If you weigh over 150 pounds you're supposed to give 825 milliliters of plasma. Less, and you only give 690 mL. There's another group that has to give 880 mL, but I'm not sure what the weight limit is for that. Probably two hundred.

When I weigh myself at home I register at about 140, maybe 145 pounds. Lightweight, I know, considering I'm like 5'11". But at the plasma place the first day I'm not sure what they weighed me at but I had to give 825 mL. Same with my fourth time. Today I only did 690 again, which was a relief. I think it depends on who weighs you. The scales are the old-fashioned kind (forgive my youth) where you have to slide the 1#, 10# and 100# weights horizontally along the top of it. Might also have something to do with the barometric pressure that day.