Bend Allowance Calculator
Calculate bend allowance and the flat blank for one sheet-metal bend before the press brake.
Calculator
About this calculator
This bend allowance calculator is one sheet-metal bend. It does not estimate press-brake tons. Browse the sheet metal calculator hub.
Calculation Results
0.1357 in
Bend allowance · outside setback 0.1200 in · bend deduction 0.1043 in
Formula: BA = (π/180) × angle × (R + K × T)
Flat blank 3.1357 in = inside flanges + bend allowance.
How to use this result
Use the bend allowance when the flange lengths stop at the inside of the bend, and the bend deduction when they are outside dimensions. This is one bend. It ignores grain direction and springback, and it does not tell you press-brake tonnage. Confirm the K-factor with a coupon before cutting a production blank.
Continue Your Calculation
The flat blank does not set a spindle speed. Open speeds and feeds only when the next job is milling or drilling.
Bend allowance examples
Single 90° bend. Click a preset above to load the same inputs.
| Case | Inputs | BA | BD | Flat |
|---|---|---|---|---|
| 16 ga inside | 0.060 in, R 0.060 in, 90°, K 0.44, legs 2 in and 1 in | 0.1357 in | 0.1043 in | 3.1357 in |
| 16 ga outside | Same bend, outside legs 2 in and 1 in | 0.1357 in | 0.1043 in | 2.8957 in |
| 2 mm inside | 2 mm, R 2 mm, 90°, K 0.40, legs 50 mm and 30 mm | 4.398 mm | 3.602 mm | 84.398 mm |
Bend allowance formula
Bend allowance: BA = (π/180) × θ × (R + K × T)
Outside setback: OSSB = tan(θ/2) × (R + T)
Bend deduction: BD = 2 × OSSB − BA
Inside flat: Flat = L1 + L2 + BA. Outside flat: Flat = L1 + L2 − BD.
Example: T = 0.060 in, R = 0.060 in, θ = 90°, K = 0.44. BA = (π/180) × 90 × (0.060 + 0.44 × 0.060) = 0.1357 in. OSSB = 0.1200 in. BD = 0.1043 in. Inside legs 2 in and 1 in give a flat blank of 3.1357 in.
Need spindle RPM after the blank is cut? Use the speeds and feeds calculator. Hub: sheet metal calculator.
Which shop step this is
| Question | Use |
|---|---|
| Flat blank for one bend | This page |
| Milling or drilling RPM and feed | Speeds and feeds calculator |
| Torque at that spindle RPM | Motor torque calculator |
| Horsepower in kilowatts | HP to kW |
Frequently Asked Questions
How do I calculate bend allowance?
Use BA = (π/180) × angle × (R + K × T). Example: 0.060 in thickness, 0.060 in inside radius, 90°, and K = 0.44 gives 0.1357 in.
What is the difference between bend allowance and bend deduction?
Add bend allowance to inside flange lengths. Subtract bend deduction from outside flange lengths. For the 16-gauge example, BD = 2 × 0.1200 − 0.1357 = 0.1043 in.
What K-factor should I use?
Start near 0.33 to 0.50 for an air bend. This page does not look up a material chart. Bend a coupon and replace 0.44 if your die and grain direction differ.
Does this calculator size a press brake?
No. Tonnage depends on thickness, die opening, bend length, and material strength. This page stops at the flat blank.
Is the bend angle the inside angle of the part?
Enter the angle the sheet turns. A square bracket is 90°. The same 90° is not entered as 180°.