Bend Allowance & K-Factor.
Calculate flat blank size for sheet metal press brake forming. Bend allowance, bend deduction, K-factor, and outside setback for any angle, thickness, and inside radius.
Auto-loads typical K-factor. Always verify with a test bend.
mm
mm — typically equals thickness for most press brakes
degrees — angle of bend (90° = right angle)
0 to 0.5 — neutral axis position. Default 0.42 for mild steel.
mm — outside dimension
mm — outside dimension
FLAT BLANK LENGTH
—
mm — leg A + leg B − bend deduction
Bend Allowance (BA)
—
Bend Deduction (BD)
—
Outside Setback (OSSB)
—
Neutral axis offset
—
BA = (π/180) × α × (R + K·T)
OSSB = tan(α/2) × (R + T)
BD = 2·OSSB − BA
Flat = A + B − BD
OSSB = tan(α/2) × (R + T)
BD = 2·OSSB − BA
Flat = A + B − BD
Typical K-factor reference
| Material | Soft (R<T) | Medium (R≈T) | Hard (R>2T) |
|---|---|---|---|
| Mild steel — CRCA | 0.33 | 0.42 | 0.50 |
| Mild steel — HR | 0.38 | 0.45 | 0.50 |
| Stainless steel 304/316 | 0.40 | 0.45 | 0.50 |
| Aluminium — soft (5052, 6061-O) | 0.33 | 0.40 | 0.45 |
| Aluminium — hard (6061-T6) | 0.38 | 0.42 | 0.50 |
| Copper / brass — annealed | 0.35 | 0.40 | 0.45 |