Gauge, often abbreviated to SWG, is a unit of measurement used industry-wide to measure the thickness of sheet metal. Unlike most units of measurement, with SWG, the higher the number, the greater the thickness of the material. For example, in the case of galvanised steel sheet, 5 SWG is 5mm thick, whilst 24 SWG is 0.5mm thick. Read on to find out more about sheet metal gauge and how it is measured.
Can all metals be measured using the same SWG chart?
No. It’s important to note that SWG measurements vary between metals, so a 14 SWG sheet of Corten steel is 2.5mm thick, whilst a 14 SWG sheet of aluminium is 2mm thick. Confused? Don’t panic – to make ordering your metal much easier for you, we use a conversion key on our website, so that you can see the equivalent thickness in millimetres right next to our products’ SWGs. We do love to geek out on all things metal, though, so if you’d still like to know a little bit more about the gauge measurement and its history, read on.
What does SWG stand for?
SWG stands for Standard Wire Gauge, a name taken from British Standard Wire Gauge. There is also an American Wire Gauge, which is similar to SWG but not exactly the same. As we’re in the UK, this article refers to the British SWG.
A steel wire gauge tool used to measure the diameter of wire.
What’s the history of the gauge?
The original SWG was made the legal standard by the British Board of Trade in 1884, as an improvement on the already-existing Birmingham Wire Gauge. As the name suggests, the gauge was originally developed to measure the diameter of wire. When it comes to wire, SWG is often measured using a tool, also called a wire gauge. The wire gauge has lots of circular holes on it, which wire can be threaded through to determine its diameter (or SWG). These days, most electrical cables are measured in square millimetres of cross-sectional area, but SWG is still used for some types of wires and for sheet metal.
How do I measure the gauge of sheet metal?
You can purchase a tool, similar to the wire gauge one we mentioned earlier, to measure sheet metal. It’s similar in design to the wire gauge, but instead of the circles, features rectangular notches that you can slot pieces of sheet metal into to determine their thickness and gauge. The simplest way to find out what gauge a piece of sheet metal is, though, is to simply measure it using a tape measure or ruler, then compare it to a conversion chart like the one for galvanised steel below.
SWG conversion chart for galvanised steel
Measurements in mm
Measurements in inches
The above table shows the UK SWG conversion rates for galvanised steel, to the nearest decimal point in millimetres, and also in inches. As you can see, the higher the SWG, the lower the measurement in millimetres or inches. Remember that not all metals have the same gauge conversion rates; that’s why we include conversions to both millimetres and inches on our metals to make selecting the right thickness of metal easy for you.