The average manga chapter for a weekly serialization is 17-19 pages, but the first three chapters have extra pages to set things up (IIRC, 45, then ~30, then 23). Monthly hovers around 30 or 40, bi-monthly sticks around 12-19.
A volume generally has about 192 pages in total, and is generally the only route open to OEL manga.
One-shots generally have the same amount of pages as the first chapter of a new series, so about 45.
edited 18th Mar '12 5:52:23 PM by burnpsy