fletcher is correct, BUT, most guys just measure their draw length by coming to full draw, and having someone mark the arrow where it contact's the bow's back ( the back is facing away from you at full draw, the belly of the bow is what your looking at when at full draw)and then add about an inch to this measurement for your arrows, so you have broadhead clearance.
If your bow is marked say for instance, 45#@26.5", but your pulling an arrow to 29"-
then your probably pulling more like 55#@your draw length (adding 3#s per inch more than what the bow is marked).
So.... your draw length would be 29" and you would be pulling 55#s and shooting an arrow cut to 30"bop (back of point).
hope this helps,
sammy