The number system used by most of the modern world today is called the decimal system, involving ten digits ("Base 10"). Sometimes, if a writer wants to portray a society as being significantly alien to our own, they will include a mention of an alternative number system for this society, with the "base" being a number other than ten.

This may be used to indicate the collective intelligence of the society that produced it, if it is portrayed as more sophisticated or more primitive than our system. There may also be an inferred correlation between the ten digits in our number system and the ten digits on the average pair of human hands. Therefore, a race of aliens with FourFingeredHands may use a base eight number system. Finally, it is very common for robots or other computer-based intelligences to count in base two.

This sort of thing is generally used as an insignificant [[GeniusBonus throwaway joke]], with "ordinary" numbers [[TranslationConvention applying before and after]], as it may be a [[ViewersAreGeniuses difficult concept]] for some viewers to grasp.

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!!Examples:

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[[folder:Comicbooks]]
* In ''ComicBook/ElfQuest'', the elves use base 8 because of their FourFingeredHands -- that page has more details.
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[[folder:Fan Works]]
* ''Fanfic/AeonNatumEngel'': The narration from the [[TabletopGame/CthulhuTech Migou]] POV and their dialogue goes to great lengths to convey their alien thought processes, including a base-36 numbering system.
* In ''Webcomic/{{Hoofstuck}}'', Twilight Sparkle mentions that Equestria uses base eight rather than ten, since there's nothing on a pony you can use to count to ten (whereas four hooves times two make more sense). They used to run with base four originally, symbolising the four races (earth ponies, pegasi, unicorns, alicorns) but the earth ponies took offense at being considered the "zeroes".
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[[folder:Film]]
* [[AllThereInTheManual Behind-the-scenes material]] on ''Film/{{Avatar}}'' claims that the Na'vi also use base 8 for the same reason as the ''ElfQuest'' elves.
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[[folder:Literature]]
* In the ''Franchise/StarWarsExpandedUniverse'', the Hutts use a base 8 system due to only having four fingers on each hand. Being Hutts, they don't always tell this to their business partners, most of whom use base 10.
* In the ''Literature/{{Discworld}}'' books, trolls apparently have a "base Many" system (actually base four). As in, "one, two, three, many, many-one, many-two..." This is revealed in ''Discworld/MenAtArms'', when it turns out that Detritus is not incompetent with numbers, he is in fact very good at counting ''in powers of two''.
* A subversion in ''Literature/TheRestaurantAtTheEndOfTheUniverse'': When Creator/DouglasAdams revealed that the question which produced the Ultimate Answer (42) was [[spoiler:What do you get if you multiply six by nine?]], somebody pointed out that the math actually did add up, using base 13. Adams responded, "[[SelfDeprecation I may be a sad individual]], but [[EvenNerdsHaveStandards I don't make jokes in base 13.]]"
* According to the appendices of ''Literature/TheLordOfTheRings'', elves habitually count in base 12.
* The ''gukuy'' in EricFlint's ''Literature/MotherOfDemons'' count using an eight-base system.
* It's never mentioned in the books themselves, or the series, but the "Gallifreyan numerals" used on the spines and chapter headings of the ''Series/DoctorWho'' New Series Adventures (9th and 10th Doctors) are in base 7.
* In Leo Frankowski's ''The Cross Time Engineer'' series, the new civilization Conrad Stargard starts up in Medieval Europe uses base 12 mathematics, because Stargard believes it's "more accurate" than decimal mathematics.
** Not so much more "accurate" as more useful. Bulk goods are bought and sold in dozens and grosses. 12 factors into 2, 3, 4, and 6. It is far easier to cut a cake/pie into 12 pieces than ten without involving a protractor.
* In ''Learning the World'' by Creator/KenMacLeod, the aliens are four-fingered, and count in base 8. When they learn that humans use base 10, their reaction is that having a base that isn't a power of two must be awfully inconvenient.
* In ''Literature/AFireUponTheDeep'' by Creator/VernorVinge, the doglike Tines have two different number systems: one where they count "by legs" (in base 4) and one where they count "by fore-claws" (in base 10). Confusion between these two systems leads to the accidental meeting of two of the major characters. Amdiranifani is housed in room 33, Jefri is supposed to be imprisoned in room 15 (33 in base 4), and the guard who's taking him there uses the wrong numbering system.
