Sheet Metal Gauge Thickness Chart (Ga. History You Don’t 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.

Sheet metal GAUGE thickness chart

GAUGE (Ga.) Steel Galvanized Steel Stainless Steel Aluminum Electrical Steel
in (mm) in (mm) in (mm) in (mm) in (mm)
3 0.2391 (6.07)
4 0.2242 (5.69)
6 0.1943 (4.94) 0.162 (4.1)
7 0.1793 (4.55) 0.1875 (4.76) 0.1443 (3.67)
8 0.1644 (4.18) 0.1681 (4.27) 0.1719 (4.37) 0.1285 (3.26)
9 0.1495 (3.80) 0.1532 (3.89) 0.1563 (3.97) 0.1144 (2.91)
10 0.1345 (3.42) 0.1382 (3.51) 0.1406 (3.57) 0.1019 (2.59)
11 0.1196 (3.04) 0.1233 (3.13) 0.1250 (3.18) 0.0907 (2.30)
12 0.1046 (2.66) 0.1084 (2.75) 0.1094 (2.78) 0.0808 (2.05)
13 0.0897 (2.28) 0.0934 (2.37) 0.094 (2.4) 0.072 (1.8)
14 0.0747 (1.90) 0.0785 (1.99) 0.0781 (1.98) 0.0641 (1.63)
15 0.0673 (1.71) 0.0710 (1.80) 0.07 (1.8) 0.057 (1.4)
16 0.0598 (1.52) 0.0635 (1.61) 0.0625 (1.59) 0.0508 (1.29)
17 0.0538 (1.37) 0.0575 (1.46) 0.056 (1.4) 0.045 (1.1)
18 0.0478 (1.21) 0.0516 (1.31) 0.0500 (1.27) 0.0403 (1.02)
19 0.0418 (1.06) 0.0456 (1.16) 0.044 (1.1) 0.036 (0.91)
20 0.0359 (0.91) 0.0396 (1.01) 0.0375 (0.95) 0.0320 (0.81)
21 0.0329 (0.84) 0.0366 (0.93) 0.034 (0.86) 0.028 (0.71)
22 0.0299 (0.76) 0.0336 (0.85) 0.031 (0.79) 0.025 (0.64) 0.0310 (0.787)
23 0.0269 (0.68) 0.0306 (0.78) 0.028 (0.71) 0.023 (0.58) 0.0280 (0.711)
24 0.0239 (0.61) 0.0276 (0.70) 0.025 (0.64) 0.02 (0.51) 0.0250 (0.64)
25 0.0209 (0.53) 0.0247 (0.63) 0.022 (0.56) 0.018 (0.46) 0.0197 (0.50)
26 0.0179 (0.45) 0.0217 (0.55) 0.019 (0.48) 0.017 (0.43) 0.0185 (0.47)
27 0.0164 (0.42) 0.0202 (0.51) 0.017 (0.43) 0.014 (0.36)
28 0.0149 (0.38) 0.0187 (0.47) 0.016 (0.41) 0.0126 (0.32)
29 0.0135 (0.34) 0.0172 (0.44) 0.014 (0.36) 0.0113 (0.29) 0.0140 (0.35)
30 0.0120 (0.30) 0.0157 (0.40) 0.013 (0.33) 0.0100 (0.25) 0.011 (0.27)
31 0.0105 (0.27) 0.0142 (0.36) 0.011 (0.28) 0.0089 (0.23) 0.0100 (0.25)
32 0.0097 (0.25)
33 0.0090 (0.23) 0.009 (0.23)
34 0.0082 (0.21)
35 0.0075 (0.19)
36 0.0067 (0.17) 0.007 (0.18)
37 0.0064 (0.16)
38 0.0060 (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).

The story of gauge.

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27 thoughts on “Sheet Metal Gauge Thickness Chart (Ga. History You Don’t Know)”

  1. This is the best explanation of gauges I’ve ever seen. Just when I would think I understood this, I’d end up questioning everything all over again, which is how I ended up here. So, thank you for the “Okay, NOW I get it!” moment! Makes perfect sense why it made no sense before, because it’s subjective, like lots of other American empirical systems. Again, thanks so much!

  2. Thank you for the informative information.
    But surely the most logical solution is for the US & Canada to change to the metric system?

    The UK & Europe have been metricated since 1969.
    This would surely save a lot of messing around as there are different thickness for different materials with the same gauge.

  3. The US is metric, and has been since the beginning of the metric system. Prior to the invention of the metric system the world was in chaos, with dozens of strange and incompatible and incommensurable systems of measurement in use. None of them were well-defined. Many countries, including the United States, saw the need in both commerce and in science for a single well-thought-out system of measurement. It took a long time, (France began working on it before 1700) but eventually a far superior system of weights and measures was worked out and entered into by treaty.
    In 1875, an international agreement, known as the Convention of the Metre, set up well defined metric standards for length and mass and established permanent mechanisms [commitees] to recommend and adopt further refinements in the metric system. This agreement, commonly called the ‘Treaty of the Meter’ in the United States, was signed by 17 countries, including the United States.
    So it can be said with complete correctness that the United States has always been “metric.” (The one unresolved dispute is the American insistence on using “.” as a decimal mark, whereas the Europeans prefer a “,” .)
    Why, then, is the U.S. civilian population still using the inch-pound and statute mile systems of units, when the rest of the world, including the United Kingdom, has converted to metric? Because American businesses three generations ago didn’t want to go to the expense of re-tooling, the American people two generations ago believed rumors (that the metric system was a subversive European plot) instead of looking at the science, and their legislators were not willing to force the issue. Still, among scientists, the metric system is used almost exclusively. It is simply better. All the “English” units are now defined in terms of metric primary standards. So for the public it will take longer, but we will get there. Nobody is forced to do anything they don’t want to. Get used to it at your own pace, but familiarity with all systems now in use will be an advantage to you.

  4. So, if I follow you correctly regarding how Gauge originated, the reason that the thickness of a given Gauge of different metals varies is a result of the different physical properties of a given metal. That is, how much of a size reduction can be made in a given pass through a die. As gold is an extremely ductile metal, I would expect that for a given wire diameter the Gauge of a gold wire would be less than for the same given diameter of an iron wire. That is the numeric value of the Gauge thickness of a gold wire would be smaller than for an equivalent diameter iron wire because you can have a greater diameter reduction with gold wire for a given draw because it is much more ductile than iron. Am I following your logic correctly or have I gone astray somewhere?

    If the Gauge is determined by the number of pulls, wouldn’t that mean that the diameter of different steel alloy compositions for the same Gauge would vary or has the use of Gauge now separated from the number of draws and that for a type of material, such as iron or steel over a fairly broad alloy range, the same thickness is assigned a “standard” Gauge number, even if the reality was that it might require a significant difference in the number of draws to get to the same diameter?

    Also, is the starting diameter of a stock rod standard over different metals? If it is not, then what is a Gauge value of zero. That is, it hasn’t been drawn at all? If you don’t have a standard starting diameter, it would seem that the same Gauge number could correspond to vastly different thicknesses depending on the diameter of your starting stock.

    Sorry, I’m not trying to be picky, as this was an informative post. I just find it fascinating and want to make sure that I correctly understand how this scale was developed and used.



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