Sheet Metal Gauge Calculator
Convert sheet metal gauge to thickness for steel, galvanised, stainless and aluminium - four different standards - with weight per sheet.
How to use this calculator
- 1Always set the material. It is the input that changes the answer, and it is the one people skip.
- 2Measure with a micrometer if you are going the other way. Callipers on sheet are easily a couple of thousandths out, which can be a whole gauge.
- 3Use the comparison table to see what the same gauge number means everywhere else - it is worth a look before ordering.
- 4Write the decimal thickness on the order alongside the gauge. It costs nothing and removes the ambiguity.
How the calculation works
Thickness = table lookup by gauge number AND material standard
Weight per sq ft = thickness (in) x 144 x density (lb/cu in)
Sheet weight = weight per sq ft x sheet area- Gauge
- A count of drawing operations, not a measurement. Higher numbers are thinner
- Standard
- Manufacturers’ Standard Gauge for steel, Galvanized Sheet Gauge for galvanised, a separate stainless standard, and American Wire Gauge for aluminium
- Density
- Steel 0.2836 lb per cubic inch, stainless 0.289, aluminium 0.0975
There is no formula that converts gauge to thickness. Each standard is a table, arrived at historically, and the numbers do not follow any clean progression.
Galvanised sheet gauge deliberately includes the zinc coating, so a galvanised sheet is thicker than a bare one at the same gauge number while the steel underneath is about the same.
Aluminium gauge is American Wire Gauge, which does follow a geometric progression - each gauge is a fixed ratio thinner than the last - because it was designed for successive wire-drawing dies.
Worked example
Sixteen gauge, four ways
- 1.Sixteen gauge bare carbon steel is 0.0598 in - 1.519 mm.
- 2.The same number in galvanised is 0.0635 in, because the gauge includes the zinc.
- 3.In stainless it is 0.0625 in, on a different standard again, and in aluminium 0.0508 in on American Wire Gauge.
- 4.That is a 25% spread between the thickest and the thinnest, all correctly described as sixteen gauge.
Result: 0.0598 in in steel - and 0.0508 to 0.0635 across the four standards
A sheet of 14 gauge galvanised
- 1.Fourteen gauge galvanised is 0.0785 in against 0.0747 for bare steel - the difference is the zinc coating, which the galvanised standard counts.
- 2.At 0.2836 lb per cubic inch that is 3.21 lb per square foot.
- 3.A 4 by 10 ft sheet is 40 square feet, so about 128 lb a sheet.
- 4.Four of them is over 500 lb, which is a third of a half-ton pickup from four sheets of what most people would call thin metal.
Result: 0.0785 in, about 128 lb a sheet
Working backwards from a micrometer reading
- 1.A micrometer reads 0.040 in on a piece of aluminium sheet.
- 2.On the aluminium standard, 18 gauge is 0.0403 in - within three ten-thousandths, so that is what it is.
- 3.The same 0.040 in in steel would be closest to 19 gauge at 0.0418, and in stainless to 19 gauge at 0.0437.
- 4.Which is why a gauge number written on a drawing without a material is not a specification.
Result: 18 gauge in aluminium - and a different number in every other standard
Why gauge runs backwards
Gauge numbers count operations, not thickness. The system comes from wire drawing, where stock was pulled through progressively smaller dies and each pass was one more gauge. A wire that had been through twenty dies was twenty gauge; one that had been through ten was ten gauge and considerably fatter.
Sheet metal inherited the convention when it inherited the mills, and the inversion came with it. It is why twenty-six gauge is flashing you can cut with tin snips and seven gauge is nearly a quarter inch of plate - and why the numbering feels wrong to everybody the first several times they use it.
Because the numbers came from a physical process rather than a designed scale, the progressions are not clean either. There is no formula for the steel table; it is a list of numbers arrived at historically and then frozen. American Wire Gauge, used for aluminium sheet, is the exception - it is a genuine geometric progression, because it was designed rather than accumulated.
