Wire Gauge Chart

AWG is an acronym for American Wire Gauge (AWG). AWG sizes may be determined by measuring the diameter of the conductor with the insulation removed (the bare wire). Typically wire is chosen to suit how much amperage it is expected to carry over a certain distance (note that you can always use a thicker wire - lower gauge number - than recommended). As a side note, every 6 gauge decrease gives a doubling of the wire diameter (thickness), and every 3 gauge decrease doubles the wire cross sectional area.

The table below shows various data including both the resistance of the various wire gauges and the allowable current (ampacity) based on plastic insulation. The diameter information in the table applies to solid wires. Stranded wires are calculated by calculating the equivalent cross sectional copper area. The table below assumes DC, or AC frequencies equal to or less than 60 Hz, and does not take skin effect into account. Turns of wire is on a best-case scenario when winding tightly packed coils.

AWG	Diameter		Turns of wire		Area		Copper resistance	Copper resistance^[3]	Copper wire current rating with 60 °C insulation	Approximate stranded metric equivalents
	(inch)	(mm)	(per inch)	(per cm)	(kcmil)	(mm²)	(Ω/1 km)	(Ω/1000 ft)	(A)
000000(6/0)	0.58	14.73	1.72	0.68	336.5	170
00000(5/0)	0.5165	13.12	1.94	0.76	266.8	135
0000(4/0)	0.46	11.68	2.17	0.85	211.6	107	0.16*	0.049*	250
000(3/0)	0.4096	10.4	2.44	0.96	167.8	85	0.2*	0.062*	???
00(2/0)	0.3648	9.266	2.74	1.08	133.1	67.4	0.25*	0.077*
0(1/0)	0.3249	8.251	3.08	1.21	105.5	53.5	~0.3281	~0.1
1	0.2893	7.348	3.46	1.36	83.69	42.4	0.4*	0.12*	110
2	0.2576	6.544	3.88	1.53	66.37	33.6	0.5*	0.15*	95
3	0.2294	5.827	4.36	1.72	52.63	26.7			85	196/0.4
4	0.2043	5.189	4.89	1.93	41.74	21.2	0.8*	0.24*	70
5	0.1819	4.621	5.5	2.17	33.1	16.8				126/0.4
6	0.162	4.115	6.17	2.43	26.25	13.3	1.5*	0.47*	55
7	0.1443	3.665	6.93	2.73	20.72	10.5				80/0.4
8	0.1285	3.264	7.78	3.06	16.52	8.37	2.2*	0.67*	40
9	0.1144	2.906	8.74	3.44	13.08	6.63				>84/0.3
10	0.1019	2.588	9.81	3.86	10.38	5.26	3.2772	0.9989	30	<84/0.3
11	0.0907	2.305	11.03	4.34	8.23	4.17	4.1339	1.26		56/0.3
12	0.0808	2.053	12.38	4.87	6.53	3.31	5.21	1.588	20
13	0.072	1.828	13.89	5.47	5.17	2.62	6.572	2.003		50/0.25
14	0.0641	1.628	15.6	6.14	4.10	2.08	8.284	2.525	15
15	0.0571	1.45	17.51	6.89	3.26	1.65	10.45	3.184		>30/0.25
16	0.0508	1.291	19.69	7.75	2.59	1.31	13.18	4.016	10	<30/0.25
17	0.0453	1.15	22.08	8.69	2.05	1.04	16.614	5.064		32/0.2
18	0.0403	1.02362	24.81	9.77	1.62	0.823	20.948	6.385		>24/0.2
19	0.0359	0.9116	27.86	10.97	1.29	0.653	26.414	8.051		<24/0.2
20	0.032	0.8128	31.25	12.30	1.02	0.518	33.301	10.15		16/0.2
21	0.0285	0.7229	35.09	13.81	0.81	0.41	41.995	12.8
22	0.0253	0.6438	39.53	15.56	0.64	0.326	52.953	16.14		7/0.25
23	0.0226	0.5733	44.25	17.42	0.51	0.258	66.798	20.36
24	0.0201	0.5106	49.75	19.59	0.40	0.205	84.219	25.67		1/0.5, 7/0.2, 30/0.1
25	0.0179	0.4547	55.87	22.00	0.32	0.162	106.201	32.37
26	0.0159	0.4049	62.89	24.76	0.255	0.129	133.891	40.81		7/0.15
27	0.0142	0.3606	70.42	27.72	0.201	0.102	168.865	51.47
28	0.0126	0.3211	79.37	31.25	0.160	0.081	212.927	64.9
29	0.0113	0.2859	88.5	34.84	0.127	0.0642	268.471	81.83
30	0.01	0.2546	100	39.37	0.100	0.0509	338.583	103.2		1/0.25, 7/0.1
31	0.0089	0.2268	112.36	44.24	0.080	0.0404	426.837	130.1
32	0.008	0.2019	125	49.21	0.063	0.032	538.386	164.1		1/0.2, 7/0.08
33	0.0071	0.1798	140.85	55.45	0.050	0.0254	678.806	206.9
34	0.0063	0.1601	158.73	62.49	0.040	0.0201	833	260.9
35	0.0056	0.1426	178.57	70.30	0.032	0.016	1085.958	331
36	0.005	0.127	200	78.74	0.025	0.0127	1360.892	414.8
37	0.0045	0.1131	222.22	87.49	0.020	0.01	1680.118	512.1
38	0.004	0.1007	250	98.43	0.016	0.00797	2127.953	648.6
39	0.0035	0.08969	285.71	112.48	0.012	0.00632	2781.496	847.8
40	0.0031	0.07987	322.58	127.00	0.010	0.00501	3543.307	1080

