There are a lot of charts and calculators out there. Most go off a rider`s height which is bogus. Tell your freinds the reason why you go by weight is because the board could care less about height, but weight directly effects how it will perform. Weight affects flex, camber, torsional flex rebound etc. The only time height is a factor is if a person is really out of the normal range like your 5`7"" 110 pound beanpole there. He might need a bit longer board than is ideal for his weight, simply because a board that short would not allow him to place his bindings far enough apart. Riding conditions and skill also plays a huge part. Always use weight as your reference point, then adjust for unusual height/weight ratios or task specific reasons such as choosing a very long board for strictly pow or a short one to learn spins and jibbing.
I tried on my nephew`s 149 and I am a 6 foot, 180 pound guy....that board was super unresponsive, but I sure could spin the thing easily...
Of all the calculators out there, I found this to be about the most "in the ball park" it also has a board suggestion that is kind of helpfull. It is kind of fun to throw around some numbers and see what you get. It was real acurate for me.
Snowboard Sizing Guide, Size Calculator