Of course, it's always best to check with the center where you will donate. My center likes them the 42" wide that we make (because we don't want to piece the backs). The minimum length of 50" and max of 60". My contact there, though, says that they'll take anything
The folks that accept the knitting/crocheting say no narrower than 36" and not less than 45" long.
Thanks, Terri.