How much helium does it take to fill a 16 ft. balloon?

Answer 1

Enrique_C is correct if there is no stretch in the balloon's material, like with a Mylar balloon. With a latex balloon, it would take more helium, because it requires more pressure to stretch the balloon material. This pressure will increase the density of the helium in the balloon, thus requiring more helium to fill the same space. The smaller the balloon is when deflated, the more helium it will take to inflate it to 16ft.

Answer 2

(4/3)pi(r^3) is the volume of a sphere, so if Diameter is 16ft, r=8, and V = 2144 cubic feet, at 0.011 pounds per cubic foot (He density), that would be 23.6 pounds.