The chart
The last column is the thickness as AC 43.13-1B prints it in its rivet tables. Those twelve decimals are Brown & Sharpe gauges rounded to three places: 0.032" is 20 gauge, 0.040" is 18 gauge, 0.064" is 14 gauge.
| Gauge | Inches | mm | As AC 43.13-1B writes it |
|---|---|---|---|
| 8 | 0.1285" | 3.26 | .128" |
| 9 | 0.1144" | 2.91 | — |
| 10 | 0.1019" | 2.59 | .102" |
| 11 | 0.0907" | 2.30 | .091" |
| 12 | 0.0808" | 2.05 | .081" |
| 13 | 0.0720" | 1.83 | — |
| 14 | 0.0641" | 1.63 | .064" |
| 15 | 0.0571" | 1.45 | — |
| 16 | 0.0508" | 1.29 | .051" |
| 17 | 0.0453" | 1.15 | — |
| 18 | 0.0403" | 1.02 | .040" |
| 19 | 0.0359" | 0.91 | .036" |
| 20 | 0.0320" | 0.81 | .032" |
| 21 | 0.0285" | 0.72 | — |
| 22 | 0.0253" | 0.64 | .025" |
| 23 | 0.0226" | 0.57 | — |
| 24 | 0.0201" | 0.51 | .020" |
| 25 | 0.0179" | 0.45 | — |
| 26 | 0.0159" | 0.40 | .016" |
| 27 | 0.0142" | 0.36 | — |
| 28 | 0.0126" | 0.32 | — |
| 29 | 0.0113" | 0.29 | — |
| 30 | 0.0100" | 0.25 | — |
Thicknesses calculated from the definition of the series: gauge 36 = 0.005", gauge 0000 = 0.460", with 39 equal ratio steps between them. A higher gauge number is a thinner sheet.
Find the gauge for a thickness
Measured a sheet, or have a metric thickness? Enter it to get the nearest gauge and the gauges either side.
How the series works
Each gauge is about 12.3% thicker than the next. The Brown & Sharpe series fixes two end points, 0.460" for gauge 0000 and 0.005" for gauge 36, and divides the range into equal ratios. The ratio is 1.1229. NBS Letter Circular 24 gives the useful consequence: the sixth power of that ratio is 2.005, so six gauges thicker is about twice the thickness, and twice the weight per square foot. 26 gauge is 0.0159"; 20 gauge is 0.0320"; 14 gauge is 0.0641".
Why steel is different. The same circular lists separate gauges for iron and steel sheet, for galvanized sheet and for tin plate, each built on its own basis. The numbers overlap but the thicknesses do not. Read 20 gauge off a steel chart and order it in aluminum, and you will not get 0.032".
Why aircraft data uses decimals. AC 43.13-1B, the FAA Airframe Handbook and the distributors in our catalog all call sheet out by decimal thickness — 0.032", 0.040", 0.063". A decimal can only mean one thing. A gauge number needs the series named before it means anything. Use the gauge to translate, and order and record by the decimal.
Where 0.063" comes from. Distributors list 0.063" where AC 43.13-1B writes 0.064". 14 gauge is 0.0641"; 0.063" is 1/16" rounded. Both name the same sheet, within mill tolerance.
Worked example
A European drawing calls for 0.8 mm sheet. What gauge is it, and is it the same as the 0.032" in a US repair?
- 0.8 mm ÷ 25.4 = 0.0315".
- 20 gauge is 0.0320" (0.81 mm). 0.0315" is about 1.5% thinner. It is the nearest gauge.
- 21 gauge is 0.0285", 19 gauge is 0.0359": no closer match.
- AC 43.13-1B tabulates 20 gauge as 0.032".
0.8 mm is close to 20 gauge but 0.0005" thinner than 0.032" nominal. For a repair specified as 0.032", 0.8 mm sheet is a substitution, and the call to make it belongs to whoever approves the repair — not to the gauge chart.
Limits — when NOT to use this chart
A conversion chart, not a material specification.
- Not for steel, stainless or titanium sheet. They use different gauge series. 4130 sheet is ordered by decimal thickness.
- Nominal, not measured. Rolled sheet carries a thickness tolerance. Check the actual sheet with a micrometer, not a gauge chart.
- Gauge does not identify the alloy or temper. 20 gauge 2024-T3, 6061-T6 and 5052-H32 are the same thickness and very different materials.
- The repair data governs. Where an SRM or AC 43.13-1B gives a thickness, use the decimal it gives, and the alloy and temper with it.
Questions people actually ask
What thickness is 20 gauge aluminum?
0.0320", or 0.81 mm. It is the sheet aircraft data calls 0.032".
Is 16 gauge aluminum the same as 16 gauge steel?
No. Aluminum follows the Brown & Sharpe series, where 16 gauge is 0.0508". Steel sheet has its own gauges, and a steel 16 gauge is a different thickness. Always ask which series a gauge number belongs to.
What gauge is 0.040 aluminum?
18 gauge, 0.0403". 0.025" is 22 gauge, 0.051" is 16 gauge and 0.064" is 14 gauge.
Why do the gauge steps get smaller as the sheet gets thinner?
Because each step is a fixed ratio, not a fixed amount. From 8 to 9 gauge the sheet loses 0.014"; from 29 to 30 it loses about 0.001". Each is about 11% of the thicker sheet.
Sources
- National Bureau of Standards, Letter Circular 24, Standard Thicknesses of Sheet Metal (rev. 1925) — “The American Wire Gage is extensively used in the United States for nearly all non-ferrous sheets, particularly copper, brass, aluminum…” Also the separate gauges for iron and steel sheet, galvanized sheet and tin plate, and the six-sizes-doubles rule.
- FAA AC 43.13-1B CHG 1, Chapter 4, Tables 4-9 to 4-11 — the twelve decimal sheet thicknesses in the last column of the chart.
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Chapter 4 — “The thickness of sheet metal, called gauge, ranges from 8 to 30 with the higher gauge denoting thinner metal.”