SWG to mm: winding wire size chart for buyers

Most rewinding and transformer teams in India still order winding wire by SWG (Standard Wire Gauge). Designers and imported drawings often give the diameter in millimetres instead. Use the table below to convert, then specify the insulation grade and quantity.

British Standard Wire Gauge, nominal bare conductor diameter.
SWG	Bare diameter (mm)
8	4.064
10	3.251
11	2.946
12	2.642
13	2.337
14	2.032
15	1.829
16	1.626
17	1.422
18	1.219
19	1.016
20	0.914
21	0.813
22	0.711
23	0.610
24	0.559
25	0.508
26	0.457
27	0.417
28	0.376
29	0.345
30	0.315
31	0.295
32	0.274
33	0.254
34	0.234
35	0.213
36	0.193
37	0.173
38	0.152
39	0.132
40	0.122

The table gives the bare copper diameter. Enamel adds to the overall diameter, and the increase depends on the grade (for example single or dual coat), so check the overall diameter with your winding data when slot fill is tight.

What to put in the RFQ

Gauge (SWG) or bare diameter in mm, one line per size
Insulation / thermal class, for example Class F (155 °C) or Class H (180 °C)
Quantity in kg for each size
Preferred make, and whether alternatives are acceptable
Required date and delivery location

Half gauges

Half gauges such as 18.5 or 22.5 SWG are common in motor rewinding. List them exactly as your winding data states rather than rounding to the nearest full gauge.

Why rates change

Winding wire is priced mainly on copper, which moves daily. Treat every quotation's validity date as part of the price, and re-confirm the rate if you release the order after it expires.

Questions

Is 20 SWG thicker than 22 SWG?

Yes. In the SWG system a larger gauge number means a thinner wire: 20 SWG is 0.914 mm and 22 SWG is 0.711 mm bare diameter.

Should I order winding wire by kg or by metre?

Winding wire is normally bought by weight (kg). If your design gives a length, ask for the weight equivalent for the chosen gauge and grade.

Published 30 September 2026 by Kanoi Traders.