Steel Gauge Thickness Chart: Inches, mm & Weight by Gauge

Steel gauge is a numbering system for sheet thickness, not a unit of measurement. A higher gauge number means thinner material, the steps between numbers are not evenly spaced, and the thickness a given number stands for changes depending on whether the metal is carbon steel, galvanized steel, stainless steel or aluminium. Sixteen gauge carbon steel sheet is 0.0598 in (1.519 mm); 16 gauge stainless is 0.0625 in (1.587 mm); 16 gauge aluminium is 0.05082 in (1.291 mm).

That is the whole problem with gauge in one paragraph. This article gives the tables, explains where the numbers came from, and shows what the differences cost when a job is quoted from the wrong column.

Why a higher gauge number means thinner steel

Gauge numbers run backwards because they started as counts rather than dimensions. In the wire-drawing trades a gauge number recorded how many times a rod had been pulled through a reducing die. Each pass made the wire thinner, so a higher number described more passes and less material. Sheet gauge inherited the convention.

Nothing about the modern tables preserves a physical process, but the direction stuck. Ten gauge is thicker than 16 gauge, and 16 gauge is thicker than 20 gauge.

The spacing is also uneven. Between 10 and 12 gauge, carbon steel sheet drops 0.0299 in. Between 20 and 22 gauge it drops 0.0060 in. The same two-number step means five times as much material at the heavy end of the table as it does at the light end, which is why “two gauges thinner” is not a useful instruction on its own.

Where the steel gauge numbers actually come from

Two separate systems produced the numbers still in use on steel, and knowing which is which explains every discrepancy you will meet.

The US Standard Gauge was fixed by an Act of Congress on 3 March 1893 for levying duties on sheet iron and steel. It was defined by weight, not thickness, with the mass of a cubic foot of wrought iron taken as 480 lb. Sixteen gauge was set at 2.5 lb per square foot. Divide 2.5 by 40 lb/ft² per inch of thickness, which is what 480 lb/ft³ works out to, and 16 gauge lands on exactly 0.0625 in, or one sixteenth of an inch.

The Manufacturers’ Standard Gauge for sheet steel exists because almost no sheet was wrought iron. Rolled steel is denser, around 501.84 lb/ft³, which is 41.82 lb per square foot for each inch of thickness. Keeping the defined weight of each gauge and recalculating the thickness gives a thinner sheet for the same number:

16 gauge = 2.5 lb/ft2 ÷ 41.82 lb/ft2 per inch
         = 0.0598 in

The same result falls out of the ratio of the two densities: 480 ÷ 502 × 0.0625 in = 0.0598 in. Every number in the carbon steel column below is the US Standard Gauge value scaled by that ratio.

This is the reason two reputable charts can disagree about 16 gauge and both be right. One is quoting the 1893 weight standard, the other the manufacturers’ standard for steel sheet.

Steel gauge thickness chart: carbon and mild steel

These are Manufacturers’ Standard Gauge thicknesses, the figures used for uncoated carbon and mild steel sheet. Weights are calculated from the thickness at the density of rolled steel, 490 lb/ft³ and 7,850 kg/m³, the values ASTM A6/A6M adopts for rolled steel.

The metric column is the easiest to work from. Kilograms per square metre for steel is simply the thickness in millimetres multiplied by 7.85, so 16 gauge at 1.519 mm gives 11.92 kg/m² without any further arithmetic.

One caution on the weight columns. The Manufacturers’ Standard Gauge was defined at 41.82 lb/ft² per inch, which corresponds to 501.84 lb/ft³. Real carbon steel sheet is closer to 490 lb/ft³. The table above uses the real density, because that is what the sheet on the rack actually weighs. Charts that quote the defining weight instead will read about 2.4% heavier.

The gauge number means different thicknesses in different metals

This is where jobs go wrong. The same gauge number is a different thickness in each of the four common sheet materials, because each inherited a different system.

Three separate explanations sit behind those columns.

Stainless steel sheet kept the older numbers. Read the stainless column as fractions and the pattern appears immediately: 16 gauge is exactly 1/16 in, 14 gauge is 5/64 in, 12 gauge is 7/64 in, 10 gauge is 9/64 in. Those are the 1893 US Standard Gauge values, never rescaled for the density of rolled steel. Stainless runs about 4.5% thicker than carbon steel at every gauge number in the table.

Galvanized steel adds the coating. Subtract the carbon steel column from the galvanized column at any gauge and the answer is the same: 0.0037 to 0.0038 in, or roughly 0.094 mm. The galvanized sheet gauge was built by taking the steel gauge thickness and adding a fixed allowance for the zinc layer, which is why the two columns run parallel rather than diverging.

Aluminium uses a different system entirely. The aluminium column comes from the Brown and Sharpe series, a geometric progression with no relationship to the weight-based steel gauges. It is 11% to 24% thinner than carbon steel at the same number, and the gap is not constant, so no single conversion factor exists between them.

There is no universal gauge table. A chart that gives one thickness per gauge number without saying which metal it applies to is describing one column of the four.

Worked example: 16 gauge is not one sixteenth of an inch

The nominal equivalence that most people carry in their heads is off by more than it looks.

