This Ice Hockey Skates Sizing Chart should give fairly acurate sizing, keeping in mind that some models of the same brand can vary in sizes (and width) i.e. Mission Fuel 85 *size 9 E* is the same fit as Mission Fuel 100AG size *9 EE*
If the number is larger than 2.65, a normal width or D width, should be fine (much higher than 2.65, a width of C should be fine). If the number is between 2.5 and 2.65, try a wide or E width. If the number is under 2.5, an EE or extra-wide width may be best.