Sheet Metal Gauge Chart (Ga. Thickness & History You Should Know)

Gauge definition

GAUGE (abbreviated as Ga.), Which Americans call, is a unit of measurement of diameter that originated in North America and belongs to the Browne & Sharpe measurement system.

The larger the number of GAUGE is, the smaller the diameter is. It is also used to indicate thickness after promotion.

Sheet Metal Gauge Sizes Chart In Inch and mm

There is no conversion formula due to the difference between Ga. scale and inch. The comparison of different unit systems is shown in the table below.

Metal Gage

Steel Gauge Chart (Manufacturers’ Standard) in. (mm)

Gauge No.Thickness in. (mm)
7/0(0000000)
6/0(000000)
5/0(00000)
4/0(0000)
3/0(000)
2/0(00)
1/0(0)
1
2
30.23916.0731
40.22425.6947
50.20925.3137
60.19434.9352
70.17934.5542
80.16444.1758
90.14953.7973
100.13453.4163
110.11963.0378
120.10462.6568
130.08972.2784
140.07471.8974
150.06731.7094
160.05981.5189
170.05381.3665
180.04781.2141
190.04181.0617
200.03590.9119
210.03290.8357
220.02990.7595
230.02690.6833
240.02390.6071
250.02090.5309
260.01790.4547
270.01640.4166
280.01490.3785
290.01350.3429
300.0120.3048
310.01050.2667
320.00970.2464
330.0090.2286
340.00820.2083
350.00750.1905
360.00670.1702
370.00640.1626
380.0060.1524
39
40

Galvanized Sheet Gauge Chart in. (mm)

Gauge No.Thickness in. (mm)
7/0(0000000)
6/0(000000)
5/0(00000)
4/0(0000)
3/0(000)
2/0(00)
1/0(0)
1
2
3
4
5
6
7
80.1681-4.2697
90.1532-3.8913
100.1382-3.5103
110.1233-3.1318
120.1084-2.7534
130.0934-2.3724
140.0785-1.9939
150.071-1.8034
160.0635-1.6129
170.0575-1.4605
180.0516-1.3106
190.0456-1.1582
200.0396-1.0058
210.0366-0.9296
220.0336-0.8534
230.0306-0.7772
240.0276-0.701
250.0247-0.6274
260.0217-0.5512
270.0202-0.5131
280.0187-0.475
290.0172-0.4369
300.0157-0.3988
310.0142-0.3607
320.0134-0.3404
33
34
35
36
37
38
39
40

Stainless Steel Gauge Chart (U.S. Standard) in. (mm)

Gauge No.Thickness in. (mm)
7/0(0000000)0.512.7
6/0(000000)0.4687511.90625
5/0(00000)0.4377511.11885
4/0(0000)0.4062510.31875
3/0(000)0.3759.525
2/0(00)0.343758.73125
1/0(0)0.31257.9375
10.281257.14375
20.265636.74688
30.256.35
40.234385.95313
50.218755.55625
60.203135.15938
70.18754.7625
80.171884.36563
90.156253.96875
100.140633.57188
110.1253.175
120.109382.77813
130.093752.38125
140.078131.98438
150.070311.78594
160.06251.5875
170.056251.42875
180.051.27
190.043751.11125
200.03750.9525
210.034380.87313
220.031250.79375
230.028130.71438
240.0250.635
250.021880.55563
260.018750.47625
270.017190.43656
280.015630.39688
290.014060.35719
300.01250.3175
310.010940.27781
320.010160.25797
330.009380.23813
340.008590.21828
350.007810.19844
360.007030.17859
370.006640.16867
380.006250.15875
39
40

Aluminum Gauge Chart in. (mm)

Gauge No.Thickness in. (mm)
7/0(0000000)0.6513516.54439
6/0(000000)0.5800514.73324
5/0(00000)0.5165513.12034
4/0(0000)0.4611.684
3/0(000)0.4096410.40486
2/0(00)0.36489.26592
1/0(0)0.324868.25144
10.28937.34822
20.257636.5438
30.229425.82727
40.204315.18947
50.181944.62128
60.162024.11531
70.144283.66471
80.128493.26365
90.114432.90652
100.101892.58801
110.090742.30485
120.080812.05252
130.071961.82781
140.064081.62773
150.057071.44953
160.050821.29083
170.045261.14953
180.04031.0237
190.035890.91161
200.031960.81181
210.028460.72293
220.025350.64381
230.022570.5733
240.02010.51054
250.01790.45466
260.015940.40488
270.01420.36055
280.012640.32108
290.011260.28593
300.010030.25464
310.008930.22677
320.007950.20193
330.007080.17983
340.00630.16012
350.005610.1426
360.0050.127
370.004450.11311
380.003970.10071
390.003530.08969
400.003140.07986

