Ruthen Systems

Sheet Metal Gauge Chart and Converter

Look up what a sheet-metal gauge means in inches and millimetres — steel, or aluminium and other non-ferrous sheet — and what a galvanized gauge weighs, or find the nearest gauges to a thickness. Every number comes from a US government source you can open, named under its table.

The method behind it: What a sheet metal gauge number means — step by step, with sources.

Dimensions

Gauge system
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Results

Prints all four tables with their sources and notes on plain paper.

Preview

Steel sheet — US Standard (revised)

Gaugeinmmlb/ft²
3 0.2391 6.073 10.0000
4 0.2242 5.695 9.3750
5 0.2092 5.314 8.7500
6 0.1943 4.935 8.1250
7 0.1793 4.554 7.5000
8 0.1644 4.176 6.8750
9* 0.1494 3.795 6.2500
10 0.1345 3.416 5.6250
11 0.1196 3.038 5.0000
12 0.1046 2.657 4.3750
13 0.0897 2.278 3.7500
14* 0.0749 1.902 3.1250
15 0.0673 1.709 2.8125
16 0.0598 1.519 2.5000
17 0.0538 1.367 2.2500
18 0.0478 1.214 2.0000
19 0.0418 1.062 1.7500
20 0.0359 0.912 1.5000
21 0.0329 0.836 1.3750
22 0.0299 0.759 1.2500
23 0.0269 0.683 1.1250
24 0.0239 0.607 1.0000
25 0.0209 0.531 0.8750
26 0.0179 0.455 0.7500
27 0.0164 0.417 0.6875
28 0.0149 0.378 0.6250
29 0.0135 0.343 0.5625
30 0.0120 0.305 0.5000
31 0.0105 0.267 0.4375
32 0.0097 0.246 0.4063
33 0.0090 0.229 0.3750
34 0.0082 0.208 0.3438
35 0.0075 0.190 0.3125
36 0.0067 0.170 0.2813
37 0.0064 0.163 0.2656
38 0.0060 0.152 0.2500

Source: TO 1-1A-9 / NAVAIR 01-1A-9, the USAF / US Navy general-data handbook for metals (Change 3, 2020; approved for public release), Table A-34 “Comparative Table of Standard Gages”, column “United States Standard (Revised)”, p. A-51 — a weight-based gauge whose thickness the table calls approximate. * Printed as shown. Every other row of this column equals its weight divided by 41.82 lb/ft² per inch of thickness, to four places; for gauge 9 that gives 0.1495 and for gauge 14 0.0747, the figure more often quoted for 14 gauge. Use the one your supplier quotes.

Aluminium, copper and brass sheet — American Wire Gauge (Brown & Sharpe)

Gaugeinmm
00000.460011.684
0000.409610.405
000.36489.266
00.32498.251
10.28937.348
20.25766.544
30.22945.827
40.20435.189
50.18194.621
60.16204.115
70.14433.665
80.12853.264
90.11442.906
100.10192.588
110.09072.305
120.08082.053
130.07201.828
140.06411.628
150.05711.450
160.05081.291
170.04531.150
180.04031.024
190.03590.912
200.03200.812
210.02850.723
220.02530.644
230.02260.573
240.02010.511
250.01790.455
260.01590.405
270.01420.361
280.01260.321
290.01130.286
300.01000.255
310.00890.227
320.00800.202
330.00710.180
340.00630.160
350.00560.143
360.00500.127
370.00450.113
380.00400.101
390.00350.090
400.00310.080

Computed from the definition in NBS Handbook 100, Copper Wire Tables (1966), §2.2: No. 0000 is 0.4600 in, No. 36 is 0.0050 in, and the 38 sizes between them form a geometric progression, each 1.1229322 times the next (the 39th root of 92). The same gauge is used for copper, brass and aluminium sheet (NBS Circular 391, 1931, p. 14; Tables 13–14, pp. 16–17).

Galvanized steel sheet — by weight

Gaugelb/ft²oz/ft²kg/m²
87.03125112.534.33
96.40625102.531.28
105.7812592.528.23
115.1562582.525.18
124.5312572.522.12
133.9062562.519.07
143.2812552.516.02
152.9687547.514.49
162.6562542.512.97
172.4062538.511.75
182.1562534.510.53
191.9062530.59.31
201.6562526.58.09
211.5312524.57.48
221.4062522.56.87
231.2812520.56.26
241.1562518.55.65
251.0312516.55.04
260.9062514.54.42
270.8437513.54.12
280.7812512.53.81
290.7187511.53.51
300.6562510.53.20
310.593759.52.90
320.562509.02.75
330.531258.52.59
340.500008.02.44

The galvanized sheet gauge is a weight gauge: the 1893 weight plus 2.5 oz/ft², gauges 8 to 34 (NBS Circular 391, Standard Thicknesses, Weights, and Tolerances of Sheet Metal, 1931, pp. 10–11, Table 7). No primary public source we found prints a thickness for it.

