Balloon (Helium) Calculator
Calculate how much helium you need for the number of balloons and balloon size you're planning for the party.
How to use the calculator
- Enter how many balloons you're filling.
- Enter the diameter you plan to inflate each balloon to.
- See the total helium volume you need — match this against the liter rating on the helium tank you buy.
How it's calculated
An inflated balloon is approximately spherical, so volume is calculated with the standard sphere formula. Total helium needed is the volume per balloon times the number of balloons. Note that diameter has a big effect — a balloon twice as large needs eight times as much helium (2³ = 8), not just double.
Helium leaks straight through the balloon wall
Helium atoms are very small, and latex has microscopic pores that the atoms gradually pass through. That is why a latex balloon sinks after a few hours even when it is tied perfectly tight. Foil balloons last considerably longer because the metallised film is far less permeable — they can stay afloat for days or weeks.
Temperature also affects buoyancy noticeably. Bring balloons from a cold car into a warm room and the gas expands, making them look firmer; go the other way and they shrink and can seem half filled. If the balloons are for outdoor use on a cold day, it is worth inflating them slightly rounder than the finished look you want.
Frequently asked questions
Why does a slightly bigger balloon need SO much more helium?
Because volume grows with the cube of the radius, not linearly. A balloon with double the diameter has eight times the volume — an often-underestimated effect.
How long does a helium balloon float?
Standard latex balloons typically float for 8-12 hours, while foil (mylar) balloons can float for several days since they leak less helium through the material.
How much helium is in a typical disposable tank?
It varies a lot between products — always check the liter rating on the tank you're buying, and use the calculator's total to check whether it's enough.