(4) about even and Gunha(7) apparently more impressive than Misaka, Accelerator(1) and Kakine(2) are by far stronger than the other level 5's. Even than Accelerator is capable of curbstomping Kakine who to be fair was actually able to hurt Accelerator. The rest of the level 5's aren't even capable of touching Accelerator much less hurt him.
Kiddy Grade has C-class, S-class, and G-class ES members, where their class refers...well, approximately to the awesomeness and/or power of their ability.
Deliberately invoked in Kenichi: The Mightiest Disciple, when the Nijiima, the local gossip and all-around rodent of a man ranks Kenichi's "Fighting Rating" at 62, and and Takeda, his next opponent at 80, to which Kenichi points out that the numbers mean absolutely nothing, and actual fighting can't be ranked like that.
In the Manga version of Sailor Moon S, the Witches 5 have levels assigned to them. Eudial is level 78, Mimete is level 40, Tellu is level 404, and Viluy and Cyprine are level 999.
Negima, in the manga version, does this with Jack Rakan's power chart. Of course, he states that other factors determine the chances of victory, but his basis for the data is questionable at best. One character even mentions who'd ever fight an Aegis Warship, and Negi, who's power level was 500 at the time imagined himself losing to 1001 cats, each with .5 worth of power. On the side of that were letter rankings, with Negi just slightly above A, while the 'Mysterious Boy' had a power level of around 3000 and a ranking of AAA.
In Fairy Tail, we actually rarely hear about rankings other than the S ranked members. However, it's somewhat subverted in that while the likes of Gray and Natsu are presumably A rank, they've both taken down S ranked mages without much difficulty and Erza admits to Jellal that an enraged Natsu is probably on par with her and Makarov agrees during the Laxus arc. They're wrong, of course, but Erza is just incomparably badass.
Bleach: The Espada are officially raned from one to ten. They're actually ranked from zero to nine. The fandom thought they were ranked on strength even though the manga never claimed that. On that basis, numbers five to ten made sense but numbers one to four seemed completely random, with #2 and #4 looking much more powerful than #1 and #3. When Word of God clarified that they're ranked on reiatsu level, not physical strength, the ranks made more sense; skill and special ability are left out of the equation, #4 was ranked on his publicly known reiatsu (not his secret level), and the #1 Espada was Brilliant, but Lazy, meaning he never fought properly anyway. It also explains how Yammy can outrank Starrk, because he was a raw powerhouse who was lampshaded many times in-story as being completely incapable of actually harnessing his power in any useful way.
X-Men's aren't really Power Levels, unless you think Mr. Immortal, an Omega Rank mutant, is one of the strongest mutants out there (Mr. Immortal's power is to return from the dead... and that's it.) Hell, every X-Men character has that power!
In the movie series, mutants are apparently graded on a five-tier system based on the potential abilities their mutations give them. Magneto is a Class 4 mutant, while Jean Grey is a Class 5.
Averted by the Mutant Threat Rating used by the government in The 198 Files, which takes into account personality as well as powers. Kitty Pryde is ranked on the highest level (up there with Magneto!) simply because the agency making the files knows she's strongly moral and can't be bought, controlled or silenced, which coupled her intangibility power makes her a massive potential security risk to their black ops.
There's also the 100 Ton system for strength, which measures how much a character can bench-press and doesn't actually go beyond 100 tons, choosing instead to merely Hand Wave it as "at least 100 tons", so you'll find people like Hulk in the same tier with like Luke Cage or some shit (and even then it's not solid, given how Strong as They Need to Be comes into play).
Marvel's official site has a seven point system for abilities - although the resulting insensitivity of the scale has led to some gross errors in ranking, especially when comic book power levels technically range from Street to Cosmic.
It gets worse if you take into account the power rankings on the trading cards, which often seemed to be assigned completely at random. Fortunately those aren't canon.
A guide breaks it down to six categories based on appearance and/or level of power and control.
In Ghostbusters, Peter Venkman invents a bunch of technobabble to describe a ghost that includes referring to it as a "Class V." The Ghostbusters roleplaying game makes this legitimate, creating an entire system of classes with Roman numerals.
The ranking system here doesn't necessarily rate how difficult a ghost is at handling. Rather, it's just a simple system for categorizing ghosts. For example, the only difference between Class III AND Class IV is if the ghost can remember its name, Class VI are non-human, and Class VII are metaspecters (that is, demons, deities, and the like). Classes III through VI aren't necessarily progressively more powerful, smart, or difficult to handle, just less and less human.
