J.S.
post your question at a website called www.sewforum.com
there is an area specifically for sewing questions. I'm sure someone can easily answer your question there.
Also, it pretty much depends on what size pleat you want. (and from a mom who sews, don't put a whole lot of effort into this...relatively speaking, they are in a crib for such a short amount of time. My kids are now 5 and 7, having left the crib around 2-3 yrs old. I just made them gathered dust ruffles...and actually for their rooms I just made gathered curtain toppers and attached them with velcro to the crib).