No it isn't easy, but if you are looking on-line, sometimes they say. If they don't, you can contact the site and ask the hole size.  If you are looking for a hole that will be tight, just be aware that even though the stated size might be 3.2 mm, it could be a liitle smaller.  Therefore, I always like to go a little bigger.  Also, if you are looking at beads with a 3.2 mm hole, you can't string a braided portion, you must thread unbraided strands and then start braiding again after the bead is strung. 
Karen