The tag has no wiki summary.

learn more… | top users | synonyms

9
votes
3answers
446 views

Why do the opposing sides of a D20 generally add up to 21

Most D20s I own (with the exception of poorly made foam ones or MTG spin-down dice) seem to have all opposing sides add up to 21 (20 + 1, 15 + 6, etc). Why is this? Who started this?