Four standards, one number
The unwelcome part is that the mills that adopted gauge did not adopt the same one. Carbon steel sheet uses the Manufacturers' Standard Gauge. Galvanised sheet uses the Galvanized Sheet Gauge, which is the same steel with the zinc coating counted in, so it reads thicker at every number. Stainless has a standard of its own. Aluminium borrowed American Wire Gauge.
At sixteen gauge those give 0.0598, 0.0635, 0.0625 and 0.0508 inches respectively. The spread is a quarter, and every one of them is correctly described as sixteen gauge. A drawing that calls out a gauge without a material has not specified a thickness.
It gets worse in the thin end, where the standards diverge further and where a few thousandths is a large proportion of the total. And it gets worse again with imported material, where a nominal metric thickness is sometimes described with the nearest gauge number for the domestic market.
- Carbon steel — Manufacturers’ Standard Gauge. The reference most people mean by default.
- Galvanised — Thicker at every gauge, because the number includes the zinc.
- Stainless — Its own standard, generally between bare steel and galvanised.
- Aluminium — American Wire Gauge - the thinnest at any given number, and a genuine geometric series.
What to do about it
Specify the decimal. Writing "16 ga (0.0598 in)" on a drawing or a purchase order takes a second, is understood by every supplier, and eliminates the ambiguity completely. If the supplier cannot work to a decimal thickness, that is information worth having early.
Measure with a micrometer rather than callipers when identifying unknown stock. Callipers on sheet, particularly on a burr or a slightly bowed piece, are easily two or three thousandths out, and in thin material that is a whole gauge number.
And be aware of what gauge is not. It is not a strength specification, it is not consistent across materials, and it says nothing about temper, finish or flatness. Two sheets of the same gauge in the same material can behave very differently in a brake if one is annealed and the other is half hard.
What this assumes, and where it stops
Assumptions
- Gauge tables are the standard published values for each of the four systems.
- Weights use standard densities for the material family - carbon steel for both bare and galvanised, 304 for stainless, 6061 for aluminium.
- Nominal thickness is used, with no allowance for rolling tolerance.
- Galvanised thicknesses include the zinc coating, which is how that standard is defined.
Limitations
- Galvanised weight is calculated at carbon steel density over the coated thickness, which slightly under-counts because zinc is a little less dense than steel. The error is well under a percent.
- Rolling tolerance means a real sheet varies from nominal by a few thousandths, and thin material varies proportionally more.
- Some suppliers, particularly for imported material, use nominal metric thicknesses labelled with the nearest gauge number. Those will not match the table.
- Gauge says nothing about temper, alloy, finish or flatness, all of which matter more than thickness for forming.
- Very thin foils and very heavy plate are outside the gauge system entirely and are specified in decimals.
Common questions
How thick is 16 gauge steel?
0.0598 inches, or 1.519 mm, in bare carbon steel. In galvanised it is 0.0635, in stainless 0.0625, and in aluminium 0.0508. The material has to be part of the answer - four separate standards are in daily use and they disagree by about a quarter at the same number.
Why is galvanised thicker than steel at the same gauge?
Because the Galvanized Sheet Gauge counts the zinc. The steel underneath a sheet of 16 gauge galvanised is roughly the same as bare 16 gauge steel; the extra 0.0037 inches is coating. It is a deliberate feature of the standard rather than a discrepancy.
Is a higher gauge number thicker or thinner?
Thinner. The numbering counts wire-drawing operations rather than measuring thickness, so more passes through smaller dies means a higher number and less metal. Twenty-six gauge is flashing; seven gauge is close to a quarter inch.
What gauge is 1/8 inch steel?
Nothing exactly. An eighth of an inch is 0.125, and the nearest steel gauges are 11 at 0.1196 and 10 at 0.1345 - neither is close. Once material gets to about an eighth inch the trade generally stops using gauge and specifies the decimal or the fraction, which is the sensible practice at any thickness.
How much does a sheet of 16 gauge steel weigh?
About 2.44 pounds per square foot, so a 4 by 8 sheet is around 78 pounds. The general figure is 40.8 pounds per square foot per inch of thickness for steel - multiply that by the decimal thickness for any gauge.
Sources
- Manufacturers’ Standard Gauge for sheet steel — American Iron and Steel Institute
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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