SWG Full Form: Standard Wire Gauge

Quick Answer

SWG stands for Standard Wire Gauge (also known as Imperial Wire Gauge or Stubs Iron Wire Gauge). It is a British gauge system used to specify wire diameters and tube wall thicknesses. SWG is defined by BS 3737 and is primarily used in the United Kingdom and Commonwealth countries. For the same gauge number, SWG and BWG values differ.

The SWG full form (Standard Wire Gauge) identifies a measurement system that originated in the British wire and sheet metal industry. In modern industrial applications, SWG is used alongside BWG (Birmingham Wire Gauge) to specify the wall thickness of tubes for heat exchangers, boilers, and instrumentation.

SWG vs BWG: Key Differences

While both systems use gauge numbers where lower numbers mean thicker material, the actual dimensions differ for each gauge number:

Gauge Number	SWG (inch)	SWG (mm)	BWG (inch)	BWG (mm)	Difference (mm)
G. 10	0.128	3.251	0.134	3.404	0.153
G. 11	0.116	2.946	0.120	3.048	0.102
G. 12	0.104	2.641	0.109	2.769	0.128
G. 14	0.080	2.032	0.083	2.108	0.076
G. 16	0.064	1.625	0.065	1.651	0.026
G. 18	0.048	1.219	0.049	1.245	0.026
G. 20	0.036	0.914	0.035	0.889	0.025
G. 22	0.028	0.711	0.028	0.711	0.000

SWG Gauge Chart

SWG Gauge	Wall Thickness (inch)	Wall Thickness (mm)
G. 7	0.176	4.470
G. 8	0.160	4.064
G. 9	0.144	3.658
G. 10	0.128	3.251
G. 11	0.116	2.946
G. 12	0.104	2.641
G. 13	0.092	2.337
G. 14	0.080	2.032
G. 15	0.072	1.829
G. 16	0.064	1.625
G. 17	0.056	1.422
G. 18	0.048	1.219
G. 19	0.040	1.016
G. 20	0.036	0.914
G. 21	0.032	0.813
G. 22	0.028	0.711

Where SWG Is Used

Region/Industry	Gauge System	Notes
United Kingdom	SWG	Traditional standard, defined in BS 3737
India	SWG	Adopted from British standards; common in tubing specs
Australia/New Zealand	SWG	Historical British influence; gradually shifting to metric
United States	BWG	Dominant in TEMA heat exchanger specifications
Middle East EPC projects	BWG or SWG	Depends on the owner’s standard and engineering contractor
Electrical wire industry	SWG (UK) / AWG (US)	AWG (American Wire Gauge) is a separate system for electrical wire

Common Mistake

Ordering tubes specified as “Gauge 14” without specifying BWG or SWG. SWG 14 = 0.080” (2.032 mm) while BWG 14 = 0.083” (2.108 mm). This 0.076 mm difference affects pressure ratings and fit-up with ferrule compression fittings. Always state “BWG 14” or “SWG 14” explicitly on purchase orders and material requisitions.

For complete tubing dimension and weight tables by both BWG and SWG gauges, see the full BWG/SWG size charts.

Read the full guide to BWG/SWG tube sizes