Converting sheet metal gauge numbers to millimeters is as simple as following the chart below.  For a more comprehensive gauge chart you can check out our sheet metal gauge chart here.  This chart covers the common and uncommon sheet metal sizes for steel, aluminum and galvanized steel.  Typically the even number gauges are used more frequently.

Gauge #Standard Steel (mm)Non-Ferrous / Aluminum (mm)Galvanized Steel (mm)
000000-14.732-
00000-13.119-
0000-11.684-
000-10.404-
00-9.266-
0-8.252-
1-7.348-
2-6.543-
36.0735.827-
45.6955.189-
55.3144.620-
64.9354.115-
74.5543.665-
84.1763.2644.270
93.7972.9063.891
103.4162.5883.510
113.0382.3043.132
122.6572.0522.753
132.2781.8292.372
141.8971.6281.994
151.7091.4501.803
161.5191.2901.613
171.3671.1511.461
181.2141.0241.311
191.062.9121.158
20.912.8131.006
21.836.724.930
22.759.643.853
23.683.574.777
24.607.511.701
25.531.455.627
26.455.404.551
27.417.361.513
28.378.320.475
29.343.287.437
30.305.254.399
31.267.226.361
32.246.203.340
33.229.180-
34.208.160-
35.191.140-
36.170.127-
37.163.114-
38.152.102-
39-.089-
40-.079-