Why helium balloons float
A helium balloon floats because it displaces air that weighs more than the helium inside it. At sea level and room temperature, a liter of air weighs about 1.2 g and a liter of helium about 0.17 g, so each liter of helium gives a lift of about 1 gram. The balloon’s own weight, ribbon and any decoration must come out of that.
How the calculator works
- Volume of a round balloon: V = π × D³ ÷ 6.
- Gross lift ≈ 1 g per liter of helium.
- Net lift = gross lift − weight of the empty balloon and ribbon.
- Balloons needed = weight of the object ÷ net lift, rounded up.
- Balloons per tank = tank capacity ÷ volume per balloon.
Latex balloons are not perfect spheres, and they are rarely filled to their full size, so treat the results as estimates.
Example
An 11-inch latex balloon holds about π × 27.9³ ÷ 6 ≈ 11,400 cm³, or 11.4 L. It lifts about 11.4 g, minus 3.5 g for the balloon and ribbon: about 8 g net. To lift a 3.5 oz (99 g) card or small gift, you need about 13 balloons. A 14.9 ft³ tank (422 L) fills about 36 such balloons.
Typical figures
| Balloon | Helium | Approximate net lift |
|---|---|---|
| 9 in latex | about 0.25 ft³ (7 L) | 3 to 4 g |
| 11 in latex | about 0.4 to 0.5 ft³ (11 to 14 L) | 8 to 10 g |
| 16 in latex | about 1.2 ft³ (34 L) | 25 to 30 g |
| 18 in foil | about 0.5 ft³ (14 L) | a few grams |
What reduces lift
- Party-grade helium is often mixed with air, so it lifts less than pure helium.
- Altitude: in Denver, at about 5,300 ft, air is about 17% thinner and lift drops by roughly the same share.
- Cold: balloons shrink in cold air and recover when warmed.
- Leakage: helium escapes through latex. An untreated 11-inch latex balloon floats about 8 to 12 hours; a gel coating can extend that to a day or more, and foil balloons often float for several days.
Safety
- Never inhale helium from a tank or balloon: it can cause loss of consciousness and, from a pressurized tank, serious lung injury.
- Keep balloons away from power lines; foil balloons conduct electricity and cause outages.
- Do not release balloons outdoors: they come down as litter that can harm wildlife, and several U.S. states restrict balloon releases.
- Keep uninflated or broken latex balloons away from young children, who can choke on them.