Enter fabrication inputs
Sample fabrication scenarios
| Material | Thickness | Angle | Inside Radius | K-Factor | Bend Allowance | Flat Length |
|---|---|---|---|---|---|---|
| Cold Rolled Steel, Annealed | 1.0 mm | 90° | 1.0 mm | 0.33 | 2.0892 mm | 78.0892 mm |
| Cold Rolled Steel, Mild | 1.5 mm | 90° | 1.8 mm | 0.38 | 3.7228 mm | 82.1228 mm |
| Aluminum 5052, H32 | 2.0 mm | 120° | 1.6 mm | 0.40 | 5.0265 mm | 97.5558 mm |
| Stainless Steel 304, Half Hard | 3.0 mm | 135° | 6.0 mm | 0.42 | 17.1060 mm | 108.6501 mm |
Core equations behind the calculator
Inside Radius = Thickness × Material Multiplier
Outside Radius = Inside Radius + Thickness
Neutral Radius = Inside Radius + (K-Factor × Thickness)
Bend Allowance = (π ÷ 180 × Bend Angle) × Neutral Radius
Outside Setback = tan(Bend Angle ÷ 2) × (Inside Radius + Thickness)
Bend Deduction = 2 × Outside Setback − Bend Allowance
Flat Length = Flange A + Flange B − Bend Deduction
Blank Area = Flat Length × Part Width
Simple workflow for site and shop planning
- Choose the unit system you use on drawings or fabrication sheets.
- Select the sheet material and temper to load a practical preset multiplier.
- Enter thickness, bend angle, flange dimensions, part width, and K-factor.
- Pick a radius method. Use preset, custom factor, or direct inside radius.
- Click the calculate button to display the result block above the form.
- Review the radius status, bend allowance, bend deduction, and flat length.
- Use the chart for quick comparison of geometry and development values.
- Download the current run as CSV or PDF for estimating, checking, or shop handoff.
Common questions
1) What is sheet metal bend radius?
It is the radius formed at the inside face of a bend. It affects cracking risk, bend allowance, tooling choice, and the final flat length used before fabrication.
2) Why does the calculator use inside radius?
Inside radius is the standard reference for most bend calculations. Once it is known, outside radius, neutral radius, allowance, and deduction can be derived consistently.
3) How do I choose a K-factor?
Use your shop standard, tooling data, or test bends. Many air-bend jobs fall between 0.30 and 0.50, but the correct value depends on material, tooling, and process control.
4) What does bend allowance mean?
Bend allowance is the arc length of the neutral axis through the bend. It helps convert formed dimensions into a flat pattern for cutting or nesting.
5) What is bend deduction used for?
Bend deduction adjusts flange sums back to a flat blank length. It is useful when drawings list outside flange dimensions and you need the pre-bend size.
6) Can I use this for flashing, trims, and duct accessories?
Yes. It is helpful for construction sheet metal tasks such as flashings, covers, trays, trims, and light duct accessories where quick flat-length checks matter.
7) Is the preset radius always correct?
No. Presets are practical starting points. Final values should be confirmed against tooling, supplier data, bend tests, tolerances, and any internal fabrication standards.
8) Why might my flat length differ from shop results?
Differences can come from tooling geometry, springback control, grain direction, actual temper, machine setup, and the K-factor used in your production environment.