Bend Allowance K-Factor Formula
Bend allowance and K-factor are tied together: K places the neutral axis, and bend allowance is the arc length of that neutral axis through the bend.
bend allowance k factor bend allowance formula k-factor inside radius k-factor
The relationship
For one bend, bend allowance is the developed arc length of the neutral axis. The K-factor says how far that neutral axis sits from the inside bend surface.
BA = theta * (R + K * t)
What each symbol means
- theta: bend angle in radians.
- R: inside bend radius.
- t: material thickness.
- K: neutral-axis offset divided by thickness.
Worked example
For a 90 degree bend, R = 3 mm, t = 2 mm and K = 0.33: BA = 1.5708 * (3 + 0.33 * 2) = 5.75 mm.
Related pages
- Sheet-metal K-factor calculator - back-solve K from a measured bend allowance or coupon.
- Bend allowance calculator - use a known K-factor to calculate bend allowance.
- Bend deduction calculator - convert between outside dimensions and flat length.
- What is K-factor? - neutral-axis explanation and formula context.