What this calculator does
Sheet metal bend allowance works out flat pattern length added by a bend, from thickness, radius, angle and the K-factor. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaBend allowance = angle(rad) × (inside radius + K × thickness)
The inputs explained
| Field | What to enter |
|---|---|
| Bend angle (°) | A number, measured in °. Starts at 90. |
| Inside bend radius (mm) | A number, measured in mm. Starts at 3. |
| Material thickness (mm) | A number, measured in mm. Starts at 2. |
| K-factor | A number. Starts at 0.44. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with bend angle
Every other input is held at the calculator’s starting values while bend angle varies. Select any row to load that scenario into the calculator.