Sheet Metal Bend Allowance Calculator
Free Sheet metal bend allowance Calculator for materials specifications projects. Enter dimensions to get material lists and cost estimates.
Formula
BA = (Angle in radians) x (Inside Radius + K-factor x Thickness)
Bend allowance equals the bend angle converted to radians multiplied by the neutral axis radius. The neutral axis radius is the inside bend radius plus the K-factor times the material thickness. Bend deduction is calculated as: BD = 2 x OSSB - BA, where OSSB (outside setback) = (R + T) x tan(Angle/2).
Frequently Asked Questions
What is bend allowance in sheet metal?
Bend allowance is the arc length of the neutral axis through the bend zone. It represents the amount of material consumed by the bend and must be added to the flat flange dimensions to calculate the total flat pattern (blank) length. Without accurate bend allowance, the finished part will be either too long or too short. The formula is BA = (Bend Angle in radians) x (Inside Radius + K-factor x Thickness).
What is the difference between bend allowance and bend deduction?
Bend allowance (BA) is the arc length of the neutral axis and gets added to flat dimensions to calculate blank size. Bend deduction (BD) is subtracted from the sum of the outside flange dimensions. They are related by: BD = 2 x Outside Setback - BA. Both methods produce the same flat pattern length when applied correctly. CAD systems typically use bend allowance internally, while shop floor personnel often prefer bend deduction for manual calculations.
How does the K-factor affect bend allowance?
The K-factor determines where the neutral axis sits within the material thickness during bending. A higher K-factor (closer to 0.50) places the neutral axis near the center, producing a larger bend allowance. A lower K-factor (closer to 0.33) places it toward the inside of the bend, giving a smaller bend allowance. For standard air bending of mild steel, 0.40-0.45 is typical. The K-factor depends on material type, bend radius to thickness ratio, and bending method.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
Can I use Sheet Metal Bend Allowance Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.