The AMO measurement standard is the length from the nocking point at full draw to the pivot point (deepest part) of the grip, plus 1 3/4 inches. A 28-inch draw would be 26.25 inches to the pivot point, plus 1 3/4 inches. Your draw on that bow (.25 inches more but the riser is .25 inches shallower) is about the same so you should be drawing right about 38#, give or take a pound.
Another way to do it is to draw an arrow and have someone mark the arrow at the back of the bow at full draw and measure the length from the mark to the slot in the nock.
These measurements will usually be within a half inch of one another, which usually equates to a pound or so of draw weight.