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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25 thoughts on “Sheet Metal Gauge Thickness Chart (Ga. History You Don’t 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. Angela Waterford

    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.

  6. 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!

  7. 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.

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