Wire gauge

Figure 1. A diagram showing the different gauges of wire and their corresponding number based on its cross section.

Wire gauge is the measure of how large of a cross section a wire has. Knowing the gauge is important because it tells you how much current a wire can carry without being damaged - this quantity is called ampacity.

American Wire Gauge System

The American Wire Gauge system or AWG allows for standard wire sizes - determined by cross sectional area - to be identified and assigns them an AWG number. A lower gauge wire has a larger diameter and thus is able to carry higher currents. There are a total of 40 different gauge sizes with cross sectional areas ranging from 0.013 mm² to 107.22 mm² with their diameters changing incrementally between each gauge number.

Wire Gauge Values

AWG number	Cross sectional area (mm2)	Ohms/km (/km)	Ampacity (A)	Usage example
18	0.82	20.95	14	Low voltage lighting
16	1.31	13.18	18	Extension cords
14	2.08	8.28	25	Lighting fixtures
12	3.31	5.21	30	Kitchen appliances
10	5.26	3.28	40	Electric dryers
8	8.37	2.06	55	Electric ovens
6	13.30	1.30	75	Large electric heaters
4	21.15	0.81	85	Large furnaces
3	26.67	0.65	115	Large commercial wiring
2	33.63	0.51	130	Car battery cable
1	42.41	0.41	145	Power distribution
1/0	53.47	0.32	170	Power distribution
2/0	67.43	0.26	195	Power distribution
3/0	85.03	0.20	225	Power distribution
4/0	107.22	0.16	260	Power distribution
250	126.68	0.13	290	Power distribution
350	177.35	0.10	350	Power distribution
400	202.68	0.08	380	Power distribution

The figures above are taken from Table 310.15(B)(16) in the 2014 National Electrical Code (USA) and assume a temperature rating of 90°C. Also, Table 3.1 on page 69 in Introduction to Electricity was used as a template and reference.

For a more complete list, please see Dr. Rowlett's unit page.