Standard Metal Gauges and Thickness

When using the following tables, remember that sheet metal gauge is legally defined by its weight per square foot - not by its thickness. The data in this first table is taken directly from the United States Code (USC Title 15, Chapter 6, Subchapter III, Section 206) which governs weights and measures with respect to trade in the US. All corresponding thicknesses are approximate (noted as such in the USC), and evidently rounded to the nearest simple fraction for ease of use - probably because in the time when this code was originally written (circa 1893), accurate measuring devices were not as common as they are today. These fractions are off a bit, (about 4.4% too thick) but may be "accurized" by making use of a correction factor of 0.956

These approximate thicknesses are based upon a 12"x12"x1" slab of steel weighing approximately 40.0 lbs (as implied by the entry for 24 gauge metal). The 0.956 correction factor is rooted in the idea that a slab of steel 12"x12"x1" actually weighs 41.84 lbs - meaning that a 12"x12" square of 24 gauge steel is, in reality, 1/41.84 inch thick ... not 1/40 inch, as might be inferred from the table, were it not understood that these are approximate thicknesses.

As mentioned before, a correction factor of 0.956 may be applied to correct these numbers. For example, in the case of 24 gauge sheet metal, the approximate thickness is listed as 1/40 or 0.025 inch. Using the correction factor gives us (0.956 * 0.025in) = 0.0239in ... an accurate number. Corrected thicknesses can be found in the second table.

The numbers in this first table apply only to plain steel or iron. Galvanized steel, such as is found in garage door sections, will be somewhat thicker for a given gauge, as can be seen in the second table.

A color key has been provided that shows how the gauges are bracketed into seven different groups. Within each group, adjacent gauges differ by a fixed interval - measured in oz/ft^2. Gauges that border two groups are shown in white.

Color Key:
20 oz 10 oz 5 oz 4 oz 2 oz 1 oz 1/2 oz 1/4 oz
Thickness Weight
Gauge# Inch Inch mm oz/ft^2 lbs/ft^2 kg/ft^2 kg/m^2 lbs/m^2
0000000 1/2 .5 12.7 320 20.00 9.072 97.65 215.28
000000 15/32 .46875 11.90625 300 18.75 8.505 91.55 201.82
00000 7/16 .4375 11.1125 280 17.50 7.983 85.44 188.37
0000 13/32 .40625 10.31875 260 16.25 7.371 79.33 174.91
000 3/8 .375 9.525 240 15 6.804 73.24 161.46
00 11/32 .34375 8.73125 220 13.75 6.237 67.13 148.00
0 5/16 .3125 7.9375 200 12.50 5.67 61.03 134.55
1 9/32 .28125 7.14375 180 11.25 5.103 54.93 121.09
2 17/64 .265625 6.746875 170 10.625 4.819 51.88 114.37
3 1/4 .25 6.35 160 10 4.536 48.82 107.64
4 15/64 .234375 5.953125 150 9.375 4.252 45.77 100.91
5 7/32 .21875 5.55625 140 8.75 3.969 42.72 94.18
6 13/64 .203125 5.159375 130 8.125 3.685 39.67 87.45
7 3/16 .1875 4.7625 120 7.5 3.402 36.62 80.72
8 11/64 .171875 4.365625 110 6.875 3.118 33.57 74.00
9 5/32 .15625 3.96875 100 6.25 2.835 30.52 67.27
10 9/64 .140625 3.571875 90 5.625 2.552 27.46 60.55
11 1/8 .125 3.175 80 5 2.268 24.41 53.82
12 7/64 .109375 2.778125 70 4.375 1.984 21.36 47.09
13 3/32 .09375 2.38125 60 3.75 1.701 18.31 40.36
14 5/64 .078125 1.984375 50 3.125 1.417 15.26 33.64
15 9/128 .0703125 1.7859375 45 2.8125 1.276 13.73 30.27
16 1/16 .0625 1.5875 40 2.5 1.134 12.21 26.91
17 9/160 .05625 1.42875 36 2.25 1.021 10.99 24.22
18 1/20 .05 1.27 32 2 .9072 9.765 21.53
19 7/160 .04375 1.11125 28 1.75 .7938 8.544 18.84
20 3/80 .0375 .9525 24 1.50 .6804 7.324 16.15
21 11/320 .034375 .873125 22 1.375 .6237 6.713 14.80
22 1/32 .03125 .793750 20 1.25 .567 6.103 13.46
23 9/320 .028125 .714375 18 1.125 .5103 5.493 12.11
24 1/40 .025 .635 16 1 .4536 4.882 10.76
25 7/320 .021875 .555625 14 .875 .3969 4.272 9.42
26 3/160 .01875 .47625 12 .75 .3402 3.662 8.07
27 11/640 .0171875 .4365625 11 .6875 .3119 3.357 7.40
28 1/64 .015625 .396875 10 .625 .2835 3.052 6.73
29 9/640 .0140625 .3571875 9 .5625 .2551 2.746 6.05
30 1/80 .0125 .3175 8 .5 .2268 2.441 5.38
31 7/640 .0109375 .2778125 7 .4375 .1984 2.136 4.71
32 13/1280 .01015625 .25796875 61/2 .40625 .1843 1.983 4.37
33 3/320 .009375 .238125 6 .375 .1701 1.831 4.04
34 11/1280 .00859375 .21828125 51/2 .34375 .1559 1.678 3.70
35 5/640 .0078125 .1984375 5 .3125 .1417 1.526 3.36
36 9/1280 .00703125 .17859375 41/2 .28125 .1276 1.373 3.03
37 17/2560 .006640625 .168671875 41/4 .265625 .1205 1.297 2.87
38 1/160 .00625 .15875 4 .25 .1134 1.221 2.69

Metal Gauge Table - Including Galvanized Steel and Aluminum

Gauge (ga) Standard Steel Thickness (inches) Galvanized Steel Thickness (inches) Aluminum Thickness (inches)
3 0.2391 0.2294
4 0.2242 0.2043
5 0.2092 0.1819
6 0.1943 0.1620
7 0.1793 0.1443
8 0.1644 0.1285
9 0.1495 0.1532 0.1144
10 0.1345 0.1382 0.1019
11 0.1196 0.1233 0.0907
12 0.1046 0.1084 0.0808
13 0.0897 0.0934 0.0720
14 0.0747 0.0785 0.0641
15 0.0673 0.0710 0.0571
16 0.0598 0.0635 0.0508
17 0.0538 0.0575 0.0453
18 0.0478 0.0516 0.0403
19 0.0418 0.0456 0.0359
20 0.0359 0.0396 0.0320
21 0.0329 0.0366 0.0285
22 0.0299 0.0336 0.0253
23 0.0269 0.0306 0.0226
24 0.0239 0.0276 0.0201
25 0.0209 0.0247 0.0179
26 0.0179 0.0217 0.0159
27 0.0164 0.0202 0.0142
28 0.0149 0.0187 0.0126
29 0.0135 0.0172 0.0113
30 0.0120 0.0157 0.0100
31 0.0105 0.0142 0.0089
32 0.0097 0.0134 0.0080
33 0.0090 0.0071
34 0.0082 0.0063
35 0.0075 0.0056
36 0.0067
37 0.0064
38 0.0060

Aluminum thickness information derived from Engineers Edge and Online Conversion