I need to roll a tube out of 16 gauge cold rolled sheet steel that is precise in the diam. dimension. The circumference calculation is πDbut to get it very accurate dimension do I use the OD or the ID diameter or for this thin a material does it matter?

For example - the tube needs to be 2.322" in diameter (finished) so the OD of the material would be 3.1415 x 2.322" or 7.294" in width but the ID would be 3.1415 x 2.197" or 6.901" in width. Obviously using the OD or ID matters. The math suggests it would be the OD dimensions but the little I know about sheet metal work tells me it is not that simple. Possibly you would split the difference.

For example - the tube needs to be 2.322" in diameter (finished) so the OD of the material would be 3.1415 x 2.322" or 7.294" in width but the ID would be 3.1415 x 2.197" or 6.901" in width. Obviously using the OD or ID matters. The math suggests it would be the OD dimensions but the little I know about sheet metal work tells me it is not that simple. Possibly you would split the difference.

## Comment