Discworld wizards rate magical ability from Level 0 - Normal person to Level 8 - Supreme wizard. This terminology is dismissed as basically meaningless by Granny Weatherwax ("It's all part of the game") and even wizards acknowledge that it fails to define sourcerers (Level Infinity) and Rincewind (Level some negative number).
Although, after he defeated a sorcerer he's technically one himself now. He's also a professor, but that's totally within the trope of random titling even in the real world.
The level system is even more useless when you consider that in the pre Archchancellor Ridcully days, you generally attained such positions by killing all the wizards between you and the position you were after.
Its uselessness was precisely the point. Even after the Sourcerers, Wizards were still relatively powerful and ambitious. Since every rank has a maximum capacity applied (eg. only eight Level 8 wizards at any given time), it encourages a Darwinist approach to rank ascension. In the end, Wizards ended up fighting each other for meaningless titles instead of, say, enslaving the Muggles and so on.
The gameline of Hero Clix has a point value (or Power Level) for every Comic Book character they've turned into a figure. These values are added for all the heroes and/or villains on your team (to make 100, 200, 300 or more point teams); however these are secondary to the traits and powers the "clix" or figures have. Things like Spider-man's ingenuity are treated as Outwit, an power canceling power. Probability controlling heroes get Probability Control, letting you reroll bad dice. Players themselves can value a "weak" 20-30 point figure over a 100 point one because it's more efficient or has powers in a better order. All in all, it's a fairly robust system.
Like most miniature games, Warhammer 40,000 assigns each figure a points value to reflect its effectiveness (an Ork is 6 points, a Space Marine 15 points, and so on). The setting itself also features this to a degree, as the Imperium assigns "threat ratings" to different aliens (a Tyranid Gaunt is "minimal," while a Carnifex is "extreme").
40k background also features a system to classify the power level of psykers (people with psychic powers), known as "the Assignment". The ranks are based on greek letters. The exact details are not known but, to sum it up, Rho and Pi encompass average non-psykers (e.g. common human being); Omicron to Kappa denote unconscious and uncontrollable psyker talent that is of such a minor level that it only manifests under high stress, and gets frequently handwaved by the common citizen as "good luck" or "fluke"; Iota and above are the "true" psykers, including the battlefield-worthy "Sanctioned Psykers"; Delta and Gamma are 1-in-a-billion kind of rare, and deemed a true security threat that must be "acquired" by Imperial authorities; and Beta and Alpha possess too high psychic power for the human mind/brain to handle, and thus the majority of them tend to be mentally unstable at best. And beyond those is Alpha Plus, which is reserved for the guys who can mind-control cities and snap a Humongous Mecha in half with their mind; the only known verified example is the Emperor of Mankind. At the other end of the scale (i.e. Sigma to Omega), "negative" psyker ranks denote people with negative warp presence (who do exist and are extremely valued for their ability to cancel enemy psykers and ward against demonic influence). Sigma and Tau are merely "psionically dense" (i.e. the Tau racenote Yes, parts of the fandom have inevitably had a field day with this "coincidence.), while Upsilon to Psi have varying degrees of anti-psychic resistance, and Omega designates the rightly-dreaded Untouchables (a.k.a. Blanks, Pariahs), who are basically walking fields of psychic Anti-Magic that are described as being effectively soulless.
Also in-universe, the Inquisition uses a two-part rating scale to classify threats to humanity. The first part describes the nature of the threat: Hereticus (human, mutant, or abhuman), Xenos (alien), Malleus (daemonic), and Obscuro (true nature unknown). The second part gives the danger of the threat, and ranges from Minima (poses little threat to a competent fighter) to Terminus (potentially world-ending or worse).
This can happen when players in point buy systems that give non-combat abilities like wealth or beauty a point value use those same values to determine how powerful a character is.
In almost much every RPG with point-based character creation, there are ways to make a more effective character with fewer points by making use of more efficient builds. So the point-totals of characters doesn't always work as an overall measuring stick of power. As an extreme (and deliberate) example, in Tri Stat it's possible to use 140+ points (theoretically a superhero-level budget) to build a character who is inferior to a 24-point completely-unskilled average human.
The first edition of Dungeons & Dragons classified every monster with a Roman numeral from I (giant rats, goblins) to X (ancient dragons, demon princes). These classifications were combined with monster rarity to put together encounter tables ... though frankly, virtually every level X monster was incredibly rare in any game world with an ecosystem.
