Sheet Metal Bend Allowance
Bend allowance and flat blank length from K-factor and angle.
Example
You enter
- Thickness (in) 0.06
- Bend angle (deg) 90
- Inside radius (in) 0.125
- K-factor 0.44
- Leg A (in) 2
- Leg B (in) 3
You get
- Bend allowance 0.2378 in
- Flat blank length 4.8678 in
Details, formula, and sources
BA = (π / 180) × angle × (R + K × t) where K is the K-factor (neutral-axis offset) and t is sheet thickness; flat blank = leg1 + leg2 + BA - setback.
Machinery's Handbook by name; SME Sheet Metal Forming by name.
Older Machinery's Handbook editions free at archive.org.
Estimate. AHJ and licensed professional govern.
Field names used by the API: thickness_in, bend_angle_deg, inside_radius_in, k_factor, leg_a_in, leg_b_in, bend_allowance_in, flat_blank_in
- Default K-factor 0.33 (mild steel air bend) unless user suppliesMachinery's Handbook typical