A table of the gauge numbers and wire diameters is shown below.[1][2] The basis of the system is the thou (or mil in US English), or 0.001 in. Sizes are specified as wire diameters, stated in thou and tenths of a thou (mils and tenths). The wire diameter diminishes with increasing size number. No. 7/0, the largest size, is 0.50 in. (500 thou or 12.7 mm) dia., No. 1 is 0.30 in. (300 thou), and the smallest, No. 50, is 0.001 in. (1 thou or 25.4 µm).
The system as a whole approximates an exponential curve, plotting diameter against gauge-number (each size is a approximately a constant multiple of the previous size). The weight per unit length diminishes by an average of approximately 20% at each step. Because the weight per unit length is related to the cross sectional area, and therefore to the square of the diameter, the diameter diminishes by approximately 10.6%:
However, the system is piecewise linear, only approximating the exponential curve loosely. Thus, it runs in constant steps of 0.4 thou (0.4 mil) through the range No. 49 - No. 39 and of 0.8 thou (0.8 mil) through No. 39 - No. 30.
More information SWG, (in) ...
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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