How to Calculate GPP (Grains Per Pound) Using Temperature . . . - JustAnswer The GPP (grains per pound) was entered by someone who has a program that calculates the GPP based on the temperature and relative humidity I am not familiar with the physics of it I do know that 7,000 grains equals one pound w = 0 62198 RH 100 PVsat Patm - RH 100 PVsat multiply by 7000 for the grains Habs = (Hsat)(RH 100) = Hsat * (RH 100)