How this calculator works
Each balloon’s helium requirement depends on its inflated volume, which is calculated from its diameter using the sphere volume formula. Multiplying by the number of balloons gives the total helium volume needed, which is then divided by your tank’s rated capacity to estimate how many tanks to buy.
The formulas
Balloon volume = 4/3 × π × radius³. Lift per balloon uses the standard approximation that helium provides about 1.07 grams of lift per liter of gas (the density difference between air and helium).
Real-world fills vary with altitude, temperature, and balloon stretch, and party-store tanks often under-deliver their rated volume. Buy a little extra helium as a buffer, especially for larger events.
Last reviewed August 2026