A Guide to Sheet Metal Gauges and Conversions 

Sheet metal, metal which has been processed into thin, flat pieces, is one of the most common forms available due to its versatility and ease of transport and storage. Extremely thin sheet metals are more commonly known as foils, and thicker sheets of metal are often referred to as plates. Sheet metal can be found throughout history used for walls, roofs, containers, and even suits of armour! Sheet metals these days have almost unlimited applications across the construction, manufacturing, automobile, aerospace and marine industries, as well as for protection or decoration.

What Are Sheet Metal Gauges?

Sheet metal thickness is often specified by a measurement system known as the gauge system. Gauge numbers (sometimes abbreviated in certain parts of the world as Ga.) are non-linear and are based around measurements made in fractions of inches, so converting them to millimetres is not a simple or consistent calculation. The actual gauge numbers seem almost arbitrary, and to understand the thickness that is being specified in either metric or imperial measurements requires the use of a gauge conversion chart.

It is important to note that as sheet metal is formed, the rolling process can cause some deviation in thickness. The variation in thickness that is allowed within each gauge is known as tolerance. Because of these discrepancies and because of the different gauge systems found around the world, it is highly advisable to specify your sheet metal requirements in millimetres or inches.

The Standard Wire Gauge (SWG), also known as the British Standard Gauge, is the most commonly used in the United Kingdom, and the Manufacturer’s Standard Gauge (MSG) in the USA. The system is used to denote the thickness of sheet metal as well as wire.

Different metals use different gauge systems, so when using certain systems, 20 gauge steel will not have the same thickness as 20 gauge aluminium. This is because different measurements are used for ferrous (which contain iron) and non-ferrous metals (such as aluminium, brass, and copper).

Standard Wire Gauge Conversion Chart 

1 SWG = 0.300” / 7.620 mm

16 SWG = 0.064” / 1.626 mm

2 SWG = 0.276” / 7.010 mm

17 SWG = 0.056” / 1.422 mm

3 SWG = 0.252” / 6.401 mm

18 SWG = 0.048” / 1.219 mm

4 SWG = 0.232” / 5.893 mm

19 SWG = 0.040” / 1.016 mm

5 SWG = 0.212” / 5.385 mm

20 SWG = 0.036” / 0.914 mm

6 SWG = 0.192” / 4.877 mm

21 SWG = 0.032” / 0.813 mm

7 SWG = 0.176” / 4.470 mm

22 SWG = 0.028” / 0.711 mm

8 SWG = 0.160” / 4.064 mm

23 SWG = 0.024” / 0.610 mm

9 SWG = 0.144” / 3.658 mm

24 SWG = 0.022” / 0.559 mm

10 SWG = 0.128” / 3.251 mm

25 SWG = 0.020” / 0.508 mm


It is worth noting that thicker sheets than specified on this chart are available, but will be referred to simply by their measurements rather than a gauge number.

There is a range of tools available to measure the thickness of sheet metal. Traditionally the calliper is the most popular option, though now a digital calliper is far easier to read and more accurate. It is also possible to use an ultrasonic thickness meter, useful in certain scenarios where you may not have easy access to the sheet’s edges, and there are specialist gauge tools available with labelled holes or slots to identify different gauges.


We stock a full range of sheet metal in a wide choice of thicknesses and available in aluminium, brass, copper, mild steel, and stainless-steel.