|How do you calculate how much weight a helium balloon can lift? - C & S
A helium balloon experiences an upward force that is equal to the weight of the air it displaces (the buoyant force on the balloon) minus its own weight. At sea level, air weighs about 0.078 pounds per cubic foot, so the upward buoyant force on a cubic foot of helium is about 0.078 pounds. A cubic foot of helium weighs only about 0.011 pounds. The difference between the upward buoyant force on the cubic foot of helium and the weight of the helium is the amount of extra weight that the helium can lift, which is about 0.067 pounds per cubic foot. To lift a 100 pound person, you'll need about 1500 cubic feet of helium in your balloon.