(*)insulation included

The "Approximate stranded metric equivalents" column lists commonly available cables in the format "number of strands / diameter of individual strand (mm)" which is the common nomenclature describing cable construction within an overall cross-sectional area. Where a common cable is midway between two AWG sizes, it is listed and being ">" one AWG and "<" another AWG. Cables sold in Europe are normally labeled according to the combined cross section of all strands in mm², which can be compared directly with the Area column.

In the North American electrical industry, conductors larger than 4/0 AWG are generally identified by the area in thousands of circular mils (kcmil), where 1 kcmil = 0.5067 mm². A circular mil is the area of a wire one mil in diameter. One million circular mils is the area of a rod with 1000 mil = 1 inch diameter. An older abbreviation for one thousand circular mils is mcm. The term "mil" is capable of being misinterpreted because the term "mil" is used sometimes as a colloquial term for millimeter, milliliter, and so-forth.

Outside North America, wire sizes for electrical purposes are usually given as the cross sectional area in square millimeters. International standard manufacturing sizes for conductors in electrical cables are defined in IEC 60228.

WIRE GAUGE SELECTION TABLE Example of use: a 12v circuit which is 15 feet long and is to carry 10 amps should use at least AWG #16 gauge wire.
Circuit Amperes		Circuit Watts		Wire gauge (for length in feet)
6V	12V	6V	12V	3'	5'	7'	10'	15'	20'	25'
0 to 2.5	0 to 5	15	30	18	18	18	18	18	18	18
3.0	6	18	36	18	18	18	18	18	18	16
3.5	7	21	42	18	18	18	18	18	18	16
4.0	8	24	48	18	18	18	18	18	16	16
5.0	10	30	60	18	18	18	18	16	16	16
5.5	11	33	66	18	18	18	18	16	16	14
6.0	12	36	72	18	18	18	18	16	16	14
7.5	15	45	90	18	18	18	18	14	14	12
9.0	18	54	108	18	18	16	16	14	14	12
10	20	60	120	18	18	16	16	14	12	10
11	22	66	132	18	18	16	16	12	12	10
12	24	72	144	18	18	16	16	12	12	10
15	30	90	180	18	16	16	14	10	10	10
20	40	120	240	18	16	14	12	10	10	8
25	50	150	300	16	14	12	12	10	10	8
50	100	300	600	12	12	10	10	6	6	4
75	150	450	900	10	10	8	8	4	4	2
100	200	600	1200	10	8	8	6	4	4	2

AWG - American Wire Gauge (also known as B&S - Browne & Sharpe)
SWG - Standard Wire Gauge (also known as BIS - British Imperial Standard)

Further charts can be found here
and here (Wikipedia)