Balloon Helium Calculator

Helium balloons float because helium is lighter than air. The volume of helium needed depends entirely on the size of the balloon being inflated.

Volume of helium per balloon by size:

Common helium tank sizes:

Tips for longer float times:

• Use Hi-Float, a rubberizing solution swirled inside the balloon before you inflate it. The maker claims up to 25 times the float life, and in a cool indoor room a treated 11-inch latex balloon really will still be up two days later
• Avoid inflating in extreme heat or cold, because balloons expand in heat and shrink in cold
• Mylar / foil balloons float 3–10× longer than latex at the same size
• Tie balloons securely. A loose knot leaks helium quickly
• Do not overinflate. The balloon should feel firm but not taut, and an overinflated one pops sooner and floats for less time

One thing tank ratings do not tell you. A tank is rated by the gas it holds at full pressure, and you cannot get the last of it out: the flow slows to nothing while there is still gas in the cylinder. Party City rates its 8.9 cu ft disposable at 30 balloons of 9 inches, where the arithmetic on this page says 35. Plan for roughly 85% of the number below, or buy the next size up if the count has to be exact.

Note about outdoor vs indoor:

Outdoor balloons in summer heat may expand and pop before the event. Inflate 10–15% under full capacity for outdoor summer events.