Helium Balloon Lift Calculator: How Many Balloons to Lift a Weight?

How it works

Lift per liter = purity × (ρ_air − ρ_gas), with ρ = P × M ÷ (R × T) · M_air = 28.965 g/mol, M_helium = 4.003 g/mol, M_hydrogen = 2.016 g/mol, R = 8.3145 J/(mol·K) · P = 101,325 Pa × (1 − 2.25577 × 10⁻⁵ × altitude in m)^5.25588 · balloon volume = 4/3 × π × (diameter ÷ 2)³ · lift per balloon = volume × lift per liter − balloon weight · balloons needed = weight ÷ lift per balloon, rounded up

A helium balloon floats because it pushes aside its own volume of air, and that air weighs more than the helium inside (Archimedes’ principle). The difference is the lift: about 1 gram for every liter of helium at room temperature and sea level, or roughly 1 ounce per cubic foot. The calculator works it out from the gas law instead of using a fixed number, so it can follow the temperature and the thinner air at altitude: at 68 °F (20 °C) and sea level, air weighs 1.204 g/L and helium 0.166 g/L, leaving 1.038 g of lift per liter. A standard 11-inch party balloon holds 11.4 liters, so it lifts about 11.9 g, under half an ounce, before you subtract the balloon and ribbon. Pick “Balloons needed” to see how many balloons a weight takes, or “Lift of my balloons” to see what a bunch can carry. A table compares every common balloon size, and under More options you can subtract the weight of each balloon and ribbon, lower the gas purity (party-tank balloon gas is often mixed with air) or switch to hydrogen for comparison. The result assumes perfectly round balloons filled to the size you enter; real balloons are often a bit smaller and leak helium over time, so plan a few spares. Unlike the general buoyancy calculator, which works with any object and fluid, this one is built around balloon sizes and counts; the balloon garland calculator counts balloons for decorations rather than lift.

Worked example

To lift 100 g with 11-inch helium balloons at 68 °F and sea level: air density is 101,325 × 28.965 ÷ (8.3145 × 293.15) = 1.2041 g/L and helium density is 0.1664 g/L, so the lift is 1.0377 g per liter. An 11-inch balloon has a radius of 13.97 cm and a volume of 4/3 × π × 13.97³ = 11.42 L, so it lifts 11.42 × 1.0377 = 11.85 g. You need 100 ÷ 11.85 = 8.44, rounded up to 9 balloons, holding 3.63 cu ft (102.8 L) of helium in total with 6.6 g of lift to spare.

Sources: Omni Calculator: Helium balloons (balloon sizes, 75 kg example, 1 kg FAQ) · Interesting Engineering: How many helium balloons to lift anything (densities, 1 g per liter) · Smithsonian National Air and Space Museum: Lighter than air

Frequently asked questions