Find a size chart for electric cables at websites such as Powerstream.com and Rapidtables.com. The first website lists a chart on the "Technical Resources" page, under the "Other Power Electronics Resources" heading. Rapidtables.com has a wire gauge chart under the "Wire Calculators" link of the main page; click this link, then click "Wire Gauge Calculator." This webpage features a calculator that allows for input of wire gauge and material type, in addition to an electrical cable size chart.
The charts on Powerstream.com and Rapidtables.com follow the American Wire Gauge standard for electric cables, measuring size by the gauge of a wire. The diameter of a wire is equal to 0.005 multiplied by 92, the second number which is raised to the power of 36 minus the gauge of a wire divided by 39.
The gauge of an electrical wire ranges from numerical designations of "0000" to 40; generally, the relationship is that a higher gauge numbers has smaller wire diameters. Thus, 40-gauge wire is 0.0031 inches thick, while "0000" gauge wire has a 0.46 inch diameter. Generally, thicker gauges of wire have a higher maximum amperage tolerance, a higher breaking force and a lower resistance to electrical current than thinner wire diameters.