The Weird Thing About Gauge
What is a gauge anyways, and why is it such a strange unit of measurement? Can we even call a gauge a form of measurement?
When ordering raw material supplies, such as Aluminum or Stainless Steel stock, the sizes are specified in standard units such as inches, using whole numbers and decimals to define the shape. For example, If you order a waterjet cut blank of Aluminum 6061-T6 that is 4.50” x 4.25” x 8.00”, then there is a reasonable expectation to get material that size on delivery. This is the industry standard for bar or plate stock materials, like those offered through Xometry Supplies. However, when it comes to sheet metal you will often hear materials referred to in gauge. What is a gauge anyways, and why is it such a strange unit of measurement? Can we even call a gauge a form of measurement?
Gauge was established in the first metal rolling mills of North America as a reference number, defined individually, which correlated with materials and thicknesses produced at that mill. Ultimately trade increased and these sizes became more agreed-upon, leaving the legacy that is used today. Also used for wire diameters, gauge units are more symbolic where they progressively represent thicker metal pieces the lower the number is, such as a 7 gage piece of steel at 0.1793” or the thinner 22 gauge at 0.0299”.
Compared to modern systems, gauge units can get even more confusing because thickness varies between materials of the same gauge. This is because gauge is correlated with weight. Also, gauge is defined differently between ferrous metals like steel and non-ferrous metals like aluminum. So a 12 gauge plate of steel is over 0.020” thicker than the same gauge aluminum. The lookup table below can be helpful when discussing gauge when providing sheet metal services. Note that this list is not comprehensive, for example, gauge has moved up to 0.5000” which naturally makes it 0000000 gauge. Yes, that is seven zeros with no decimals or commas.
| Gauge | Steel | Galvanized | Stainless | Aluminum |
|---|---|---|---|---|
Gauge 3 | Steel 0.2391 in. / 6.07 mm | Galvanized - | Stainless - | Aluminum - |
Gauge 4 | Steel 0.2242 in. / 5.69 mm | Galvanized - | Stainless - | Aluminum - |
Gauge 5 | Steel 0.2092 in. / 5.31 mm | Galvanized - | Stainless - | Aluminum - |
Gauge 6 | Steel 0.1943 in. / 4.94 mm | Galvanized - | Stainless - | Aluminum 0.1620 in. / 4.11 mm |
Gauge 7 | Steel 0.1793 in. / 4.55 mm | Galvanized - | Stainless 0.1875 in. / 4.76 mm | Aluminum 0.1443 in. / 3.67 mm |
Gauge 8 | Steel 0.1644 in. / 4.18 mm | Galvanized 0.1681 in. / 4.27 mm | Stainless 0.1719 in. / 4.37 mm | Aluminum 0.1285 in. / 3.26 mm |
Gauge 9 | Steel 0.1495 in. / 3.80 mm | Galvanized 0.1532 in. / 3.89 mm | Stainless 0.1563 in. / 3.97 mm | Aluminum 0.1144 in. / 2.91 mm |
Gauge 10 | Steel 0.1345 in. / 3.42 mm | Galvanized 0.1382 in. / 3.51 mm | Stainless 0.1406 in. / 3.57 mm | Aluminum 0.1019 in. / 2.59 mm |
Gauge 11 | Steel 0.1196 in. / 3.04 mm | Galvanized 0.1233 in. / 3.13 mm | Stainless 0.1250 in. / 3.18 mm | Aluminum 0.0907 in. / 2.30 mm |
Gauge 12 | Steel 0.1046 in. / 2.66 mm | Galvanized 0.1084 in. / 2.75 mm | Stainless 0.1094 in. / 2.78 mm | Aluminum 0.0808 in. / 2.05 mm |
Gauge 13 | Steel 0.0897 in. / 2.28 mm | Galvanized 0.0934 in. / 2.37 mm | Stainless 0.0940 in. / 2.39 mm | Aluminum 0.0720 in. / 1.83 mm |
Gauge 14 | Steel 0.0747 in. / 1.90 mm | Galvanized 0.0785 in. / 1.99 mm | Stainless 0.0781 in. / 1.98 mm | Aluminum 0.0641 in. / 1.63 mm |
Gauge 15 | Steel 0.0673 in. / 1.71 mm | Galvanized 0.0710 in. / 1.80 mm | Stainless 0.0700 in. / 1.78 mm | Aluminum 0.0570 in. / 1.45 mm |
Gauge 16 | Steel 0.0598 in. / 1.52 mm | Galvanized 0.0635 in. / 1.61 mm | Stainless 0.0625 in. / 1.59 mm | Aluminum 0.0508 in. / 1.29 mm |
Gauge 17 | Steel 0.0538 in. / 1.37 mm | Galvanized 0.0575 in. / 1.46 mm | Stainless 0.0560 in. / 1.42 mm | Aluminum 0.0450 in. / 1.14 mm |
Gauge 18 | Steel 0.0478 in. / 1.21 mm | Galvanized 0.0516 in. / 1.31 mm | Stainless 0.0500 in. / 1.27 mm | Aluminum 0.0403 in. / 1.02 mm |
Gauge 19 | Steel 0.0418 in. / 1.06 mm | Galvanized 0.0456 in. / 1.16 mm | Stainless 0.0440 in. / 1.12 mm | Aluminum 0.0360 in. / 0.91 mm |
Gauge 20 | Steel 0.0359 in. / 0.91 mm | Galvanized 0.0396 in. / 1.01 mm | Stainless 0.0375 in. / 0.95 mm | Aluminum 0.0320 in. / 0.81 mm |
Gauge 21 | Steel 0.0329 in. / 0.84 mm | Galvanized 0.0366 in. / 0.93 mm | Stainless 0.0340 in. / 0.86 mm | Aluminum 0.0280 in. / 0.71 mm |
Gauge 22 | Steel 0.0299 in. / 0.76 mm | Galvanized 0.0336 in. / 0.85 mm | Stainless 0.0310 in. / 0.79 mm | Aluminum 0.0250 in. / 0.64 mm |
Gauge 23 | Steel 0.0269 in. / 0.68 mm | Galvanized 0.0306 in. / 0.78 mm | Stainless 0.0280 in. / 0.71 mm | Aluminum 0.0230 in. / 0.58 mm |
Gauge 24 | Steel 0.0239 in. / 0.61 mm | Galvanized 0.0276 in. / 0.70 mm | Stainless 0.0250 in. / 0.64 mm | Aluminum 0.0200 in. / 0.51 mm |
Gauge 25 | Steel 0.0209 in. / 0.53 mm | Galvanized 0.0247 in. / 0.63 mm | Stainless 0.0220 in. / 0.56 mm | Aluminum 0.0180 in. / 0.46 mm |
Gauge 26 | Steel 0.0179 in. / 0.45 mm | Galvanized 0.0217 in. / 0.55 mm | Stainless 0.0190 in. / 0.48 mm | Aluminum 0.0170 in. / 0.43 mm |
Gauge 28 | Steel 0.0149 in. / 0.38 mm | Galvanized 0.0187 in. / 0.47 mm | Stainless 0.0160 in. / 0.41 mm | Aluminum 0.0126 in. / 0.32 mm |
Is gauge archaic? Sure. Is it still used? Sure—we see it often enough that it is worth understanding how to communicate gauge to customers and clients. Meanwhile, we will continue to use modern sheet metal stock sizes defined by decimal-based measurements with defined tolerances.
This article was brought to you by your local wire stripper.