Why does a bag of cement weigh 94 pounds?

Answer 1

The weight of a 94 lb. sack of cement is incidental - the bag is packaged in that size in order to hold one cubic foot of cement, and 94 pounds is simply what one cubic foot of dry cement powder weighs.

Mix design for concrete was originally performed by volume and not by weight. Mix designers were initially concerned about variations in density and thought volume would deliver the most consistent results. As time progressed, they found that mix design were not adversly affected when designed by weight, (which was also much simpler), and therefore became used industry wide. Because 94lbs of cement is, as noted above, what 1 cubic foot of cement weighs, the 94 lb sack was a backhanded way for the mix designers to check the weight calculations easily with known volumes.