Brass Gauge Chart (Brown & Sharpe) in. (mm)

Gauge No.Thickness in. (mm)
7/0(0000000)0.6513516.54439
6/0(000000)0.5800514.73324
5/0(00000)0.5165513.12034
4/0(0000)0.4611.684
3/0(000)0.4096410.40486
2/0(00)0.36489.26592
1/0(0)0.324868.25144
10.28937.34822
20.257636.5438
30.229425.82727
40.204315.18947
50.181944.62128
60.162024.11531
70.144283.66471
80.128493.26365
90.114432.90652
100.101892.58801
110.090742.30485
120.080812.05252
130.071961.82781
140.064081.62773
150.057071.44953
160.050821.29083
170.045261.14953
180.04031.0237
190.035890.91161
200.031960.81181
210.028460.72293
220.025350.64381
230.022570.5733
240.02010.51054
250.01790.45466
260.015940.40488
270.01420.36055
280.012640.32108
290.011260.28593
300.010030.25464
310.008930.22677
320.007950.20193
330.007080.17983
340.00630.16012
350.005610.1426
360.0050.127
370.004450.11311
380.003970.10071
390.003530.08969
400.003140.07986

Sheet Metal Gauge Chart

GAUGE (Ga.)SteelGalvanized SteelStainless SteelAluminumElectrical Steel
in (mm)in (mm)in (mm)in (mm)in (mm)
30.2391 (6.07)
40.2242 (5.69)
60.1943 (4.94)0.162 (4.1)
70.1793 (4.55)0.1875 (4.76)0.1443 (3.67)
80.1644 (4.18)0.1681 (4.27)0.1719 (4.37)0.1285 (3.26)
90.1495 (3.80)0.1532 (3.89)0.1563 (3.97)0.1144 (2.91)
100.1345 (3.42)0.1382 (3.51)0.1406 (3.57)0.1019 (2.59)
110.1196 (3.04)0.1233 (3.13)0.1250 (3.18)0.0907 (2.30)
120.1046 (2.66)0.1084 (2.75)0.1094 (2.78)0.0808 (2.05)
130.0897 (2.28)0.0934 (2.37)0.094 (2.4)0.072 (1.8)
140.0747 (1.90)0.0785 (1.99)0.0781 (1.98)0.0641 (1.63)
150.0673 (1.71)0.0710 (1.80)0.07 (1.8)0.057 (1.4)
160.0598 (1.52)0.0635 (1.61)0.0625 (1.59)0.0508 (1.29)
170.0538 (1.37)0.0575 (1.46)0.056 (1.4)0.045 (1.1)
180.0478 (1.21)0.0516 (1.31)0.0500 (1.27)0.0403 (1.02)
190.0418 (1.06)0.0456 (1.16)0.044 (1.1)0.036 (0.91)
200.0359 (0.91)0.0396 (1.01)0.0375 (0.95)0.0320 (0.81)
210.0329 (0.84)0.0366 (0.93)0.034 (0.86)0.028 (0.71)
220.0299 (0.76)0.0336 (0.85)0.031 (0.79)0.025 (0.64)0.0310 (0.787)
230.0269 (0.68)0.0306 (0.78)0.028 (0.71)0.023 (0.58)0.0280 (0.711)
240.0239 (0.61)0.0276 (0.70)0.025 (0.64)0.02 (0.51)0.0250 (0.64)
250.0209 (0.53)0.0247 (0.63)0.022 (0.56)0.018 (0.46)0.0197 (0.50)
260.0179 (0.45)0.0217 (0.55)0.019 (0.48)0.017 (0.43)0.0185 (0.47)
270.0164 (0.42)0.0202 (0.51)0.017 (0.43)0.014 (0.36)
280.0149 (0.38)0.0187 (0.47)0.016 (0.41)0.0126 (0.32)
290.0135 (0.34)0.0172 (0.44)0.014 (0.36)0.0113 (0.29)0.0140 (0.35)
300.0120 (0.30)0.0157 (0.40)0.013 (0.33)0.0100 (0.25)0.011 (0.27)
310.0105 (0.27)0.0142 (0.36)0.011 (0.28)0.0089 (0.23)0.0100 (0.25)
320.0097 (0.25)
330.0090 (0.23)0.009 (0.23)
340.0082 (0.21)
350.0075 (0.19)
360.0067 (0.17)0.007 (0.18)
370.0064 (0.16)
380.0060 (0.15)0.005 (0.127)



The history of Gauge

In fact, the use of “GAUGE” to indicate thickness can be traced back to the beginning of the American Industrial Revolution.

