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?

By Greg Paulsen · January 14, 2020

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 Measurements Across Different Metals

Steel

Galvanized

Stainless

Aluminum

Gauge

in.

mm

in.

mm

in.

mm

in.

mm

3

0.2391

6.07







4

0.2242

5.69







5

0.2092

5.31







6

0.1943

4.94





0.1620

4.11

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

0.0940

2.39

0.0720

1.83

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

0.0700

1.78

0.0570

1.45

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

0.0560

1.42

0.0450

1.14

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

0.0440

1.12

0.0360

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

0.0340

0.86

0.0280

0.71

22

0.0299

0.76

0.0336

0.85

0.0310

0.79

0.0250

0.64

23

0.0269

0.68

0.0306

0.78

0.0280

0.71

0.0230

0.58

24

0.0239

0.61

0.0276

0.70

0.0250

0.64

0.0200

0.51

25

0.0209

0.53

0.0247

0.63

0.0220

0.56

0.0180

0.46

26

0.0179

0.45

0.0217

0.55

0.0190

0.48

0.0170

0.43

28

0.0149

0.38

0.0187

0.47

0.0160

0.41

0.0126

0.32


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.

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