Most sheet metal materials will conform to the calculations.
Bend allowance formula in sheet metal.
Lf l1 l2 ba.
The following illustration shows the equation calculation for determining the bend allowance when forming sheet metal.
This page also includes a link to a on line sheet metal bend allowance calculator.
Where ba is bending allowance.
The total length of the flatten sheet is equal to the sum of l1 that s the first length and l2 plus the bend allowance.
You will need to know your material thickness mt the bend angle b the inside radius ir and the k factor k.
If you have a sheet metal bending product as shown in above picture with two legs of length x and y and you unbend it you will see that total length of the unbend sheet will not x y rather the length will be x y ba.
The bend allowance region is shown in green in my diagram this is a region wherein theory all deformation occurs during the bending process.
The material thickness will be measured in decimal form not by the gauge number.