Sheet metal bend allowance & flat length calculator
Work out bend allowance, outside setback, bend deduction, and a planning flat length from thickness, inside radius, bend angle, and K-factor before press brake forming — then send the numbers to FortiFab for quote review.
Flat-pattern results
Updates as you type. FortiFab confirms final bend deductions in review.
Planning flat length
3.885 in
Planning estimate — final production values depend on material, tooling, grain direction, and bend method.
- Bend allowance
- 0.125 in
- Bend deduction
- 0.115 in
- Outside setback
- 0.120 in
Bend inputs
All dimensions are in inches. Results update instantly for a single bend with outside flange dimensions.
Angle the flange is bent through — 90° for a square corner.
Outside flange lengths
Flange A
Flange B
Measured to the outside apex of the bend.
Settings are saved automatically in your browser.
Formula used
Bend allowance = angle in radians × (inside radius + K-factor × material thickness). For a single bend with outside flange dimensions, bend deduction = 2 × outside setback − bend allowance.
OSSB = tan(A / 2) × (R + T)
BD = 2 × OSSB − BA
Flat length = flange A + flange B − BD
These values are planning estimates. Final production values depend on material, tooling, grain direction, bend method, and tolerance stack-up.
Your review summary
Send your DXF, STEP, PDF, or sketch with material, thickness, bend directions, finish, quantity, and delivery city — attach or paste this summary so FortiFab can confirm final bend deductions.
- Material setup
- 0.06" thick · 0.06" inside radius
- Bend
- 90° bend angle
- K-factor
- 0.33
- Flanges
- A 2" · B 2" (outside)
- Bend allowance
- 0.125 in
- Bend deduction
- 0.115 in
- Flat length
- 3.885 in
- Review notes
- None from the current inputs.
Bend allowance forming guide
Plan flat lengths before sending formed sheet-metal parts for review
This calculator helps buyers and designers estimate bend allowance, outside setback, bend deduction, and flat length. Treat the output as a planning aid: FortiFab still reviews material, tooling, grain direction, bend sequence, tolerances, and drawing notes before production.
Common searches
- bend allowance calculator
- sheet metal bend calculator
- bend deduction calculator
- K-factor calculator
Best buyer use cases
- Checking formed brackets, pans, covers, and enclosure flanges
- Estimating flat length before DXF or STEP review
- Flagging bend assumptions for FortiFab quote review
Ready to turn this into a reviewed fabrication quote?
Send drawings, sketches, material, thickness, finish, quantity, and any fit-up requirements so FortiFab can review manufacturability.
Bend allowance FAQs
Planning notes for sheet-metal bend allowance, K-factor, and flat-pattern estimates.
Flat length
3.885 in