Knowing the thickness of your wire is very important in chain maille, and you need to be sure you understand its importance when it comes time to buy your own wire or rings. The thickness of wire is usually measured using a wire gauge system, which assigns a given number (e.g. 14 gauge) a specific diameter (e.g. .080″), typically measured to the thousandths of an inch or in millimeters.
As if three different ways of stating the thickness of wire isn’t enough (in, mm, gauge #) there are two different wire gauge systems, the American Wire Gauge (AWG), also known as the Brown & Sharpe wire gauge, and the Standard Wire Gauge (SWG). A general rule for both of these wire gauge systems is that the larger the gauge number, the smaller the wire diameter, and vice versa. Despite this similarity, a given gauge number in AWG does not match the same diameter as the same gauge number in SWG. Its important when communicating to others about wire thickness or purchasing wire and rings to note the gauge system that the thickness is listed in, to avoid confusion to others and to ensure that you are buying the right wire. The best way to avoid confusion is to look for, or state when communicating to another, the diameter of the wire in an actual measurement system. Either the imperial system, in thousandths of an inch (e.g. .080″), or in the metric system, in millimeters (e.g. 2.0 mm). Whichever you prefer, either one is much less confusing than one of the gauge systems. As a rule of thumb, always measure the inner diameter of the ring, or the ring size, in the same system as you measure the gauge. This is important when considering Aspect Ratio, which is the ratio of the inner diameter of the ring to the wire size.
Below is a picture of the most commonly used wire gauges, from thinnest to largest. each is labeled with the gauge number for both AWG and SWG, as well as the actual measurement in inches and millimeters. The smaller gauges, or thicker wires, are generally used for armor, while the larger gauges, or thinner wires, are generally used for jewelry. Gauges outside this range can, and have been used, but they typically lose practicality so are rarely used.
Be careful when dealing with wire thickness to be careful when purchasing, and clear when communicating with others. See my post on Aspect Ratio to understand the importance of choosing the correct wire gauge and inner diameter for a ring.