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Import and Export Essentials: The Little-Known Gauge Number System

Category: Industry News Publish Time：2018-10-12

In American English, GAUGE (abbreviated as Ga.) is a unit of length for diameter originating in North America and belonging to the Browne&Sharpe measurement system. The larger the GAUGE number, the smaller the diameter. It has also been extended to represent thickness. Because the Ga. system is different from inches, there is no conversion formula. The following table shows the correspondence between different unit systems. Metal Sheet Ga. Number and Actual Thickness Comparison Table GAUGE(Ga.) Steel Galvanized Steel Stainless Steel Aluminum Electrical Steel in (mm) in (mm) in (mm) in (mm) in (mm)

　　In the United States, GAUGE (abbreviated as Ga.) is a unit of length measurement for diameter originating in North America and belonging to the Browne&Sharpe gauge system. The larger the GAUGE number, the smaller the diameter. It has also been extended to represent thickness. Because the Ga. system is different from inches, there is no conversion formula. The comparison between different unit systems is shown in the table below.

　　Metal Sheet Ga. Number vs. Actual Thickness

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)

　　In fact, the use of "GAUGE" to represent thickness can be traced back to the beginning of the Industrial Revolution in the United States. At that time, wire makers needed a way to quantify the products they sold. The simplest method was weighing, but if a buyer only wanted to buy 15 pounds of wire without specifying the diameter, it would cause considerable trouble. Therefore, wire makers would report the diameter based on the number of wire drawing operations they had performed, which is the origin of GAUGE. Since each drawing operation reduces the wire diameter, the more drawing operations, the smaller the wire diameter. Therefore, the larger the GAUGE number, the smaller the corresponding wire diameter.

　　At that time, steel mills found that weighing was easier than measuring thickness when rolling sheet metal. Therefore, similar to wire, steel sheets could be sold by unit area weight, and the thinner the steel sheet, the smaller the weight per square foot. Therefore, steel mills believed that the most convenient way to specify steel sheet thickness was to refer to the GAUGE number system used in the wire industry and establish their own GAUGE number system for steel sheets.

　　As for the historical origin of the GAUGE number, it may have been determined by the level of productivity development at that time. In the 18th and 19th centuries in the United States, industrial standards were almost blank, so each manufacturer had to set its own standards. Over time and with the improvement of industrial levels, these manufacturers' standards gradually converged, and a unified standard wire gauge (SWG), manufacturer's standard gauge (MSG) for steel plate materials, and American wire gauge (AWG) for non-ferrous metals were gradually established.

　　Regarding GAUGE numbers, a confusing phenomenon is that when you change from one GAUGE number to the next, the change in thickness and unit area weight is not constant. In fact, if you plot these numbers on a chart, you will see an "exponential decay curve".

　　In other words, the difference between consecutive GAUGE numbers decreases 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 drawing, which depends on the amount of diameter reduction achievable in each drawing operation.

　　In order to produce fine metal wires, wire makers hope to reduce the cross-sectional area as quickly as possible. However, due to the limitations of material deformation metallurgical mechanisms, the amount of diameter reduction in a single pass is limited. Over time, the wire industry has determined the optimal number of passes required for wire drawing. This is also the fundamental reason for the exponential decay curve we see.

　　It should be noted that the thicknesses of non-ferrous metal sheets and steel sheets are actually different when they have the same Ga number. For example, the standard steel thickness for 21 Ga is 0.0329 inches (0.84 mm); the galvanized steel thickness is 0.0366 inches (0.93 mm), and the aluminum thickness is 0.028 inches (0.71 mm).

Keywords: Import and Export Essentials: The Little-Known Gauge Number System

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