You will need to know your material thickness mt the bend angle b the inside radius ir and the k factor k.
Bend allowance formula in sheet metal.
Lf l1 l2 ba.
Most sheet metal materials will conform to the calculations.
Where ba is bending allowance.
The bend allowance region is shown in green in my diagram this is a region wherein theory all deformation occurs during the bending process.
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 formula takes into account the geometries of bending and the properties of your metal to determine the bend allowance.
The following illustration shows the equation calculation for determining the bend allowance when forming sheet metal.
The material thickness will be measured in decimal form not by the gauge number.
Ba bend allowance.