* On Literature/{{Gor}}, the alien species the Kurii use base-12, presumably because they have 12 digits on their "hands."
* ''Literature/LittleFuzzy'', a series begun by HBeamPiper, uses a modified form of base 5. 1, 2, 3, 4, one hand. At 125, they've reached a hand of hands. It then goes to many, and many many. The fuzzies soon adopt the humans' base 10 system.
* Creator/LarryNiven and Jerry Pournelle's ''Literature/TheMoteInGodsEye''. The Moties have a total of 12 digits on their right hands and use base 12.
* The Kzinti of Creator/LarryNiven's ''Literature/KnownSpace'' count in base eight.
* Literature/TheCulture uses a nonary (base nine, that is) system for their writing, although it's actually binary in a 3x3 square. Binary is mentioned as being used by some civilisations, and powers of two are the closest thing to a universally-regarded 'round number'.
* In ''Literature/StrangerInAStrangeLand'', the Martians apparently have a numerical system based on three and powers of three. "Three fulfilled," they call it...
* [[AllThereInTheManual According to]] ''[[Franchise/StarTrek The Klingon Dictionary]]'', the Klingons used to count in a ternary (base-three) system, but have since switched over to decimal.
* In ''Literature/{{Footfall}}'', the Fithp use base 8.
* In ''Literature/{{Contact}}'', a message is encoded in base 11, by someone or something capable of messing with the values of mathematical constants.
* The aliens in the ''[[RendezvousWithRama Rama]]'' books appear to use base 3.
* In ''The Iron Standard'' by Creator/HenryKuttner, the six-fingered Venusians use base-12.
* ''Literature/OutOfTheDark'' gives us the Shongairi, who count in base-twelve. Possibly.
* Zamonien in Creator/WalterMoers' novels uses base 8. The author even created new symbols for the numbers.
* In the ''FightingFantasy'' book ''Rebel Planet'', the two-fingered Arcadians count in binary. Converting binary to decimal is necessary to solve a couple of puzzles, though the reader is fortunately provided with a handy grid.
* Centaurians in ''Literature/ThePentagonWar'' have 4 tentacle-fingers on each of 4 hands. When a Centaurian named Torra Zorra reads that a cable's diameter is 3 x 10[[superscript:-5]] meters, we get this parenthetical aside:
-->(Curse the human penchant for powers of ten! Torra always had to mentally convert their numbers to base sixteen, just to get a handle on them.)
* The Megarites of the ''Franchise/StarTrek'' universe use base 8, according to ''StarTrekExMachina''.
* In ''Literature/BattlefieldEarth'' the Psychlos use a base-11 system (they have an extra finger on one hand). While this causes the human characters endless frustration when trying to work with Psychlo mathematics, it gets nonsensical when other alien races share these complaints, lauding the values of a sensible base-10 system and concluding that the Psychlos were just being perverse when designing their math.
** It doesn't help that Psychlo mathematics requires that the user have a basic knowledge of the Psychlo homeworld's geography. Yet another bit of evidence that they're just trolling the universe.
* Gully dwarves from ''Literature/{{Dragonlance}}'', being astonishingly stupid, can only count up to two. Any higher quantity is described as "One and one and no more than two."
* In ''Literature/ChildhoodsEnd'' by Creator/ArthurCClarke, the Overlords are mentioned to count in base 14 (their hands have five fingers and two thumbs).
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[[folder:Live-Action TV]]
* ''Series/StargateSG1'':
** A throwaway comment in the episode "The Fifth Race" implies that the [[{{Precursors}} Ancients]] counted in base eight.
** Also invoked when they nearly set off a Tobin mine by entering in the wrong code due to Daniel failing to factor in a zero into his translation. He argues the Phoenicians they were descended from never used a number zero, but Carter points out in order to program something as complex as a mine, the Tobin's would have ''had'' to have added a zero component.
---> '''Carter''': Trust me; its a math thing.
** There's a fan theory that the constellations on the gate actually correspond to digits in a base-38 number system. Which means that a gate address is not six arbitrary points in space with the destination at the intersection,[[note]]which contradicts the in-series assertion that all addresses are unique[[/note]] but three two-digit base-38 coordinates.
* In TheFrantics' sketch [[http://www.youtube.com/watch?v=fjFaKD9BuOc "Roman Numerals"]] a Roman citizen is baffled by the new decimal system.