Due to a combination of this and Gameplay and Story Segregation some of the cards in Magic: the Gathering for the legendary creatures from the varies novels tend to be all over the place. The standard example is that Gerrard Capashin, the hero of several of the novels, has a card that would lose in a straight up fight to most if not all of the foes he defeated over the course of the storyline. Moreover, due to balance reasons and the fact that 1/1 is the smallest a creature can get you can end up with bizarre situations like a dragonfly successfully killing an elite soldier.
Character Point scores in GURPS are sort of a power ranking but since they measure absolutely everything about the character using them as rankings turns out completely random. The classic example is the 1000CP accountant who can mentally collate spreadsheets with all the money going through multinational corporation but will lose a fight to a 50CP thug.
In the Mega Man X series, X is ranked B, while Zero is S (or SA). In the later games of the series, completing levels with zero deaths, finding all the hidden items, taking minimal damage, etc, allowed you to get a higher hunter ranking, which went as high as MH/UH. (D, C, B, A, SA, GA, PA, MH/UH for X5/X6; D, C, B, A, AA, AAA, S for X8)
At least there's an actual in-universe reason for X and Zero's initial rankings. Zero is capable of getting the job done no matter what the cost or danger, and therefore gets the highest rank (at the time), Special A class. X, on the other hand, dislikes fighting, and is hesitant in combat situations that require decisiveness, resulting in a lower ranking even though he's just as powerful as Zero.
Gets stupid considering that, at the beginning of X5, X is still considered a B-rank hunter despite bringing down Sigma on at least four separate occasions. Somewhere over the course of this game he canonically jumps all the way to Special A class. Exactly what made the difference is never made clear - perhaps Signas just thought he looked cool with Zero's Laser Blade?
At the conclusion of X5, X has lost the hesitation that held him back, becoming as confident as Zero (hence Special A). X7 made him go in the complete opposite direction. He gets better in X8 and Command Mission.
To wit, by the time of X8 and Command Mission, X, Zero, and Axl are all canonically considered to be legendary S Rank Hunters.
Mega Man Legends uses these for Digger licenses (higher license means you can access better dungeons). The S-Class license doesn't actually give you any special access, which is good, since the test to get it is a pain in the butt.
Guilty Gear uses a letter grade for the threat levels of characters, with Dizzy being ranked S due to her being a Command Gear that could cause a war. Unusually, the organization assigning the rankings seems to place extra emphasis, not simply on combat ability, but on political clout and how easily a given character is to manipulate, neither of which has any real practical relevance in a fighting game. Several highly-trained professional assassins and ninjas are given fairly low ranks due to the fact that their various quests for vengeance make their movements easy to predict and control, and when you get right down to it, "killing people" is pretty much their only skill set.
In Sonic Adventure 2, there are A B C D E ranks that indicate how well you completed a level and how good your Chao's stats are.
Chao stats can go as high as S, which is one rank above A.
Many Sonic games (most of the main series since SA2) use this letter ranking system, and many that don't use some other type of letter ranking. For example, Sonic Rush had S A B C ranks, based on how quickly you completed the level, how many tricks you did, and how many rings you had. There was a cap for the maximum number of points each could give.
In the Fire Emblem games, a character's ability to use a type of weapon (sword, lance, axe, bow) was ranked by S, A, B, C, D, and E, with S as the highest and E as the lowest.
Many rhythm games score you on a letter scale after a stage. Dance Dance Revolution, granddaddy of them all, goes from F to AAA (and AAAA on unofficial simulators), while In The Groove uses all the normal letter/± combinations plus S-, S, S+ , and one to four stars.
Also some mods of Unofficial simulators go up to AAAAA
The Resident Evil series does this a lot, as well, with rankings from F to S depending on how well you did in the game (overall time, health items used, etc). Resident Evil 5 took this to an extreme by ranking you for each individual chapter, as well as the game overall.
Subverted for the weapons in Team Fortress 2, which are graded by levels: stock weapons being level 1 while unlockables being higher. The levels make no difference whatsoever, because the game is designed to be as balanced as possible, and are there for purely cosmetic purposes.
The levels were actually supposed to be the number of achievements for that class you needed in order to unlock the item. There was a bug that caused the levels of the random drop items to be randomized, so players hoarded the high-level items for bragging rights.
Garou: Mark of the Wolves gives you a rating after each round you win. They go C, B, A, AA, S, SS, SSS, and MIRACLE. You have to destroy your opponent in roughly five seconds to even have a shot at the higher two rankings.
Viewtiful Joe has five rankings for quality - V(iewtiful), A, B, C and D. It's possible to get a "Rainbow V", if the player gets all Viewtifuls for a level, and getting Rainbow Vs on every stage unlocks unlimited VFX.
