Bend Allowance Calculator

Calculate one-bend flat length, allowance, and deduction before laser cutting. Use a shop K-factor or reverse-calculate it from a measured bend allowance.

Bend inputs

Inputs are editable examples. Replace them with your job measurements and shop records.

90° is a right-angle bend; use turn angle, not the remaining inside angle.

Enter your measured or approved shop value, from 0 to 1.

Measure both outside flange dimensions to the virtual sharp intersection of the outside faces. Each must reach at least the outside setback.

Flat pattern

Flat length
3.7611 in
Bend allowance
0.2611 in
Bend deduction
0.2389 in
Outside setback
0.25 in
K-factor
0.33

One ideal bend. Confirm the actual radius and K-factor with a test coupon before releasing a laser-cut blank.

  • Use outside moldline flange dimensions and the angle turned from flat. This single-bend geometry does not predict springback or tooling limits.

Method

Enter the material thickness, finished inside radius, and bend turn angle. Zero turn is flat; a right-angle bend is 90°. Measure outside flange A and B to the virtual sharp intersection of the outer faces. The calculator removes their outside setbacks and adds the neutral-axis arc. In reverse mode, enter a measured bend allowance to infer K-factor for that specific test setup. A measured overall flat length is not the same input as bend allowance.

θ = bend turn angle × π ÷ 180; BA = θ × (R + K × T). Outside setback = (R + T) × tan(θ ÷ 2); BD = 2 × setback − BA. Flat length = outside flange A + outside flange B − BD. Measured K = (measured BA ÷ θ − R) ÷ T.

Worked example

For a 90° turn, 0.125 in inside radius, 0.125 in thickness, K-factor 0.33, and two 2 in outside flange dimensions, bend allowance is approximately 0.2611 in. Outside setback is 0.25 in, bend deduction is 0.2389 in, and flat length is 3.7611 in. The example K-factor is an editable assumption, not a material recommendation.

Limits

This is ideal single-bend geometry. It does not predict springback, achievable inside radius, minimum flange height, bend force, tooling clearance, or a production tolerance. Both outside flange dimensions must reach the calculated setback. K-factor is constrained to 0–1; a measured value outside that range indicates a mismatch in the entered geometry or measurement convention. Confirm the result on a coupon made with the actual material and tooling.