Your Sheet Metal Bend Allowance & K-Factor
Calculate sheet metal bend allowance, bend deduction, outside setback and flat blank length for multi-bend parts, with K-factor starting values by material.
- Free to use
- No signup
- Nothing to install
- Runs in your browser
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The Sheet Metal Bend Allowance & K-Factor with sample data entered and the result showing.
What is the Sheet Metal Bend Allowance & K-Factor?
When sheet metal is bent, the inside compresses and the outside stretches, and a neutral line stays the same length. The bend allowance is the length of that neutral line in the bend: BA = θ·(R + K·t), where θ is the bend angle in radians, R the inside radius, t the thickness and K the K-factor (the neutral axis position as a fraction of the thickness). From it follow the bend deduction (BD = 2·OSSB − BA), the outside setback (OSSB = (R + t)·tan(θ/2)) and the flat blank length of a part with several bends.
The first tab computes BA, BD, setbacks and the neutral radius, estimating K from the R/t ratio if you leave it at zero. The second builds a flat pattern from the outside leg lengths and bend angles of up to ten flanges. The third derives your actual K-factor from a test piece — bend a blank, measure its outside legs and the original flat length — which removes the guesswork for your brake, tooling and material.
3 steps to your result
Open the tool and follow along. Nothing to install.
What you get
All the standard bend quantities for any angle and radius.
Up to ten flanges with individual angles.
Calculate K from a measured test bend.
K-factor table by R/t and material hardness; minimum radius guidance.
AZRS tools are free to open and use.
It opens in your browser, so there is nothing to download.
Used for
Pick one to see how it fits.
Sheet-metal students and designers
Flat-pattern calculations for CAD and drawings.
Try it freeHow it compares
A plain look at this tool next to the usual alternative.
| This engineering calculator | Desktop software | |
|---|---|---|
| Install | Nothing to install | Usually an app or program to install |
| Account | No signup | Depends on the product |
| Cost | Free to use | Free or paid, depends on the product |
| Where it runs | In your browser tab | On your computer |
Questions people ask
What is the K-factor?
The ratio of the neutral axis distance from the inside surface to the thickness (0 to 0.5).
Bend allowance vs deduction?
Allowance is the neutral-line length in the bend; deduction is subtracted from the sum of outside legs.
What angle do I enter?
The angle the material is bent through (90° for a right angle).
Is it exact?
It follows the standard formulas; real parts depend on K, which you can calibrate.
How do I use the Sheet Metal Bend Allowance & K-Factor?
1. Enter thickness, inside radius and angle. 2. Use the estimated K or enter your own. 3. Build the flat length in the Flat pattern tab. 4. Calibrate K with a test bend if tolerances are tight.
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Bend allowance, bend deduction, setback, flat length and K-factor from a test bend. Free to use.
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