When working with sheet metal, it is common for the term “gauge” to be used. Someone unfamiliar with the gauge system may not understand what is meant by 18 gauge steel, for example. To help, this blog will explain the gauge system and features a sheet metal gauge chart.

How are sheet metal gauges used?

Gauges are used to specify the thickness of a sheet metal. Gauges are neither standard nor metric and the values are independent of those measurement systems. A gauge conversion chart can be used to determine the actual thickness of sheet metal in inches or millimeters. For example, 18 gauge steel, according to a gauge conversion chart, is 0.0478 inch or 1.214 millimeter. The gauge number “18” holds no relevance to the actual measurements.

There are several different gauge systems used today, with specific gauge designations used for specific metal types. For example, in one gauge system, 18 gauge steel measures 0.0478 inches thick, but 18 gauge aluminum is 0.0403 inches thick. Because of the varying thicknesses, a gauge chart should be used to ensure the metal meets the required dimensions.

History of the gauge system

The gauge system has long history in metal fabrication. It most likely originated from the British wire industry before the standard and metric measurement systems were widely adopted. At that time, gauges were used to describe the diameter of the metal wire being drawn. Since then, it has remained a prevalent method of designating the thickness of both wire and sheet metal.

Sheet Metal Gauge Charts

To determine what metal gauge you need, use these sheet metal gauge charts:

Jump to:
Carbon Steel Gauge Chart
Aluminum Gauge Chart
Stainless Steel Gauge Chart
Galvanized Steel Gauge Chart
Brass Gauge Chart
Copper Gauge Chart

Carbon Steel Gauge Chart
Gauge
Number
Inches Max / Min
(Inches)
MM Max / Min
(MM)
7 .1793 .1883 / .1703 4.554 4.78 / 4.32
8 .1644 .1734 / .1554 4.175 4.04 / 3.95
9 .1495 .1585 / .1405 3.797 4.03 / 3.56
10 .1345 .1405 / .1285 3.416 3.57 / 3.26
11 .1196 .1256 / .1136 3.038 3.19 / 2.89
12 .1046 .1106 / .0986 2.656 2.81 / 2.50
14 .0747 .0797 / .0697 1.897 2.02 / 1.77
16 .0598 .0648 / .0548 1.518 1.65 / 1.39
18 .0478 .0518 / .0438 1.214 1.32 / 1.11
20 .0359 .0389 / .0329 .911 .99 / .84
22 .0299 .0329 / .0269 .759 .84 / .68
24 .0239 .0269 / .0209 .607 .68 / .53
26 .0179 .0199 / .0159 .454 .51 / .40
28 .0149 .0169 / .0129 .378 .43 / .33

 

Aluminum Gauge Chart
Gauge
Number
Inches Tolerance
(Inches)
MM Tolerance
(MM)
7 .1443 .010 3.665 .25
8 .1285 .005 3.264 .013
9 .1144 .005 2.906 .13
10 .1019 .005 2.588 .13
11 .09074 .004 2.305 .10
12 .08081 .004 2.053 .10
14 .06408 .004 1.628 .10
16 .05082 .004 1.291 .10
18 .04030 .003 1.024 .076
20 .03196 .0025 .812 .064
22 .02535 .0025 .644 .064
24 .02010 .0025 .511 .064
26 .01594*   .405*  
28 .01264*   .321*  
30 .01003*   .255*  

 

Stainless Steel Gauge Chart
Gauge
Number
Inches Tolerance
(Inches)
MM Tolerance
(MM)
8 .17187 .0105 4.365 .2
9 .15625 .0105 3.968 .2
10 .14062 .009 3.571 .23
11 .125 .0075 3.175 .19
12 .10937 .007 2.778 .18
14 .07812 .0055 1.984 .14
16 .0625 .0045 1.587 .11
18 .050 .004 1.270 .10
20 .0375 .003 .9525 .076
22 .03125 .003 .7937 .076
24 .025 .002 .635 .051
26 .01875 .002 .476 .051
28 .01562*   .396*  
30 .0125*   .3175*  

 

Galvanized Steel Gauge Chart
Gauge
Number
Inches Max / Min
(Inches)
MM Max / Min
(MM)
8 .1681*   4.269*  
9 .1532*   3.891*  
10 .1382 .1472 /.1292 3.510 3.74 / 3.28
11 .1233 .1323 / .1143 3.1318 3.35 / 2.90
12 .1084 .1174 / .0994 2.753 2.98 / 2.52
14 .0785 .0865 / .0705 1.9939 2.20 / 1.79
16 .0635 .0695 / .0575 1.6129 1.77 / 1.46
18 .0516 .0566 / .0466 1.310 1.44 / 1.18
20 .0396 .0436 / .0356 1.005 1.11 / .90
22 .0336 .0376 / .0296 .853 .96 / .75
24 .0276 .0316 / .0236 .701 .80 / .60
26 .0217 .0247 / .0187 .551 .63 / .47
28 .0187 .0217 / .0157 .474 .55 / .40
30 .0157 .0187 / .0127 .398 .47 / .32

 

Brass Gauge Chart*
Gauge
Number
Inches MM
7 .1443 3.665
8 .1285 3.264
9 .1144 2.906
10 .1019 2.588
11 .09074 2.305
12 .08081 2.053
14 .06408 1.628
16 .05082 1.291
18 .04030 1.024
20 .03196 .812
22 .02535 .644
24 .02010 .511
26 .01594 .405
28 .01264 .321
30 .01003 .255

 

Copper Gauge Chart*
Gauge
Number
Inches MM
7 .180 4.572
8 .165 4.191
9 .148 3.759
10 .134 3.404
11 .120 3.048
12 .109 2.769
14 .083 2.108
16 .065 1.651
18 .049 1.245
20 .035 .889
22 .028 .711
24 .022 .559
26 .018 .457
28 .014 .356
30 .012 .305

 

*Actual thickness will vary due to tolerances.

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