-->Customer: How much is "forty-four" in real numbers?\\
Shopkeeper: XLIV [[note]]pronounced "ex-ell-eye-vee"[[/note]].\\
Customer: Well why don't you just '''say''' XLIV? Who can remember "forty-four?"
* In ''Series/StarTrekTheNextGeneration'', the [[MeaningfulName Bynars]] use base 2 (i.e. binary).
* ''Series/BabylonFive'':
** The Mimbari use base eleven (a byproduct of using fingers, toes, and the head as "digits" for counting).
** According to tie-in RPG materials, the Dilgar used base 25.
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[[folder:Tabletop Games]]
* In ''{{Traveller}}'', the various alien species use different base mathematics. The Aslan use Base 8, the Hivers use Base 16, and the Droyne use Base 6. Most of the various {{Human Alien}}s, as well as the Vargr, use Base 10.
* The ''TabletopGame/{{Warhammer 40000}}'', the Tau use base 8 owing to their FourFingeredHands, leading to a delicious little StealthPun: their [[MiniMecha battlesuits]]' designations are based on their size, such as [=XV25=] for the smaller Stealth suits, [=XV8=] for the main Crisis suit, or [=XV88=] for the heavy Broadside variant. Which means that the new [=XV9=] Hazard Close Support Armour units are taking things UpToEleven.
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[[folder:Video Games]]
* In the ''{{Myst}}'' games, the D'ni have a base 25 system, in keeping with the games' general tendency to use powers of five as {{Arc Number}}s.
* The aliens in ''VideoGame/{{Iji}}'' use a ternary number system.
* During ''VideoGame/{{Portal}}'''s boss fight, after GLaDOS takes a missile hit she'll announce "Two plus two equals... ''ten!'' In base four I'm fine!"
* There is a popular theory among ''VideoGame/HalfLife'' fans that the Combine use a base-17 system, based on how [[ArcNumber prominent]] 17 seems to be. If nothing, it reinforces the [[SufficientlyAdvancedAlien utterly alien]] nature of the Combine.
* The Kilrathi from ''Videogame/WingCommander'' use Base 8 for their numbering system, given that they have a total of eight fingers. For the most part this isn't really mentioned much, but it's prominent in the dates for history of the Kilrathi war from their viewpoint as done in the manual for ''Armada'', "Voices of War".
* ''{{Halo}}'' fans speculate that the Forerunners might have counted using a Base-7 counting system.
* A significant portion of the game ''{{VideoGame/Rama}}'', based on Arthur C. Clarke's [[RendezvousWithRama novel]] series of the [[TheGameOfTheBook same name]], involves solving mathematical puzzles based on the native number systems of the Avians (base 16) and Octospiders (base 8). (Which is at odds with the Ramans, who use base 3.)
** Of course, both the Avians and Octospiders aren't Ramans. They're just samples of other space-faring species that the Ramans had gathered.
* One puzzle in ''StarTrek25thAnniversary'' involves figuring out the alien code that is more difficult because the aliens in question used a base 3 system.
* One of the puzzles in the Kitchen in ''VisualNovel/NineHoursNinePersonsNineDoors'' requires you to use base 16 in order to figure out the code to open a locked safe.
* ''Franchise/MassEffect'' mentions math systems not based on ten, such as a superweapon that relies on specialized base-12 mathematics and a krogan NPC muttering about the stupidity of base-10 math and the consequences of having extra fingers.
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[[folder:Webcomics]]
* In ''WebComic/{{Housepets}}'', a mouse named Spo came from a very large family. How large? The sibling born immediately after him [[http://www.housepetscomic.com/2009/02/23/their-naming-conventions-had-a-cover-charge/ was named Spp]]...
* In ''WebComic/GirlGenius''' world of [[MadScientist mad science]] there's bound to be examples showing up: "Tell the landlord that he is to stop trying to make change in base eight, or he'll pay his taxes in base twelve."
* ''Cowbirds in Love'' [[http://cowbirdsinlove.com/43 points out]] that every base is base 10 (from the perspective of anyone using it). For bonus points, the alien in the comic uses base 4 and appears to be four-fingered.
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[[folder:Web Originals]]
* In some of the ChakonaSpace stories, Caitians are mentioned to be using base 8 math and the less mathematically minded ones struggle with everyone else's usage of base 10 math.