Picross DS awards rankings A through E for Daily Picross based on time, and grants an S ranking overall to players who have As on all the types of Daily Picross.
In Wild ARMs 4, Yulie and her fellow test subjects are raked by a lettering system based on their abilities to control the titular Arms. A B+ like Yulie can control but not wield arms and a F like her brother needs a drug to even gain control of an Arm
In Elite Beat Agents, your score (due to the bonuses it gives) is based primarily on how many hits you get in a row. Your rank is based off how many 300s, 100s, 50, and Xs you get. They are independent of one another, so you can get a higher rank but with a lower score.
Mass Effect averts this: letters denote military operational specialty, and numbers denote proficiency and commendations in that MOS. The numbers go from 1 to 7. The only letter that has been explained is N, which is special operations (it's assumed that whatever Joker's letter is, his number is definitely 7).
Urban Rivals assigns cards a minimum and maximum star rating based on it's current abilities and stats, to limit the total power of a hand in tournament matches and better equalize for skill of play. Often the ranks are based on cards with similar function, sometimes they're evaluated based on play-testing before release. A few have been re-ranked due to unexpected gameplay impact, but cards that turn out to be so off-the-scale that they're broken are simply banned from tournament play.
Ghostbusters: The Video Game showed the different classes of ghosts whenever you scanned them. Class I was pathetic, not even needing to be captured, just dispersed with the proton pack. Class III's and up require capture, but III's aren't a big deal. Class V's are somewhat nasty. Class VIII's are huge and dangerous, capable of incapacitating a Ghostbuster with one hit, and are usually deities or otherwise superpowered. There's only one Class IX in the game, and it's the final boss.
In the Darkstalkers series, monsters are ranked by letters. "S" Class is powerful enough to be considered a god, "A" Class are the rulers of Makai, "B+" Class is what most of the playable characters are, "B" Class is an average creature that can wipe out a first-class human army, "C" Class is probably what you are, and "D" Class is but a wild beast.
In the StarCraftExpanded Universe novels, terran psychics are given a Psi Index (PI) rating, from 0 to 10. A typical terran has a rating of 0-2, those with a rating less than 5 have weak powers such as the ability to sense psionics or feel others' emotions, and those with a PI of 5 or above can read minds and are required to become ghosts. PI 8 or higher allows (but does not guarantee) telekinesis, and is extremely rare. Only three psychics have rated a PI 10 without drug enhancement. Two of them, Nova Terra and Sarah Kerrigan, are major characters. Their powers, especially Kerrigan's, went through a lot of Power Creep, Power Seep in the novels. Zerg can have psychic powers, and protoss always do, but they're not rated on the same scale.
The Monster Hunters in Monster Hunting Made Easy had rankings from A to Z with A as the highest. The comic often made fun of S ranks. One character with an S rank thought that it was the highest, just like in many video games. He was then told that the S stands for "special".
In Captain SNES: The Game Masta, there is a database that holds the power data for every character. The characters actually are given four ratings, which correspond to their characteristics. The guide for this can be found here◊ and the database itself can be found here.
In Patchwork Champions, there are both H and V rankings on a scale of 1 to 10. An H ranking is for heroes, and is based on the usefulness of their powers to rescue and protect people, while a V ranking is for villains, and based directly on how your powers benefit you personally. Essentially, someone with a high V fighting someone with a high H should have the V win, but once you start introducing other people the system stops working for power.
One episode of Extreme Ghostbusters features the Tentabrog, considered a class 13, a class never seen before. However, all it took to defeat the ghost was to smash the orb it was bound to.
The belt color systems used by many martial arts can be seen this way.
The US military has something similar to this. Some jobs require the ability to lift various amounts of weight, and they assign these to letters. For example, being able to lift 60 lbs is J and allows you to be in J strength jobs, while being able to lift 100lbs is rated N. The full list is E: no requirement F: 40-lbs G:40+ lbs H:50+ J:60+ K:70+ L:80+ M:90+ N:100+ and P:110+
The IDF assigns two primary values to each new recruit: a medical rating called a "Profile", and a catch-all behavioral rating called a "Quality Group" value. These determine the recruit's potential, which corps he/she will serve in, which jobs will be available to him/her, etcetera. These values are meticulously calculated from all the information the military has on the recruit (including interviews and examinations done before recruitment), but the result is often a completely arbitrary classification of a person based on very incomplete data. Then again, with dozens of thousands of recruits to process each year, there really are no alternatives.