Sheet-metal bend and flat-length calculator
A preliminary geometric flat pattern for one bend. Enter verified radius and K-factor values; the starting numbers are an example only.
Geometric estimate
- Flat length L
- 96.027 mm
- Bend allowance BA
- 5.027 mm
- Bend deduction BD
- 3.973 mm
- Outside setback SB
- 4.50 mm
Results update as you type. Starting values are an example, not a material or tooling recommendation. Verify before production.
Sketch and dimensions
Example section at α = 90°, not to scale. The sketch explains the dimensions and does not change with the input values.
- S
- Virtual intersection of the outside faces: a and b are measured to this point.
- Neutral axis
- Neutral axis — at a distance K × t from the inside surface. R is the inside radius and α is the inside angle.
How to measure the inputs
a and b are outside flange dimensions measured to the virtual intersection of their straight outer faces, not to the bend tangencies. α is the final inside angle: 90° for a right angle and 180° for a flat sheet.
K-factor method
K is the distance from the inside surface to the neutral axis divided by thickness t. We use θ = (180 − α) × π / 180 in radians and inside radius R.
- Neutral-axis bend allowance: BA = θ × (R + K × t).
- Outside setback to the tangent: SB = (R + t) × tan(θ / 2).
- Bend deduction: BD = 2 × SB − BA.
- Flat length: L = a + b − BD. Each flange must be at least SB.
Use production-specific data
Choose the radius and K-factor from a validated bend table or trial bend for the actual material and tooling. This calculator is not a DIN 6935 compliance check and does not infer the radius automatically from the die opening.