Sheet Metal Gauge to mm: UK Thickness Chart & Converter
Sheet metal gauge is a measure of thickness — and the higher the gauge number, the thinner the metal. The catch is that a gauge does not convert to the same thickness for every metal: 16 gauge is about 1.52mm in mild steel, 1.61mm in galvanised steel, 1.59mm in stainless steel, and 1.29mm in aluminium. This guide gives you a free gauge-to-mm converter, the full UK thickness chart for each metal, and plain-English advice on which to order in.
What is sheet metal gauge?
Gauge (sometimes written “ga” or “g”) is a traditional, non-metric way of describing sheet metal thickness. It dates back to the wire-drawing industry, where thickness was defined by how many times the metal had been passed through the drawing dies — so a higher number meant more passes and a thinner result. That is why the numbering feels backwards: a lower gauge number is a thicker sheet, and a higher gauge number is a thinner sheet. 10 gauge steel (about 3.4mm) is much thicker than 20 gauge steel (about 0.9mm).
Because the gauge systems were set separately for different metals, the same gauge number lands on a different thickness depending on whether you are buying steel, galvanised steel, stainless steel or aluminium. Always check the material as well as the number.
Sheet metal gauge to mm converter
Pick your metal and gauge to get the thickness in millimetres — or enter a thickness in mm to find the nearest gauge.
Gauge ↔ mm converter
Values are nominal industry-standard thicknesses and vary slightly by supplier and standard. In the UK, sheet is sold by mm — use these to translate a gauge spec into the millimetre size to order.
Browse metal sheet & plateSheet metal gauge to mm chart (UK)
The full conversion for the four metals we supply. Thicknesses are the nominal industry standards in millimetres.
| Gauge | Mild steel (mm) | Galvanised (mm) | Stainless (mm) | Aluminium (mm) |
|---|---|---|---|---|
| 7 | 4.55 | – | 4.76 | – |
| 8 | 4.18 | 4.27 | 4.37 | 3.26 |
| 10 | 3.42 | 3.51 | 3.57 | 2.59 |
| 11 | 3.04 | 3.13 | 3.18 | – |
| 12 | 2.66 | 2.75 | 2.78 | 2.05 |
| 14 | 1.90 | 1.99 | 1.98 | 1.63 |
| 16 | 1.52 | 1.61 | 1.59 | 1.29 |
| 18 | 1.21 | 1.31 | 1.27 | 1.02 |
| 20 | 0.91 | 1.01 | 0.95 | 0.81 |
| 22 | 0.76 | 0.85 | 0.79 | 0.64 |
| 24 | 0.61 | 0.70 | 0.64 | – |
| 26 | 0.45 | 0.55 | 0.48 | – |
Why does a higher gauge mean a thinner sheet?
It is a hangover from how sheet and wire were originally made. Metal was drawn thinner with each pass through a die, and the gauge number recorded the number of passes — so more passes (a higher number) produced a thinner product. The system stuck even though we now roll sheet to a target thickness directly. The practical takeaway: if someone asks for “a thicker gauge”, they usually mean a lower gauge number. When in doubt, talk in millimetres.
Why gauge is different for each metal
There isn’t one universal gauge system. Steel sheet typically follows the Manufacturers’ Standard Gauge; galvanised steel adds the zinc coating, so each gauge is fractionally thicker than plain steel; stainless steel uses its own gauge standard; and aluminium follows the Brown & Sharpe (American Wire Gauge) system, which is thinner again for the same number. That is why 16 gauge ranges from about 1.29mm in aluminium up to 1.61mm in galvanised steel. Match the gauge to the metal, or you can be out by 20–30%.
Should you order in gauge or mm?
In the UK, sheet metal is sold by millimetre thickness, not gauge. Gauge is still useful for reading older drawings, imported specs and American guides, but when you place an order, convert to mm first and quote the mm thickness. It removes any ambiguity about which gauge system a supplier is using. Use the converter above to get your mm figure, then order that thickness.
Common sheet metal thicknesses and what they’re used for
- 0.7–0.9mm (about 20–22 ga) – light fabrication, trims, ductwork, panels.
- 1.2mm (about 18 ga) – general sheet-metal work, enclosures, brackets, splashbacks.
- 1.5–2mm (about 14–16 ga) – the workhorse range for gates, covers, heavier brackets and repairs.
- 3mm (about 10–11 ga) – structural brackets, base plates, wear surfaces, ramps.
- 4mm and up – into plate territory for load-bearing and heavy-duty work.
Buy sheet metal at Rackerman
Rackerman supplies mild steel sheet and metal plate, galvanised steel sheet, stainless steel sheet and aluminium sheet — all in standard UK millimetre thicknesses and full sheet sizes (8x4, 2m x 1m and more). Not sure which grade or finish you need? Our guides on galvanised steel and steel vs aluminium explain the differences.
Browse metal sheet & plate at Rackerman →
Frequently asked questions
What is 16 gauge in mm? About 1.52mm in mild steel, 1.61mm in galvanised steel, 1.59mm in stainless steel and 1.29mm in aluminium. Gauge converts differently for each metal, so always check the material.
Is a higher gauge thicker or thinner? Thinner. A higher gauge number means a thinner sheet — 20 gauge is thinner than 10 gauge. It’s the reverse of what most people expect.
What gauge is 2mm steel? Roughly 14 gauge in mild steel (14 ga is about 1.90mm). For an exact 2mm, order 2mm by millimetre rather than by gauge.
What gauge is 1mm steel? About 19–20 gauge in mild steel (20 ga is around 0.91mm). Again, ordering 1mm by mm is more precise.
Why is aluminium a different thickness for the same gauge? Aluminium uses the Brown & Sharpe (AWG) gauge system, which is thinner than the steel Manufacturers’ Standard Gauge, so 16 gauge aluminium (about 1.29mm) is thinner than 16 gauge steel (about 1.52mm).
Does galvanised steel measure thicker than plain steel at the same gauge? Slightly, yes — the zinc coating adds a little thickness, so each galvanised gauge is fractionally thicker than the uncoated steel equivalent.
Should I order sheet metal in gauge or mm? In the UK, order in millimetres. Sheet is sold by mm, and quoting mm removes any confusion about which gauge system applies. Convert your gauge to mm first.
What’s the thickest sheet before it becomes plate? There’s no hard line, but metal up to about 3mm is generally called sheet, and above that it’s usually referred to as plate.