Sheet metal gauge chart: gauge to mm and inches.
16 gauge mild steel is 1.519 mm. 16 gauge aluminium is 1.290 mm. 16 gauge galvanized is 1.613 mm. Same number, three thicknesses — which is exactly why every fab shop needs one reliable gauge-to-mm chart and why your drawings should say millimetres, not gauge.
What sheet metal gauge actually means
Gauge numbers date back to wire drawing: the number roughly counted how many times the stock passed through a die, so a higher gauge means a thinner sheet. For steel, the Manufacturers' Standard Gage (MSG) was later defined from weight — a gauge number corresponds to a nominal weight in ounces per square foot, converted to thickness using 41.82 lb/ft² per inch. That history is why the numbers look arbitrary and why they never quite line up between materials.
Three different systems survive in daily use: MSG for carbon and mild steel, MSG plus a coating allowance for galvanized steel (roughly +0.09 mm for the zinc), and AWG / Brown & Sharpe for aluminium, brass and copper. Stainless steel uses its own chart close to, but not identical with, mild steel.
Gauge to mm conversion chart
Thicknesses below are the commonly published nominal values. Suppliers work to a thickness tolerance around these (see steel weight calculation for how nominal vs actual thickness moves your material cost).
| Gauge | Mild steel mm (in) | Galvanized mm | Stainless mm | Aluminium mm |
|---|---|---|---|---|
| 7 | 4.554 (0.1793) | — | 4.763 | 3.665 |
| 8 | 4.176 (0.1644) | 4.270 | 4.366 | 3.264 |
| 10 | 3.416 (0.1345) | 3.510 | 3.571 | 2.588 |
| 11 | 3.038 (0.1196) | 3.132 | 3.175 | 2.305 |
| 12 | 2.657 (0.1046) | 2.753 | 2.778 | 2.053 |
| 14 | 1.897 (0.0747) | 1.994 | 1.984 | 1.628 |
| 16 | 1.519 (0.0598) | 1.613 | 1.588 | 1.290 |
| 18 | 1.214 (0.0478) | 1.311 | 1.270 | 1.024 |
| 20 | 0.912 (0.0359) | 1.006 | 0.953 | 0.813 |
| 22 | 0.759 (0.0299) | 0.853 | 0.794 | 0.643 |
| 24 | 0.607 (0.0239) | 0.701 | 0.635 | 0.511 |
| 26 | 0.455 (0.0179) | 0.551 | 0.478 | 0.404 |
Weight per square metre (steel)
Weight follows directly from thickness: kg/m² = thickness in mm × 7.85 for steel. Useful when converting a coil weight into blanks, or sanity-checking a supplier invoice.
| Gauge | Thickness (mm) | Steel weight (kg/m²) |
|---|---|---|
| 10 | 3.416 | 26.8 |
| 12 | 2.657 | 20.9 |
| 14 | 1.897 | 14.9 |
| 16 | 1.519 | 11.9 |
| 18 | 1.214 | 9.5 |
| 20 | 0.912 | 7.2 |
| 22 | 0.759 | 6.0 |
| 24 | 0.607 | 4.8 |
For other materials and full-sheet weights, the material weight calculator handles plate, sheet, bar and pipe with the right densities.
Why the same gauge differs by material
Because the systems were never connected. MSG for steel is weight-based (41.82 lb/ft²/in). AWG for aluminium is a geometric wire series where each step is a constant ratio in area. Galvanized adds a zinc allowance on top of MSG. So a purchase order that just says “16 gauge sheet” without the material system is genuinely ambiguous by more than 0.3 mm — enough to change bend results, weld settings and part weight.
Thickness also drives your press-brake numbers directly: bend allowance, K-factor and minimum bend radius all scale with it. If you pull a thickness from this chart for a flat-pattern calculation, run it through the bend allowance calculator rather than assuming the neutral axis sits mid-thickness — the companion guide on bend allowance and K-factor shows why that assumption fails on tight radii.
What to write on drawings instead
In 14 years running plants I have rejected exactly zero sheets for being “not 16 gauge” — and several lots for being outside a millimetre tolerance. Gauge is a trade name, not a dimension. On drawings and POs:
- State thickness in mm with a tolerance — e.g. 1.50 ±0.09 mm, aligned to the mill standard (ASTM A480 for stainless, IS 513 / IS 1852 for Indian CR/HR sheet, EN 10143 for coated steel).
- Name the material and condition — CRCA IS 513 Gr D, SS304 2B, Al 5052-H32 — so incoming inspection has something enforceable.
- Add gauge in brackets only as reference, if your buyers and vendors still speak gauge: “1.5 mm (16 ga) CRCA”.
- Measure at incoming with a flat-anvil micrometer away from sheared edges, and record it — thin-side material quietly erodes weld quality and blank weight.
Common mistakes
- Mixing gauge systems across materials. A jig set for 16 ga steel will not suit 16 ga aluminium — 0.23 mm difference shows up immediately in bends and welds.
- Quoting weight from gauge nominals without checking the mill's actual thickness tolerance band — on a 10-tonne order the difference is real money.
- Reusing K-factors across thicknesses. A K-factor proven on 1.2 mm does not transfer to 3 mm on the same tooling.
- Letting POs say only “gauge”. Disputes at incoming inspection are unwinnable without a mm tolerance on paper.
When the parts move to fabrication and inspection, the drawing's thickness callout is one more characteristic to capture. CadNexa's auto-ballooning tool reads it off the PDF along with every other dimension, so your incoming and first-piece inspection sheets list the real 1.50 ±0.09 mm requirement — not a gauge number nobody can measure. Free report formats are also on the templates page.