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Magnet Wire SWG to mm calculator

Magnet Wire SWG to mm calculator

The Standard Wire Gauge (SWG) is a historical system used predominantly in the United Kingdom and is often used for specifying magnet (enameled) wire diameters. It is distinct from the American Wire Gauge (AWG) system.

The SWG values do not follow a simple mathematical formula for conversion to millimeters; you must use a reference table. The higher the SWG number, the thinner the wire.

The n gauge wire’s cross sercional area An in square millimeters (mm2) is equal to pi divided by 4 times the square wire diameter d in millimeters (mm):
An (mm2) = (π/4)×dn2

SWG to mm conversion calculator

SWG to mm conversion chart

The current practice of the Institute of Electrical and Electronics Engineers (IEEE) is to reflect the American Wire Gauge in customary English units in parallel with metric units of measurement.

SWG # Diameter
(mm)		 Diameter
(inch)		 Area
(mm2)
4/0 10.160 0.4000 81.0732
3/0 9.449  0.3720 70.1202
2/0 8.839 0.3480 61.3643
0 8.230 0.3240 53.1921
1 7.620 0.3000 45.6037
2 7.010 0.2760 38.5989
3 6.401 0.2520 32.1780
4 5.893 0.2320 27.2730
5 5.385 0.2120 22.7735
6 4.877 0.1920 18.6793
7 4.470 0.1760 15.6958
8 4.064 0.1600 12.9717
9 3.658 0.1440 10.5071
10 3.251 0.1280 8.3019
11 2.946 0.1160 6.8183
12 2.642 0.1040 5.4805
13 2.337 0.0920 4.2888
14 2.032 0.0800 3.2429
15 1.829 0.0720 2.6268
16 1.626 0.0640 2.0755
17 1.422 0.0560 1.5890
18 1.219 0.0480 1.1675
19 1.016 0.0400 0.8107
20 0.914 0.0360 0.6567
21 0.813 0.0320 0.5189
22 0.711 0.0280 0.3973
23 0.610 0.0240 0.2919
24 0.559 0.0220 0.2452
25 0.5080 0.0200 0.2027
26 0.4572 0.0180 0.1642
27 0.4166 0.0164 0.1363
28 0.3759 0.0148 0.1110
29 0.3454 0.0136 0.0937
30 0.3150 0.0124 0.0779
31 0.2946 0.0116 0.0682
32 0.2743 0.0108 0.0591
33 0.2540 0.0100 0.0507
34 0.2337 0.0092 0.0429
35 0.2134 0.0084 0.0358
36 0.1930 0.0076 0.0293
37 0.1727 0.0068 0.0234
38 0.1524 0.0060 0.0182
39 0.1321 0.0052 0.0137
40 0.1219 0.0048 0.0117
41 0.1118 0.0044 0.0098
42 0.1016 0.0040 0.0081
43 0.0914 0.0036 0.0066
44 0.0813 0.0032 0.0052
45 0.0711 0.0028 0.0040
46 0.0610 0.0024 0.0029
47 0.0508 0.0020 0.0020
48 0.0406 0.0016 0.0013
49 0.0305 0.0012 0.0007
50 0.0254 0.0010 0.0005

Key Considerations for Magnet Wire

When dealing with magnet wire (enameled wire), note the following:

  1. Bare Conductor Diameter: The values in the table refer to the bare copper conductor diameter only, not the overall diameter.
  2. Overall Diameter: The overall diameter (including the enamel/insulation) will be slightly larger. This increase depends on the insulation grade (Grade 1 / Single Build, Grade 2 / Double Build, or Grade 3 / Triple Build) chosen by the manufacturer, which affects coil design and winding requirements.
  3. SWG vs. AWG: SWG is typically used in older specifications or in regions outside of North America. Be careful not to confuse it with AWG. For example, 42 SWG (≈0.102 mm) is a much thinner wire than 42 AWG (≈0.063 mm). Always confirm the standard being used.