At the time, people who produced wire needed a way to quantify the products they sold.

Of course, the easiest method is the gravimetric method.

But if the buyer only proposes to buy 15 pounds of wire, but does not specify the diameter of the wire, it will also bring a lot of trouble.

Therefore, the wire craftsmen will report the diameter according to the number of wire drawing they have performed.

This is the origin of GAUGE.

Because each drawing will reduce the diameter of the wire, the more times it is drawn, the smaller the diameter of the wire.

Therefore, the larger the GAUGE number, the smaller the diameter of the corresponding wire.

At that time, steel mills found that it was easier to weigh than to measure thickness when rolling plates.

Therefore, similar to metal wires, steel plates can be sold using the unit area weight method.

The thinner the corresponding steel plate, the smaller the weight per square foot.

Therefore, steel mills believe that the most convenient way to specify the thickness of steel plates is to establish the steel plate’s GAUGE number system by referring to the GAUGE number system adopted by the wire industry.



As for the historical origin of the GAUGE number, it may be determined by the level of productivity development at that time.

In the United States in the 18th and 19th centuries, its industrial standards were almost blank, so each manufacturer had to develop its own standards.

Over time and the improvement of the industry level, the standards of these manufacturers have gradually become consistent, and the unified standard wire gauge (SWG), steel sheet material manufacturer’s standard gauge (MSG) and non-ferrous metals’ American Wire Gauge (AWG) have gradually been established.

Regarding GAUGE numbers, a confusing phenomenon is that when you change from one GAUGE number to the next GAUGE number, the change in thickness and weight per unit area is not constant.

In fact, if you graph these numbers, you will see an “exponential decay curve”.

In other words, the difference between consecutive GAUGE numbers becomes smaller as the GAUGE value increases.

For example, the difference between 10Ga. and 11Ga. is 0.0149″, while the difference between 35Ga. and 36Ga is only 0.0008″.

The reason for this difference can be traced back to the origin of the GAUGE number: wire making, which depends on the amount of reduction that can be achieved with each drawing.

In order to manufacture thin metal wires, wire craftsmen hope to reduce the cross-section as soon as possible. However, due to the limitation of the metallurgical mechanism of material deformation, the amount of diameter reduction in a single pass is limited.

Over time, the wire industry has determined the optimal number of times required for wire drawing.

This is the root cause of the exponential decay curve we see.

It should be noted that when the non-ferrous metal plate and the steel plate are both at a certain Ga. number, the thickness is actually different.

For example, 21Ga. corresponds to the standard steel thickness of 0.0329 inches (0.84mm); the corresponding galvanized steel thickness is 0.0366 inches (0.93mm), and the corresponding aluminum thickness is 0.028 inches (0.71mm).

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27 thoughts on “Sheet Metal Gauge Chart (Ga. Thickness & History You Should Know)”

  1. Please explain the difference between US CODE defined #8 gauge steel and iron sheet and plate at .1719″ vs this (and other steel charts) showing #8 steel circa .1614″.

    I have notice older goods specified per drawing made of #8 to be the thicker in earlier versions, and the thinner in later production to date.

    Is this cherry picking to save material cost while still claiming “in spec”?

    1. Not quite sure about the purpose to make it thinner, as you said, but the above data in the gauge chart is accurate.

  2. Thanks for the reply. I know the table you use is reproduced everywhere, used by various manufacturers…

    BUT, US CODE, STANDARD WEIGHTS AND MEASURES, has not changed, and until I can read of some separate established class of steel, is otherwise as if redefining the ounce or inch.

  3. gopinath elumalai

    Can you say me the conversion factor, that how are you converting gauge into mm/inch? (in sheet metal)

  4. If you are unfamiliar with the gauge system, this blog will explain the gauge system and includes a sheet metal gauge chart.

  5. It’s interesting to know that sheet metal products such as aluminum have different gauges such as inches and mm depending on where it is sourced from. I’m trying to create an ornate aluminum cart that I will use for my tea party set, so I was thinking of having this built by my husband. I think I’ll buy some of the material from a reliable supplier if we can find any.

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