Sheet Metal Bend Allowance

A sheet metal calculator for the flat pattern of a bent part. Enter thickness, inside radius, bend angle and K factor, and get bend allowance, bend deduction, outside setback and the flat length before you cut — with a profile diagram that shows exactly which dimensions you entered.

Built for sheet metal shops, HVAC duct fabricators and anyone who runs a press brake and is tired of redoing the math on scrap paper.

Key Features

- Bend allowance calculator: BA = θ × (R + K × T), with outside setback and bend deduction shown next to it.
- Single bend, L, U and Z profiles: enter outside flange dimensions and get the flat length with every bend deduction applied.
- Outside dimensions made clear: the diagram labels each flange as an outside (outer mold line) dimension, so inside and outside measurements don't get mixed up.
- Bend direction on the drawing: U channels bend the same way twice, Z profiles bend up then down — both show on the profile and on the flat pattern.
- Flat pattern with bend lines: see where each bend line falls from the left edge of the blank for layout.
- K-factor starting values: pick aluminum, mild steel or stainless and a starting K is filled in from the R/T ratio. Enter your own K when you have tested it.
- Cut length rounded up: the exact flat length and a rounded-up cut length (0.5 mm or 1/32 in) are shown separately.
- Project parts list: add parts with quantities, duplicate or delete them, and copy the whole list with the inputs behind each line.
- mm or inches: switch units at any time; comma decimals work too.
- Recent projects: save up to 20 projects on the device and reopen one as a new job.

Recommended For

- Press brake operators checking a blank size before cutting
- HVAC and duct fabricators laying out brackets, channels and Z flashing
- Students learning bend allowance and bend deduction

The K-factor table gives starting values only, and springback is not included. Results are planning values — make a test bend before cutting production parts. The app does not export DXF or PDF and does not calculate press brake tonnage.