BWG to MM Chart (Gauges 0-36)

The Birmingham Wire Gauge (BWG) is a system used to specify the wall thickness of tubes, particularly in the heat exchanger, boiler, and condenser industries. Originating as a wire diameter measurement standard, BWG has been widely adopted in tube manufacturing to define wall thickness in a standardized way. A lower BWG gauge number indicates a thicker wall, while higher gauge numbers correspond to thinner walls.

BWG to MM Conversion Chart

BWG Gauge	Thickness (inch)	Thickness (mm)
0000	0.454	11.532
000	0.425	10.795
00	0.380	9.652
0	0.340	8.636
1	0.300	7.620
2	0.284	7.214
3	0.259	6.579
4	0.238	6.045
5	0.220	5.588
6	0.203	5.156
7	0.180	4.572
8	0.165	4.191
9	0.148	3.759
10	0.134	3.404
11	0.120	3.048
12	0.109	2.769
13	0.095	2.413
14	0.083	2.108
15	0.072	1.829
16	0.065	1.651
17	0.058	1.473
18	0.049	1.245
19	0.042	1.067
20	0.035	0.889
21	0.032	0.813
22	0.028	0.711
23	0.025	0.635
24	0.022	0.559
25	0.020	0.508
26	0.018	0.457
27	0.016	0.406
28	0.014	0.356
29	0.013	0.330
30	0.012	0.305
31	0.010	0.254
32	0.009	0.229
33	0.008	0.203
34	0.007	0.178
35	0.005	0.127
36	0.004	0.102

Notes

• BWG is the most commonly used gauge system in the United States for specifying tube wall thickness, especially for heat exchanger tubes, condenser tubes, and boiler tubes.
• The most frequently specified gauges for industrial tubing are BWG 10 through BWG 22. Heat exchanger tubes typically range from BWG 12 (2.769 mm) to BWG 16 (1.651 mm), depending on the service conditions and the required pressure rating.
• BWG should not be confused with SWG (Standard Wire Gauge), which is primarily used in the United Kingdom and Commonwealth countries. For the same gauge number, BWG and SWG define different thicknesses.
• Applicable material standards for tubes specified by BWG include ASTM A179 (carbon steel heat exchanger tubes), ASTM A213 (alloy and stainless steel tubes), and ASTM A249 (welded stainless steel tubes).
• When ordering tubes, always specify the gauge system explicitly (BWG or SWG) alongside the tube OD and material grade to avoid dimensional mismatches.