Sheet metal

Flat Pattern Length Calculator

Estimate a two-flange, single-bend flat blank from outside flange lengths. This tool calculates bend allowance and bend deduction from the angle, inside radius, thickness, and K-factor entered in the same form.

mild steel16 ga0.0598 in1.519 mm

Interactive calculator

Flat Pattern Length Calculator

Flat pattern length3.8942 in
Bend deduction used0.1058 in

Static reference

Common thickness, radius, and angle combinations

Swipe table horizontally for more columns.

GaugeThicknessInside radiusAngleBend allowanceBend deduction
16 ga0.0598 in / 1.519 mm0.0598 in / 1.519 mm45 deg0.0667 in0.0324 in
12 ga0.1046 in / 2.657 mm0.1569 in / 3.985 mm90 deg0.3155 in0.2075 in

Formula used

What this calculator computes

Flat = A_flange + B_flange − BD
Flat
Developed flat blank length (in or mm)
A_flange
Outside length of flange A (in or mm)
B_flange
Outside length of flange B (in or mm)
BD
Bend deduction calculated from the entered angle, inside radius, thickness, and K-factor (in or mm)
  • The calculator derives BA = (π / 180) × A × (r + K × t), then OSSB = tan(A / 2) × (r + t), and finally BD = 2 × OSSB − BA before subtracting BD from the two outside flanges.
  • Two-flange / single-bend math only. For multi-bend parts, repeat the deduction at every bend and account for bend order, tooling clearance, and accumulated tolerance.

Worked example

One numeric walk-through

Inputs

Flange A
2.000 in
Flange B
2.000 in
Thickness t
0.0598 in
Inside radius r
0.0598 in
Bend angle A
90°
K-factor
0.42

Steps

  1. BA = (π / 180) × 90 × (0.0598 + 0.42 × 0.0598) ≈ 0.1334 in.
  2. OSSB = tan(45°) × (0.0598 + 0.0598) = 0.1196 in.
  3. BD = 2 × 0.1196 − 0.1334 ≈ 0.1058 in.
  4. Flat = 2.000 + 2.000 − 0.1058 = 3.8942 in.

Result

Flat blank length ≈ 3.894 in for the two outside flanges entered.

Common mistakes

Things to check before trusting the number

Related calculators

Move between connected shop calculations

K-factorBend allowanceBend deductionFlat patternMinimum bend radiusReverse K-factorPress brake tonnageData sources

FAQ

Specific checks for this calculator

Are the flange lengths inside or outside dimensions?

Outside flange dimensions. Subtract bend deduction from their sum to get the flat blank.

Can I use this for multi-bend parts?

Apply the same principle bend-by-bend, but multi-bend parts also need bend order, tooling clearance, and accumulated tolerance — handle those externally.