5 min read
How much helium do I need?
Count the balloons, multiply by the helium each one takes, and buy the cylinder above that number. The arithmetic is easy — it is the balloon sizes that catch people out.
Helium per balloon
A 9 inch latex takes about 0.0065m³ of helium. A 10 inch takes 0.009m³. A 12 inch takes 0.0158m³ — nearly two and a half times the 9 inch, for a balloon that only looks a bit bigger.
An 18 inch foil takes around 0.015m³, so about the same as a 12 inch latex. Giants are in another category entirely: a 2ft latex takes 0.111m³ and a 3ft takes 0.227m³. One 3ft giant uses the same gas as twenty-five 10 inch balloons.
Matching that to a cylinder
Cylinders are sold by volume in cubic metres, so divide the cylinder by the figure for your balloon. A 1.81m³ cylinder fills about 278 balloons at 9 inch, or 114 at 12 inch.
Disposable canisters are named for the number of 9 inch balloons they fill — a "Disposable 100" holds 0.7m³ and fills 100 at 9 inch. Fill 12 inch balloons from it instead and you will get roughly 44.
Where people go wrong
The commonest mistake is buying for the balloon count without checking the size. The second is over-inflating, which uses more gas per balloon than the figures above and can cut a cylinder's real-world yield by a fifth.
The third is forgetting the giants. If your plan has two 3ft balloons in it, that is 0.45m³ before you have filled a single small one.
Buy the next size up if you are close to a boundary. Running out halfway through decorating a venue costs more in stress than the difference in cylinder price.
Common questions
- Is hire or disposable cheaper?
- Disposables are simpler and cheaper below roughly 150 balloons. Above that, hire is cheaper per balloon and the gap widens quickly. At 500 balloons hire is not close.
- Can I use leftover gas later?
- From a hire cylinder, yes — it holds pressure fine until you return it. From a disposable, no. Use it the same day; the valve is not built to hold gas over weeks.