British Standard Wire Gauge (often abbreviated to Standard Wire Gauge or SWG) is a unit for denoting wire size given by BS 3737:1964 (now withdrawn). It is also known as the Imperial Wire Gauge or British Standard Gauge. Use of SWG sizes has fallen greatly in popularity, but they are still used as a measure of thickness in guitar strings and some electrical wire. Cross sectional area in square millimetres is now the more usual size measurement for wires used in electrical installation cables. The current British Standard for metallic materials such as wire and sheet is BS 6722:1986, which is a solely metric standard.

British Standard Wire Gauge (SWG) diameters

SWG	(in)	(mm)	Step
7/0	0.500	12.700	0.036"/gauge
6/0	0.464	11.786	0.032"/gauge
5/0	0.432	10.973
4/0	0.400	10.160	0.028"/gauge
3/0	0.372	9.449	0.024"/gauge
2/0	0.348	8.839
0	0.324	8.230
1	0.300	7.620
2	0.276	7.010
3	0.252	6.401	0.020"/gauge
4	0.232	5.893
5	0.212	5.385
6	0.192	4.877	0.016"/gauge
7	0.176	4.470
8	0.160	4.064
9	0.144	3.658
10	0.128	3.251	0.012"/gauge
11	0.116	2.946
12	0.104	2.642
13	0.092	2.337
14	0.080	2.032	0.008"/gauge
15	0.072	1.829
16	0.064	1.626
17	0.056	1.422
18	0.048	1.219
19	0.040	1.016	0.004"/gauge
20	0.036	0.914
21	0.032	0.813
22	0.028	0.711
23	0.024	0.610	0.002"/gauge
24	0.022	0.559
25	0.020	0.5080
26	0.018	0.4572	0.0016"/gauge
27	0.0164	0.4166
28	0.0148	0.3759	0.0012"/gauge
29	0.0136	0.3454
30	0.0124	0.3150	0.0008"/gauge
31	0.0116	0.2946
32	0.0108	0.2743
33	0.0100	0.2540
34	0.0092	0.2337
35	0.0084	0.2134
36	0.0076	0.1930
37	0.0068	0.1727
38	0.0060	0.1524
39	0.0052	0.1321	0.0004"/gauge
40	0.0048	0.1219
41	0.0044	0.1118
42	0.004	0.1016
43	0.0036	0.0914
44	0.0032	0.0813
45	0.0028	0.0711
46	0.0024	0.0610
47	0.0020	0.0508
48	0.0016	0.0406
49	0.0012	0.0305	0.0002"/gauge
50	0.0010	0.0254

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