How can I measure the volume of a balloon? I'm working on a project and I need to measure the volume of a balloon. In fact, I need to measure its radius. I want you to give me advice and ways of measuring it.
 A: If you assume that the balloon is spherical you can fill a bucket completely with water,  gather the volume it displaced and measure it.  Then you use the formula $V=\frac43\pi r^3$ to get the radius.
To do this i am assuming that the compression of the balloon is negligible when it is underwater. 
A: Fill the Balloon with water instead of Air, and use the Water volume
displacement method in the prior answer.
A Displacement cylinder that is either rectangular, or, a Cylinder
is far easier to calculate volume change, with and without the 
water balloon.
A short piece of smooth walled large diameter plastic water pipe,
with a homemade flat bottom would work well. Plywood disc glued 
into the cylinder with silicone sealer ( adhesive ), and varnished
to make it waterproof inside.
A 6 inch by 12 inch concrete testing cylinder would also work, as the
diameter is then known.
Mike Clark
Golden, Colorado, USA
A: You can do sth better :
1 - first inflate the balloon and then deflate it to a spherical shape (Because usually ,balloons aren't spherical shape and this is the matter of this question.) 
