If you only know the volume, you can't.

You need to know a couple things... The volume and the height for example.

The volume is equal to the area of the base multiplied by the height, so if you have the volume and the height you get

V (volume) = A (area) * H (height)

or

V / h = A

Once you know the area of the base, you can solve for the radius with

A = π (r)

or √(A/π) = r

You need to know a couple things... The volume and the height for example.

The volume is equal to the area of the base multiplied by the height, so if you have the volume and the height you get

V (volume) = A (area) * H (height)

or

V / h = A

Once you know the area of the base, you can solve for the radius with

A = π (r)

^{2}or √(A/π) = r

^{}