Bend
allowance.
Start with the part.
Find the flat.
Turn your finished dimensions into a flat blank. See the bend allowance, deduction, and developed bend center as you design.
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01 / Design for the bend
From formed part to flat blank.
Start with your finished dimensions. Find the flat length for a single bend, and see where the material goes.
Formed profile
OUTSIDE DIMENSIONSUnfolded blank
ONE CONTINUOUS SHEETUpdate the highlighted inputs
to see your formed part and flat blank.
Estimated flat blank length
A + B − bend deduction
- Bend allowance · BA
- in
- Bend deduction · BD
- in
- Outside setback
- in
- Developed bend center
- in
Length through the bend.
Subtract from A + B.
Tangent to theoretical corner.
From the A-side edge of the blank.
Single-bend geometry estimate. This does not check tooling clearance, minimum flange length, or springback. Confirm your bend data before cutting; the developed center is not a press-brake backgauge setting.
Why the flat is shorter than A + B
Your outside dimensions include the theoretical corner on both legs. Bend deduction removes that overlap and accounts for the developed bend.
Flat length = A + B − BDThe math behind the result
θ is the bend from flat in degrees. An inside opening of 120° means a 60° bend from flat.
BA = (π / 180) × θ × (R + K × T)
Setback = (R + T) × tan(θ / 2)
BD = 2 × setback − BAMore than one bend?
Build the complete profile in our simulator.
How should I measure legs A and B?
Use the finished outside dimensions from each free edge to the theoretical sharp intersection of the two outside faces. Do not enter the straight distance to the start of the radius. For straight tangent lengths, the relationship is different: flat length = straight A + bend allowance + straight B.
Which K-factor and radius should I use?
Use measured values or a validated bend table for the material, thickness, tooling, and forming process you will use. A generic material name does not determine either value. The example starts at K = 0.42 so you can explore the calculation; it is not a guarantee for a specific alloy. Read our bending guide ↗
What is the difference between bend angle and inside opening?
A bend from flat measures how far the sheet rotates away from a straight sheet. The inside opening is the angle between the finished legs. They add to 180°. Both are 90° for a right-angle bracket. Switching the angle convention here keeps the same part and converts the number for you.
Develop the blank.
Make the part.
Bring your finished dimensions and validated bend data to your next design.
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