Compute bend allowance, bend deduction, and flat length fast. Build cleaner sheet metal layouts using practical construction inputs today.
| Case | Thickness | Inside Radius | Angle | K-Factor | Single BA |
|---|---|---|---|---|---|
| Light flashing | 1.20 mm | 1.50 mm | 90° | 0.33 | 2.8579 mm |
| General trim | 2.00 mm | 3.00 mm | 90° | 0.33 | 5.1787 mm |
| Heavy cover | 3.00 mm | 4.50 mm | 120° | 0.38 | 11.9381 mm |
Bend Allowance: BA = (π / 180) × A × (R + K × T)
Outside Setback: OSSB = tan(A / 2) × (R + T)
Bend Deduction: BD = 2 × OSSB − BA
Single Flat Length: FL = Leg 1 + Leg 2 − BD
Total Flat Length: Total Outside Straight Length − (BD × Number of Bends)
Where A is bend angle, R is inside radius, T is thickness, and K is the neutral axis factor.
Bend allowance helps fabricators cut accurate flat blanks before bending sheet metal. It matters in flashing, trim work, duct components, brackets, panels, covers, and field-made accessories.
Construction teams often work with galvanized steel, stainless steel, aluminum, and formed plate parts. Small differences in thickness, radius, and K-factor can change flat length enough to affect fit.
This calculator estimates bend allowance, bend deduction, outside setback, and total flat length using standard sheet metal equations. It also adds a simple springback estimate for planning press brake overbend.
Use actual tooling and material test data whenever possible. Shop trials improve K-factor selection. When parts must match existing structures, verify dimensions from the same reference line across all bends.
For multi-bend parts, the best practice is to sum outside straight lengths carefully, then subtract total bend deductions. That method supports layout control and reduces scrap during installation.
Because field conditions vary, this calculator should support planning, pricing, and preliminary fabrication. Final production settings should still follow material standards, tooling data, and your internal quality procedures.
Bend allowance is the arc length of the neutral axis through the bend. It tells you how much material is consumed while the sheet changes direction.
K-factor estimates where the neutral axis sits within the thickness. It strongly affects bend allowance and final flat length accuracy.
Bend deduction is the amount removed from summed outside flange lengths to get the flat pattern. It connects outside dimensions to blank length.
Enter the included bend angle used in your fabrication method. Most shop calculators use the formed angle, such as 90 degrees.
Yes. The equations work for many materials. However, your chosen K-factor and springback assumptions should match the actual material and tooling.
A larger inside radius increases the neutral axis path. That increases bend allowance and can change deduction and developed blank length.
No. It is a planning estimate only. Real springback depends on alloy, grain direction, tooling, tonnage, radius, and process conditions.
Always verify before production runs, tight-fit work, exposed finishes, repeated bends, or whenever the part must match existing field dimensions.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.