Pad size is preference to a degree. I can prefer to have a 32" pad, but if I did the landing gear would be below my knee and I'd be smacking my knees into the ice every time I went into butterfly.
I'm 6'3" and when I bought my 36" RBK 5K's, my knees were right in the middle of the landing gear. When I retired those pads two years later, my height didn't change at all but my knees were at the very top of the landing gear (and I'm 26, so I didn't go through a sudden growth spurt.

).
Shrinkage is a factor when buying pads; the foam compacts / settles and the pads usually lose an inch or two over a few years. New pads will shrink, so take that into consideration when doing a fitting. Similarly, when buying used pads, take into account that while that brand new 34" pad in the store fit you, a two-year-old 34" off eBay will measure more like a 33" or even 32", even if the pads are the exact same model.
I learned my lesson, I went up a size and wear 37+1" TPS Summits now. My knees were hitting the lower half of the landing gear, but after a year my knees are in the perfect position on the landing gear.
But for sizing, best bet is to measure your ATK and go from there. Since that measures your leg length, it's much more accurate than just going by your height.
http://www.goaliestore.com/board/equ...e-project.html gives a brief tutorial and is a great reference for matching your ATK to pad length of specific manufacturers and models.