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[[folder:Western Animation]]
* In ''WesternAnimation/{{Futurama}}'', robots sometimes use base 2.
* The ''SchoolhouseRock'' music video for [[http://www.youtube.com/watch?v=4QpbO4MIAVE "Little Twelvetoes"]] briefly touches on the idea of what counting with a base-twelve system would be like, and demonstrates with the titular twelve-fingered alien character.
* In TheSimpsons Principal Skinner wishes he had enough funding for his school to buy, amongst other things, "math books that don't have that base 6 crap in them". This is almost certainly a reference to New Math, a way of teaching mathematics that was briefly popular in TheSixties but very rapidly fell out of favour.
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[[folder:Real Life]]
* Computers work in Base 2 because the only input signals they can distinguish between are "on" and "off". Each one is called a "bit". The de facto standard of a byte establishes it as 8 bits, prompting people familiar with computer science to use the hexadecimal system (base 16) to represent a byte of information in two digits.
** Bases that are powers of 2 are fairly popular in computer science, including the above-mentioned hexadecimal (base 16) system and octal (base 8) which is most commonly used with the UNIX chmod command for setting file permissions.
** There have been computers working in base 3 (called ternary or trinary computers) with three possible values: -1, 0, +1. The popularity of binary computers have turned them into a historical footnote, but their efficiency may yet bring them back, especially as we get into quantum computing.
* DNA is encoded (at the lowest level) in base 4. This is thought to provide an optimal compromise between error correction/detection and information density.
* "New math" had learning to do operations in bases other than 10 as part of its syllabus. It was also one of the things it was [[http://youtu.be/UIKGV2cTgqA mocked]] for.
* The Mayan languages use a base-20 system. Interestingly so do the Nahuatl-speaking ("Aztec") cultures, which no other members of that language-group do (Hopi, O'odham, and Shoshone are base-10), so it might be something the Aztecs borrowed from the Maya (or, just possibly, that both borrowed from the Olmec, who also probably had base-20).
* Ancient Babylonians counted in base 60. This is reflected in the modern measurement of time (hours, minutes and seconds), as well as angular measure (degrees, minutes, seconds). It came about because of two tribes. One used base 10, counting each finger, and a neighboring tribe used base 12, on one hand they would use the thumb to count the remaining twelve segments of the remaining four fingers. Since they had different systems, they would convert to a larger base. Sixty is the least common denominator between 10 and 12.
* Vestiges of base 20 remain in English ("four score years and ten ago") and in French ("quatre-vingts"[[note]]4*20=80[[/note]], also in the name of the Parisian hospital ''Quinze-Vingts''[[note]]15*20[[/note]] which was originally founded to house 300 patients). In addition, numbers after sixty and eighty go up to sixty-nineteen (''soixante-dix-neuf'', instead of seventy-nine) and eighty-nineteen (''quatre-vingts-dix-neuf'', instead of ninety-nine). It's thought to be either a Celtic or a Basque influence, or an influence of the "Vasconic language-group" (of which Basque is the only surviving member) ''on'' Celtic.
** Yan Tan Tethera is a system for counting sheep from the same Celtic origins, once widespread in England but now rare & found mainly in the North. It goes up to "jiggit" for 20, then the shepherd makes a mark, places a stone etc. and begins again.
* Many languages count in little endian up to a certain point and switch to big endian for larger numbers. For example, in English "16" is ''six''teen but "36" is thirty ''six''.
** Some languages are weirder: Arabic stays little-endian until ''100''. So "16" is ''sitta-`ashar'' (six-ten) and "36" is ''sitta-wa-thalaathuun'' (six-and-thirty), but "136" is ''mi'ah wa sitta wa thalaathuun'' (a-hundred-and-six-and-thirty). This, however, is a relatively modern construction. Like the language itself, the numbers were read from right to left; "sitta wa thalaathuun wa mi'ah" (six-and-thirty-and-hundred)
** In older English, it's also not uncommon to see constructions like "six and thirty", which is still how German, parts of Danish and old-fashioned Norwegian do it.
* [[http://www.dozenal.org/ The Dozenal Society of America]] is the premier American organization for the promotion of base 12.
* We use base 10 because our progenitors, those fish that first aventurated outside water, had five digits in each claw. Some others of that epoch that didn't have success had more or less fingers, and if they had been luckier colonizing the earth instead of the former we'd be using another base.
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