K-Factor Calculator
Use this K-factor calculator to estimate sheet metal bend allowance or K-factor from bend angle, thickness, inside radius, and bend allowance. It is a practical fabrication tool when you want to compare a bend layout before cutting metal.
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Quick Answer:
The K-factor describes where the neutral axis sits in a bend. A common relationship is K = (180 x bend allowance) / (pi x bend angle x thickness) - (inside radius / thickness). If you already know the K-factor, you can also solve for bend allowance with the same inputs.
What This K-Factor Calculator Helps You Do
Use this K-factor calculator to estimate sheet metal bend allowance or K-factor from bend angle, thickness, inside radius, and bend allowance. It is a practical fabrication tool when you want to compare a bend layout before cutting metal.
How to Calculate K-Factor Calculator
- Enter the sheet thickness - Use the actual sheet thickness for the bend calculation.
- Add the radius and angle - Enter the inside bend radius and the angle of the bend.
- Choose what to solve for - Pick K-factor or bend allowance depending on which value you already know.
- Compare with your shop practice - Use the result as a layout check before cutting and bending the part.
K-Factor Calculator Formula
K = (180 x bendAllowance) / (pi x bendAngle x thickness) - (innerRadius / thickness) | Bend allowance = (bendAngle x pi / 180) x (innerRadius + K x thickness)
| Symbol | Definition | Unit |
|---|---|---|
| thickness | Sheet thickness | mm |
| innerRadius | Inside bend radius | mm |
| bendAngle | Bend angle | deg |
| bendAllowance | Bend allowance | mm |
| kFactor | K-factor | - |
Worked Examples
USA - 90 degree bend
- thickness: 2.0
- innerRadius: 1.5
- bendAngle: 90
- bendAllowance: 3.0
- kFactor: 0.33
Result: K-factor = 0.20
This is a common setup check for a simple shop bend. The estimate is 0.20 .
UK - Known K-factor
- thickness: 1.6
- innerRadius: 1.2
- bendAngle: 90
- bendAllowance: 2.5
- kFactor: 0.38
Result: Bend allowance = 2.84 mm
Use the K-factor you already know to estimate the bend allowance. The estimate is 2.84 mm.
EU - Thicker sheet bend
- thickness: 3.0
- innerRadius: 2.0
- bendAngle: 120
- bendAllowance: 7.0
- kFactor: 0.4
Result: K-factor = 0.45
A thicker sheet and larger angle change the neutral axis position. The estimate is 0.45 .
GCC - Fabrication layout check
- thickness: 2.5
- innerRadius: 1.8
- bendAngle: 60
- bendAllowance: 1.8
- kFactor: 0.35
Result: Bend allowance = 2.80 mm
Short bends still need accurate layout if you are making several pieces. The estimate is 2.80 mm.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| K under 0.30 | Neutral axis close to the inside surface | Check whether the material or tooling is driving a tighter bend. |
| K 0.30 to 0.40 | Common shop range | Often a good starting point for many sheet metal jobs. |
| K 0.40 to 0.50 | Neutral axis farther from the inside | Compare against your machine and material data. |
| Above 0.50 | Unusual bend behavior | Recheck the inputs or use a material-specific bend table. |
Frequently Asked Questions
It estimates the main planning quantity for k-factor work using the formula shown on the page. That gives you a practical number before you order materials, compare suppliers, or talk to a contractor. The K-factor tells you how much of the bend sits outside the neutral axis and helps you lay out sheet metal accurately.
Enter the values that match the unit labels beside the fields. If the page expects feet, inches, gallons, pounds, or watts, keep everything in that unit family so the result stays reliable.
The calculator multiplies or divides the main quantity by the values you enter, so every measurement feeds directly into the final answer. A small change in depth, area, density, or factor can make a large difference on a bigger project.
Yes, as long as the units stay consistent within the calculation. If the page expects feet, inches, gallons, or pounds, convert first so the final result is accurate and easy to interpret.
Treat the result as a planning estimate. Use the main output for sizing or ordering, then review the detail rows for waste, weight, cost, or conversion notes before you finalize the purchase.
Yes if the job involves cut losses, uneven ground, spill risk, or irregular shapes. A small allowance is usually safer than ordering exactly to the bare math, especially for k-factor projects that are hard to top up later.
It is exact for the numbers you enter, but real-world projects can still vary because of compaction, tolerances, site conditions, and product differences. Use the result as a solid working estimate, not a final structural or procurement check.
Yes. That is one of its main uses. The result helps you estimate how much to buy, what it may weigh, and what the budget might look like before you place an order or request a quote.
Disclaimer: This K-factor calculator provides a planning estimate only. Actual bend behavior depends on tooling, grain direction, material grade, and the press brake setup.
Sources
Last reviewed: March 2026