QUESTION #224

# If I know the diameter of a balloon can I find it's volume?

Asked by: Henry Wherry

### Answer

Yes! If you know the diameter of anything that has the shape of a sphere you can calculate its volume. I am sure you know the equation is (4/3)**r3. In other words if you know the diameter you could take half of it, the radius, cube it multiply it by pi and then multiply by 4 and divide the whole thing by three and you will have the volume of the sphere.

Will this work for a balloon? I do not think so! Most balloons are not perfect spheres. You could get a good approximation for its volume and if your work does not require perfect accuracy using this equation could work well for you.

But, if you really need a good accurate number for the volume of the balloon there are other ways to measure its volume. You could fill a container with water and place the balloon under the water and measure how much water the balloon displaces. This method would give you a good number but it might be a little less than the actual volume of the balloon in air since the water would compress the balloon. Another way to measure the volume is to first decide what you want the volume to be then get a container of that volume, put the balloon into the container and fill the balloon with air until it fills the container. For example, if you wanted a two liter balloon you could place the balloon into an empty two liter soft drink bottle. Of course you will have to first put a hole in the bottom of the bottle so that as you fill the balloon with air the air in the bottle can escape. Also, you would probably have to cut the balloon out of the bottle once you filled it with air.
Answered by: Tom Young, M.S., Science Teacher, Whitehouse High School, Texas