How can I quickly and easily size my balloons?

Sizing Cube

Foldable Balloon Sizer 

Balloon Sizers are a great way to quickly size your balloons.  This is especially true if you need to work quickly.  As well, if you are constructing a 3D balloon sculpture, and need specifically sized balloons, this is also a very convenient tool to have. 

Balloons Online sells both a sizing cube, which is lightweight and easy to carry around, and a foldable balloon sizer as well.