Reference
Sheet Metal Gauge & Bend Radius Chart
Gauge-to-thickness conversion, minimum inside bend radius by material, and typical K-factors, for designing sheet-metal parts that form cleanly.
Most sheet-metal design limits come from the material thickness and the bend. This chart converts gauge to thickness, gives the minimum inside bend radius you can form without cracking, and lists the K-factors that set your flat-pattern length. Rule of thumb: keep the inside bend radius at least equal to the material thickness.
Sheet metal gauge to thickness
Steel uses the Manufacturers' Standard Gauge; aluminum uses its own (thinner) gauge. Always confirm thickness, not gauge, on your drawing.
| Gauge | Steel (in) | Steel (mm) | Aluminum (in) |
|---|---|---|---|
| 10 | 0.1345 | 3.42 | 0.1019 |
| 11 | 0.1196 | 3.04 | 0.0907 |
| 12 | 0.1046 | 2.66 | 0.0808 |
| 14 | 0.0747 | 1.90 | 0.0641 |
| 16 | 0.0598 | 1.52 | 0.0508 |
| 18 | 0.0478 | 1.21 | 0.0403 |
| 20 | 0.0359 | 0.91 | 0.0320 |
| 22 | 0.0299 | 0.76 | 0.0253 |
| 24 | 0.0239 | 0.61 | 0.0201 |
Representative values; sheet stock varies slightly by mill and spec.
Minimum inside bend radius by material
Tighter radii than these tend to crack the outside of the bend or need special tooling. Softer tempers bend tighter than hard ones.
| Material | Min inside bend radius |
|---|---|
| Aluminum 5052 | ~0.5 to 1x thickness |
| Aluminum 6061-T6 | ~1 to 2x thickness (cracks easily) |
| Cold-rolled steel | ~0.5 to 1x thickness |
| Stainless 304 | ~0.5 to 1x thickness |
| General rule | >= 1x material thickness |
When in doubt, set the inside radius equal to the material thickness.
Typical K-factors
The K-factor is where the neutral axis sits through the bend; it drives how much the flat pattern stretches. Shops tune it to their tooling, but these are common starting points.
| Material condition | Typical K-factor |
|---|---|
| Soft (aluminum, annealed) | 0.33 |
| Medium (cold-rolled steel) | 0.40 to 0.45 |
| Hard (stainless, spring temper) | 0.45 to 0.50 |
Values reflect common sheet-metal practice. A shop confirms bend radius and flat pattern against its own tooling and your material.