Sheet metal

Bend Deduction Calculator

Estimate the bend deduction — the amount subtracted from the sum of outside flange lengths to get the flat blank. Use this when the part is dimensioned to outside flanges.

mild steel16 ga0.0598 in1.519 mm

Interactive calculator

Bend Deduction Calculator

MaterialGaugeThickness

Inside radius

Bend angle

deg

K-factor

Bend deduction0.1058 in

Bend allowance0.1334 in

Assumptions

Verify before production

Calculator values are estimates. Confirm bend deductions, springback, tooling, grain direction, coating condition, and safe tonnage with the material and tooling supplier before production.

Air bending and common gauge tables are assumed unless edited.
Actual results vary by tooling, grain direction, coating, temper, and springback.
Machine capacity and tooling load ratings must be checked independently.
Result is a screening estimate for shop planning. Verify against material certificate, tooling chart, machine rating, and a coupon test before production.
Math is for bend angles strictly less than 180°. Hemming and special forming need process-specific data.
Springback is not included; measure the final angle after release, not at the bottom of the stroke.

Default material and formula constants are documented at /reference/data-sources/.

Static reference

Common thickness, radius, and angle combinations

Swipe table horizontally for more columns.

Gauge	Thickness	Inside radius	Angle	Bend allowance	Bend deduction
16 ga	0.0598 in / 1.519 mm	0.0598 in / 1.519 mm	45 deg	0.0667 in	0.0324 in
12 ga	0.1046 in / 2.657 mm	0.1569 in / 3.985 mm	90 deg	0.3155 in	0.2075 in

Formula used

What this calculator computes

OSSB = tan(A / 2) × (r + t)

OSSB: Outside setback (one side) (in or mm)
A: Bend angle (rotation angle, degrees) (deg)
r: Inside bend radius (in or mm)
t: Material thickness (in or mm)

Bend angle A is the angle of rotation through which the sheet is bent (the supplement of the included angle for less-than-180° bends). A flat sheet bent so its flanges meet at 90° corresponds to A = 90°. If your drawing labels the included angle, convert with A = 180° − included angle before entering it.

BD = 2 × OSSB − BA

BD: Bend deduction (in or mm)
OSSB: Outside setback (per side) (in or mm)
BA: Bend allowance (in or mm)

Flat length = (sum of outside flange lengths) − BD per bend.
Use bend allowance instead when your dimensions are inside-flange or neutral-axis based.

Worked example

One numeric walk-through

Inputs

Thickness t: 0.0598 in
Inside radius r: 0.0598 in
Bend angle A: 90°
K-factor: 0.42

Steps

OSSB = tan(45°) × (0.0598 + 0.0598) = 1 × 0.1196 = 0.1196 in.
BA = (π/2) × (0.0598 + 0.42 × 0.0598) ≈ 0.1334 in.
BD = 2 × 0.1196 − 0.1334 ≈ 0.1058 in.

Result

Bend deduction ≈ 0.1058 in. Subtract this from the sum of outside flange lengths to get the flat blank.

Common mistakes

Things to check before trusting the number

Mixing bend deduction with inside-flange dimensions. Use bend allowance for inside-flange dimensions.
Treating included angle as bend angle — for any non-90° bend the OSSB term changes substantially.
Using bend deduction on hems, acute coined bends, or radii smaller than the material's minimum bend radius.
Forgetting that bend deduction is per bend; subtract it once for every bend in a multi-bend part.

FAQ

Specific checks for this calculator

When should I use bend deduction instead of bend allowance?

Use bend deduction when your part is dimensioned to outside flange lengths. Subtract the deduction from the sum of those flanges to get the flat blank.

Does bend deduction work for any angle?

It works for bend angles less than 180°. Hems, acute coined bends, and special tooling need process-specific data instead.

Bend Deduction Calculator

Bend Deduction Calculator

Common thickness, radius, and angle combinations

What this calculator computes

One numeric walk-through

Inputs

Steps

Result

Things to check before trusting the number

Move between connected shop calculations

Specific checks for this calculator

When should I use bend deduction instead of bend allowance?

Does bend deduction work for any angle?