US Standard Gauge as enacted, 1893

GaugeFraction of an inchinmmoz/ft²kg/m²
00000001/2.512.70032097.65
00000015/32.4687511.90630091.55
000007/16.437511.11228085.44
000013/32.4062510.31926079.33
0003/8.3759.52524073.24
0011/32.343758.73122067.13
05/16.31257.93820061.03
19/32.281257.14418054.93
217/64.2656256.74717051.88
31/4.256.35016048.82
415/64.2343755.95315045.77
57/32.218755.55614042.72
613/64.2031255.15913039.67
73/16.18754.76212036.62
811/64.1718754.36611033.57
95/32.156253.96910030.52
109/64.1406253.5729027.46
111/8.1253.1758024.41
127/64.1093752.7787021.36
133/32.093752.3816018.31
145/64.0781251.9845015.26
159/128.07031251.7864513.73
161/16.06251.5874012.21
179/160.056251.4293610.99
181/20.051.270329.765
197/160.043751.111288.544
203/80.03750.952247.324
2111/320.0343750.873226.713
221/32.031250.794206.103
239/320.0281250.714185.493
241/40.0250.635164.882
257/320.0218750.556144.272
263/160.018750.476123.662
2711/640.01718750.437113.357
281/64.0156250.397103.052
299/640.01406250.35792.746
301/80.01250.31882.441
317/640.01093750.27872.136
3213/1280.010156250.2586.51.983
333/320.0093750.23861.831
3411/1280.008593750.2185.51.678
355/640.00781250.19851.526
369/1280.007031250.1794.51.373
3717/2560.0066406250.1694.251.297
381/160.006250.15941.221

The Act of March 3, 1893 (27 Stat. 746), 15 U.S.C. §206, as printed in the US Code (2024, govinfo): “approximate thickness” for each gauge, defined by its weight. The thicknesses are the weight at 40 lb/ft² per inch — wrought iron at 480 lb/ft³ (NBS Circular 391, p. 4) — which is why steel sheet of the same gauge is thinner. A variation of 2½ % either way is allowed (15 U.S.C. §208).

How this tool is verified

  • The 1893 table is checked against the law’s own arithmetic: every printed fraction and decimal is the defining weight at 40 lb/ft² per inch, and every metric weight per square metre agrees with the converted figure to within 0.15 % (the law itself truncates or misprints a few, such as gauge 0000 at 79.33 kg/m² where the conversion gives 79.34).
  • The steel column is transcribed from the handbook twice — its text layer and its page image — and held to the 1893 weights gauge for gauge; the two values that break the column’s pattern are flagged, not silently corrected.
  • The American Wire Gauge is computed from its definition in NBS Handbook 100 and checked against the values printed in NBS Circular 391.

The method, the reports and the responsibility boundary are on the Verification page.

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Assumptions and limits

Read these before you cut anything. They describe exactly what this tool does and does not account for.

  • Every value is nominal, as printed or defined in the source named under its table. Real sheet varies: the 1893 law itself allows 2½ % either way, and mills and standards set their own tolerances.
  • A gauge number is not a thickness. The same number means different thicknesses in different systems — steel, galvanized and aluminium 16 gauge are three different sheets.
  • Steel sheet values are the “United States Standard (Revised)” column of the USAF / US Navy general-data handbook for metals (TO 1-1A-9). Two printed values differ from the rest of the column’s pattern and are shown as printed with a note.
  • Galvanized sheet is gauged by weight. No primary public source found gives its thickness, so the tool gives weight only.
  • Aluminium, copper and brass sheet use the American Wire Gauge, which is defined by a formula; the values are computed from that definition.

Output is a planning and fabrication aid. You are responsible for verifying dimensions, tolerances and material behaviour before production — full disclaimer.

Worked example

16 gauge, three ways.

  • Steel sheet0.0598 in · 1.519 mm
  • Aluminium (AWG)0.0508 in · 1.291 mm
  • The 1893 law1/16 in · 1.588 mm

By hand: 0.0598 × 25.4 = 1.519; the AWG figure is 0.005 × 92^(20/39) = 0.0508; the 1893 figure is its 40 oz/ft² = 2.5 lb/ft² at 40 lb/ft² per inch = 0.0625 in.

Method

Sources

All are US government works. NBS Circular 391 says itself that it records customary practice rather than setting a standard; treat every value here the same way — nominal, for identification, not for inspection.

Questions

How thick is 16 gauge steel?

In the steel sheet gauge used today, 16 gauge is 0.0598 in (1.519 mm) nominal. The 1893 law that created the gauge prints 1/16 in (1.5875 mm) for the same number, because it was based on wrought iron at 40 lb/ft² per inch; steel sheet of the same weight is thinner.

Why is aluminium 16 gauge thinner than steel 16 gauge?

Because it is a different gauge altogether. Aluminium, copper and brass sheet follow the American Wire Gauge (Brown & Sharpe), where 16 is 0.0508 in (1.291 mm). Steel follows the US Standard gauge, a weight-based system. Always say which.

Where do the numbers come from?

Only from documents a reader can open, all US government works: the 1893 Act in the US Code (15 U.S.C. §206), the USAF/Navy handbook TO 1-1A-9 Table A-34, and National Bureau of Standards publications (Handbook 100 for the American Wire Gauge, Circular 391 for galvanized weights). Each table names its source.

Should I order sheet by gauge?

Better by thickness in millimetres or inches, with the tolerance you need. A gauge is a shorthand whose meaning depends on the material and the supplier; a thickness is not.

What do I get in the CSV?

The selected table: gauge, nominal thickness in inches and millimetres, and weight per square foot where the source defines one.

Missing an option?

A different datum, an offset, a shop allowance, another shape altogether — say what this tool does not cover yet. Requests decide what gets built next, and a report of a wrong result is dealt with before anything new.

Request an option

Rather have the whole part drawn — a shop drawing or a cut file from your sketch? That is paid drafting, quoted per job: drafting for small shops.

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