I use the UBI site's calculator, it's always be spot on for me:
http://www.bikeschool.com/spokes/index.cgi

It requires flange diameter and center to flange in addition to the regular info.

I get ~300mm for the rear wheel if the hub flange is 40mm and center to flange is 25mm. I get 301 in the front with 25mm flange diameter and 25mm center to flange. If you make more accurate measurements you may get better results.