Aluminum sheet is still bought by gauge number across North America, and the gauge chart is where most ordering mistakes start — because aluminum gauge is not steel gauge. This page is the aluminum gauge to mm chart on the Brown & Sharpe (B&S) scale, the one the Aluminum Association uses, with the millimeter value and the tolerance band for each gauge.
The single most important thing to remember: a lower gauge number means thicker metal. 8 gauge is thick, 28 gauge is thin. And because aluminum uses the B&S scale while steel uses the Manufacturers' Standard Gauge, a "16 gauge" aluminum sheet is a different physical thickness from a "16 gauge" steel sheet.
Aluminum gauge to mm chart (B&S)
| Gauge | Decimal inches | Millimeters | Typical tolerance (ASTM B209) |
|---|---|---|---|
| 8 ga | 0.1285" | 3.26 mm | 3.13 – 3.39 mm |
| 10 ga | 0.1019" | 2.59 mm | 2.46 – 2.72 mm |
| 12 ga | 0.0808" | 2.05 mm | 1.95 – 2.15 mm |
| 14 ga | 0.0641" | 1.63 mm | 1.55 – 1.71 mm |
| 16 ga | 0.0508" | 1.29 mm | 1.21 – 1.37 mm |
| 18 ga | 0.0403" | 1.02 mm | 0.94 – 1.10 mm |
| 20 ga | 0.0320" | 0.81 mm | 0.76 – 0.86 mm |
| 22 ga | 0.0253" | 0.64 mm | 0.59 – 0.69 mm |
| 24 ga | 0.0201" | 0.51 mm | 0.47 – 0.55 mm |
| 26 ga | 0.0159" | 0.40 mm | 0.36 – 0.44 mm |
| 28 ga | 0.0126" | 0.32 mm | 0.28 – 0.36 mm |
The millimeter values are the B&S nominal conversions. The tolerance band is the ASTM B209 range for each gauge — notice that the band is not symmetric in absolute millimeters at the thin end, which is why a supplier quotes a range rather than a single ± figure for very thin sheet.
Why gauge is a trap
Three things trip buyers up, and they are all avoidable:
- Aluminum gauge ≠ steel gauge. A 16 ga aluminum sheet is 1.29 mm; a 16 ga steel sheet is about 1.52 mm. If you spec "16 gauge" and the supplier assumes steel, you get the wrong metal and the wrong thickness.
- Gauge is not a universal standard. It is a North American convention. Most of the world specifies sheet in millimeters. On an international order, millimeters are unambiguous — gauge is not.
- Gauge maps to nominal thickness, not exact thickness. A 16 ga sheet is 1.29 mm nominal, but the actual material sits inside a tolerance band around that. For work that depends on a precise thickness, specify the millimeter and the tolerance, not the gauge.
The professional habit is to specify in decimal or millimeters, and use gauge only as a shorthand in conversation. If a drawing has to be checked, "0.040 inch" or "1.02 mm" leaves no room for the steel-versus-aluminum confusion.
Sheet versus plate
There is a dividing line worth knowing: roughly 6 mm (0.250 inch) is where sheet becomes plate. Below it, the material is sheet, rolled and cut to length; above it, plate, with different tolerances, handling and often different pricing. If you order "heavy gauge" stock and a supplier quotes plate pricing, this is why.
The gauge chart above stops at 8 ga (3.26 mm) because that is where the B&S sheet scale runs out; beyond it you are in plate territory and should specify thickness in millimeters directly.
Weight by gauge
Because weight drives freight and pricing, here is the weight per square metre at the nominal gauge, using the 2.70 g/cm³ density that is the standard planning figure:
| Gauge | Thickness (mm) | Weight (kg/m²) |
|---|---|---|
| 10 ga | 2.59 | 7.0 |
| 12 ga | 2.05 | 5.5 |
| 14 ga | 1.63 | 4.4 |
| 16 ga | 1.29 | 3.5 |
| 18 ga | 1.02 | 2.8 |
| 20 ga | 0.81 | 2.2 |
| 22 ga | 0.64 | 1.7 |
| 24 ga | 0.51 | 1.4 |
The formula is simple: weight per square metre (kg) = thickness in mm × density in g/cm³. A 2 mm sheet weighs 2 × 2.70 = 5.4 kg/m². This is the same arithmetic the weight calculator uses, and it is exact per alloy once you use the alloy's own density rather than the 2.70 planning figure.
The rule that prevents mistakes
Never order sheet by gauge across a metric boundary. If your shop works in millimeters, order in millimeters. If the supplier or drawing uses gauge, convert it yourself with the chart above and write the millimeter value on the order. That one step removes the steel-versus-aluminum, metric-versus-imperial, and nominal-versus-actual confusions in a single move.
For the alloy and temper that go with a given thickness, see the grade reference pages. If you are not sure which gauge a part actually needs, send the drawing — the thickness is usually decided by the span and the forming, not by habit.