Metal Gauge Chart
Gauges (ga) shown here are American Wire Gauge (AWG), also known as Brown & Sharpe (B&S), along with the corresponding diameters in millimeters (mm) and inches (in).
|American Wire Gauge (AWG) Gauge (ga)||Millimeters (mm)||Inches (in)|
Metal Gauge to measurement has a logarithmic relationship, unlike with the Leather Thickness oz to mm chart, which shows a linear relationship. This logarithmic relationship makes conversions a bit difficult on the fly, so use of a tool to measure the thickness or diameters (e.g. calipers) or the gauge (e.g. wire gauge; yep, the tool and [one of] the thing[s] it measures are called by the same name), and then referencing the chart to see your other desired value.
example: I have unmarked silver wire sitting around and I need to know if I can use it in a project which calls for 19 ga wire. Using calipers to measure wire's diameter, I find it's 0.91 mm. Checking the chart for the mm measurement, then scanning left to the AWG Gauge value, and I see that I have 19 ga wire and am good to go.
Gauge apply to both wire diameter and sheet thickness.
Gauges are one of those "reverse" things, where the higher the gauge number is, the smaller the diameter of the wire or thickness of the sheet. This came about because the people who drew the wire based the gauge value on the number of draws it took to reduce the diameter of the wire to the desired thickness -- smaller diameters required more draws, thus a higher number -- and then sheet metal makers decided to use the same measurement-to-gauge values.1https://www.wileymetal.com/why-is-sheet-metal-thickness-measured-in-gauge-and-not-inches/
American Wire Gauge (AWG), also known as Brown & Sharpe (B&S), applies to non-ferrous metals and because a jeweler or metalsmith is typically (not always, of course) working with the non-ferrous base and precious metals, we're using the AWS standard here.
There are other gauge systems out there, such as the Standard Wire Gauge (SWG) (a.k.a. British Standard Gauge and Imperial Wire Gauge), and American Manufacturers Standard Gauge (MSG) for steel (regular, galvanized, and stainless). It's important to use the correct gauge standard for the given metal you're working with because the gauge to measurement correlations do differ.
When purchasing your metal wire or sheet, it is important to know which gauge standard the Vendor is using, as that might differ from what you're used to using. If they provide gauge without reference which standard, look for another measurement (mm or in) then use the AWG chart to convert that measurement to gauge to know if it's the gauge you need.