Fabrication

Sheet Metal Bend Calculator

Calculate bend allowance, deduction, and flat pattern length for sheet metal fabrication.

Input Parameters

Units:

Material Type

Material Thickness

Inside Bend Radius

Bend Angle

degrees

Optional: Enter flange lengths to calculate flat pattern length

Flange A (outside dimension)

Flange B (outside dimension)

Results

Enter bend parameters and click Calculate

What is a Sheet Metal Bend Calculator?

A sheet metal bend calculator determines bend allowance, bend deduction, and flat pattern length for press brake operations based on material thickness, bend radius, and angle.

Accurate flat pattern calculations ensure parts fit together correctly after bending, avoiding costly material waste and rework.

How to Use

Select material type or enter custom K-factor
Enter material thickness
Enter inside bend radius (from tooling)
Enter bend angle (90° is most common)
Optionally enter flange dimensions for flat length
Click Calculate for bend allowance and deduction

FAQs

K-factor is the ratio of the neutral axis location to material thickness (0 = inside surface, 0.5 = center). Typical values: 0.33 for soft materials/large radius, 0.38-0.45 for harder materials/tight bends. Best practice: make test bends and back-calculate K from measured flat length.

Bend Allowance is the arc length of the neutral axis - add it to inside leg dimensions. Bend Deduction is what to subtract from outside dimension sum. Both methods give the same flat length when used correctly with their corresponding dimension system.

Minimum inside bend radius is typically 1× material thickness for soft aluminum, 1.5× for cold-rolled steel, and 2× or more for stainless or hard tempers. Tighter bends cause cracking on the outside surface. Air bending allows slightly tighter radii than bottoming.

Common causes: wrong K-factor for your material/tooling, measuring inside vs outside dimensions inconsistently, not accounting for springback, or tool wear affecting actual bend radius. Make test parts and measure actual results to calibrate your K-factor.

Springback causes material to 'spring back' toward its original shape after bending. Compensate by overbending: 1-3° for soft steel, 5-10° for stainless or spring steel. Bottom bending reduces springback vs air bending. VFDs with angle sensors can auto-compensate.

Limitations

• K-factor varies with tooling - test to determine actual value
• Does not account for springback - add overbend as needed
• Assumes uniform material properties throughout
• Results are theoretical - verify with test bends
• Complex parts may need CAD software for accurate unfolding