Sheet Metal Flat Pattern Length Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Sheet Metal Flat Pattern Length Calculator
Laying out a multi-bend sheet metal part requires summing flange lengths plus each bend's contribution to total material length - this calculator handles the full calculation.
Formula
Bend Allowance Per Bend = (π/180) × Angle × (Radius + K × Thickness)
Flat Pattern Length = Sum of Flange Lengths + (Bend Allowance × Number of Bends)
Example
Two 50mm flanges, 2mm material thickness, 3mm bend radius, 1 bend at 90┬░:
Bend Allowance = 6.095mm → Flat Pattern Length = 106.09mm
The K-Factor
This calculation uses a K-factor of 0.44, a commonly used default representing where the neutral bending axis sits within the material thickness (as a fraction from the inside surface) - the true K-factor varies somewhat by specific material, thickness, and bending method, so precision fabrication shops often determine their own empirical K-factor through test bends on their specific equipment.
Measuring Flange Lengths Correctly
Flange lengths must be measured to each bend's apex (the theoretical sharp corner point, not the actual rounded bend surface) for this formula to produce an accurate total - this is a standard sheet metal drafting convention that keeps the math consistent regardless of the actual bend radius used.