Originally Posted by caspharm

Supposedly, the selvages are not included in the WOF (per a website I found), but if you measure most fabric, then the 44/45 includes the average (I've seen) 1/2 on each side- meaning you get about 40-42" usable fabric. Batiks can be narrower because they are done by hand and there is no selvage to speak off.

See http://www.fashiondex.com/howtos/htstfm4.php middle of the page. This an apparel fashion website, but the info in general should apply.