Photo courtesy 2005 Lion’s Gate Entertainment

If you have ever seen someone holding a bunch of helium balloons, you may have asked yourself, "How many balloons does it take to actually lift a person off the ground?"

A helium balloon works on the same basic principle as an air bubble in water. A bubble rises in water because it is lighter than the water around it. The water pressure pushes the lightweight bubble upward.

With a helium balloon, what you have is a "bubble" of helium rising in an ocean of air. Helium has a lifting force of about one gram per liter. That happens because helium atoms weigh less than the oxygen and nitrogen atoms in the air.

What this means is simple. If you take a one-liter soda bottle and fill it with helium, it will weigh about one gram less than the same soda bottle filled with air. One gram of lifting power sounds like nothing (a single penny, after all, weighs 3 grams), but the grams can really add up.

If one liter of helium can lift about a gram, and if you weigh 100 pounds, then you are going to need about 45,300 liters of helium to lift yourself off the ground. There are 453 grams in a pound. So the question becomes, "How many balloons does it take to hold 45,300 liters of helium?"

If you buy a balloon at an amusement park, it is normally about one foot in diameter. A balloon like that holds about 14 liters of helium. An amusement park balloon can therefore lift 14 grams or so if you assume that the balloon and the string don't weigh anything. So, using amusement park balloons, you would need 3,235 balloons (45,300 ÷ 14 = 3,235) to lift a 100-pound person. That's a lot of balloons. Plus you would need to add some more to compensate for the weight of the 3,235 balloons and all their strings.

Now, let's say that, instead of going to the amusement park, you go to the army surplus store. You buy a surplus weather balloon that is 4 feet in diameter. A balloon like that can hold about 1,000 liters of helium. With 46 of those balloons, you'd make it off the ground. There is actually a sport called cluster ballooning that takes advantage of balloons this size.

The bigger the balloon, the more it can lift. If you were to buy a huge balloon that is 100 feet in diameter, then you would have some real lifting capacity. A balloon this size holds 14 million liters of helium and can lift 31,000 pounds. A typical elephant weighs about 10,000 pounds. So, this balloon could lift three elephants and still have enough buoyancy so that you could ride along!