I made up this spreadsheet to calculate coopering angles and stock thickness needed, when making drums, curved containers, barrels etc.

If you know what size cylinder you are after, and the wall thickness you want, this will tell you how thick to cut the staves, how many you need, and what angles to set on the table saw.
Conversely, if you know the stock thickness you have, and you plug in the number of staves, and the angle you set, it'll tell you what size cylinder you'll end up with.

Hopefully others will find it useful.