This article is from the Triathlon FAQ, by with numerous contributions by James Goddard others.
There are no set distances for triathlons. Many triathlons use various
distances that conform to the land/water available to them.
There are, however, a few "common" distances:
Name Swim Bike Run Sprint .75km 20km 5km Olympic or International 1.5km 40km 10km Long Course 2.4m 112m 26.2m