ONE FORMULA, ONE ANSWER
Sheet metal bend allowance calculator
Use an entered K-factor to locate the neutral axis and calculate the developed length of one circular curved bend. Choose input units and calculate one value within the stated conditions.
Inputs
Calculations run in this browser. Scientific notation such as 1.2e-3 is supported. Do not group thousands.
Result
Developed length of the curved bend BA
Enter values and select Calculate.
BA = θ(R + Kt); θ ∈ [0, π] rad
Assumptions
Required: one circular bend with constant thickness, inside radius and K-factor. K is the distance from the inside face to the neutral axis divided by sheet thickness, between 0 and 1. The bend angle is rotation from the flat state, between 0 and 180 degrees, rather than the final included angle. Excluded: straight flange lengths, bend deduction, springback, hemming and thickness change. Use a K-factor measured for the actual material and tooling.
Displayed values are floating-point approximations. Design safety factors and unprovided error contributions are not calculated.
Formula references and credits
NaNa Lab created the code, descriptions, icons and preview images. Text, figures and code from the linked references have not been reproduced.
Physical constants: NIST / CODATA 2022. The values of μ₀ and ε₀ are measured recommendations, not exact defining constants. Values and precision notes are in the source record.
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