Known values: carbon steel sheet, 1,219 × 2,438 mm (a metric 4 × 8 ft sheet), density 7,850 kg/m³. Compare 16 gauge against a true 1/16 in.

16 gauge  = 0.0598 in × 25.4 = 1.5189 mm
1/16 inch = 0.0625 in × 25.4 = 1.5875 mm

Substitution, 16 gauge:

V = 1.219 m × 2.438 m × 0.0015189 m = 0.0045142 m3
m = 0.0045142 × 7,850 = 35.44 kg

Substitution, 1/16 in:

V = 1.219 m × 2.438 m × 0.0015875 m = 0.0047181 m3
m = 0.0047181 × 7,850 = 37.04 kg

Result: 1.60 kg per sheet, 4.52% of the total. Interpretation: on a 200 sheet order that is 320 kg unaccounted for. Reverse check: 1.5875 ÷ 1.5189 = 1.0452, and mass scales linearly with thickness, so 4.52% is right.

You can run the same comparison in the Steel Plate Weight Calculator by entering the two thicknesses in millimetres and leaving everything else alone.

Worked example: quoting a gauge order in the wrong metal

Known values: 100 sheets, 4 × 8 ft (32 ft² each), specified as 14 gauge. Estimated as mild steel, supplied as stainless.

Mild steel at 14 gauge:

t = 0.0747 in
w = 0.0747 × 40.833 lb/ft2 per inch = 3.050 lb/ft2
per sheet = 3.050 × 32 = 97.61 lb
100 sheets = 9,761 lb (4,427 kg)

Stainless at 14 gauge, which is 0.078125 in, and at 7.93 g/cm³ rather than 7.85:

w = 0.078125 × 40.833 × (7.93 ÷ 7.85) = 3.223 lb/ft2
per sheet = 3.223 × 32 = 103.12 lb
100 sheets = 10,312 lb (4,677 kg)

Result: 551 lb (250 kg) more than the estimate, 5.7% over. Interpretation: roughly four fifths of the error is the gauge table and only one fifth is the density. Reverse check: 0.078125 ÷ 0.0747 = 1.0459 for the thickness, 7.93 ÷ 7.85 = 1.0102 for the density, and 1.0459 × 1.0102 = 1.0566.

Material substitution on a gauge order changes the thickness as well as the density. Both have to be re-entered, not just the grade.

Worked example: converting a gauge specification to metric stock

Known values: a drawing calls for 10 gauge mild steel. The supplier quotes in millimetres.

10 gauge = 0.1345 in × 25.4 = 3.416 mm

Interpretation: the nearest common metric stock thicknesses are 3 mm and 4 mm. Three millimetres is 12.2% lighter per square metre than the specified sheet (23.55 kg/m² against 26.82), and 4 mm is 17.1% heavier (31.40 kg/m²). Neither is a substitute made without agreement, and both change the weight on the quotation.

Where a drawing carries a gauge number and the supply chain works in millimetres, convert once at the start, write the millimetre figure on the enquiry, and let the supplier confirm what they can actually roll. Reading and writing plate dimensions covers the notation that enquiry should use, and the metric and imperial size comparison covers the rest of the conversions.

Gauge tells you nominal thickness, not delivered thickness

A gauge number is a nominal value. The sheet supplied against it is produced to the thickness tolerance in its product specification, and that tolerance is what the material on the rack is actually held to.

This matters for weight in the obvious way: mass scales directly with thickness, so a sheet running at the top of its permitted range weighs proportionally more than the chart says. It matters for fabrication in a less obvious way, because press brake bend allowances, weld preparation and clearance fits are all sensitive to a few hundredths of a millimetre.

Ask for the thickness tolerance class or table on the order rather than assuming one. ASTM A6/A6M plate thickness tolerances and EN 10029 plate tolerances both cover plate rather than sheet, but they show how the permitted variation is structured, and sheet specifications work the same way with different numbers.

Nothing here is manufacturing error. Tolerance is a permitted variation written into the specification, agreed before the steel is rolled.

When gauge stops and plate begins

Gauge is a sheet convention. Above a certain thickness the product is ordered by a decimal or fractional thickness instead, and gauge numbers disappear from the paperwork.

There is no single dividing line that applies everywhere. ASTM A6/A6M classifies hot-rolled flat steel ordered to thickness as plate when it is over 8 in (200 mm) wide and 0.230 in (6 mm) or over in thickness, or over 48 in (1,200 mm) wide and 0.180 in (4.5 mm) or over in thickness. Commercial practice in many stockholders puts the line at 1/4 in or 6 mm. Both are in use.

In practice the gauge tables run out around 3 gauge, which is 0.2391 in, and anything heavier is quoted as a thickness. Steel plate versus steel sheet works through where the boundary sits and why suppliers disagree about it.

How to order without the gauge problem

Four habits remove almost all of the risk.

Write the thickness, not just the gauge. “16 gauge (0.0598 in / 1.519 mm) carbon steel” cannot be read off the wrong column. A gauge number alone can.

Name the material in the same breath. The gauge number is meaningless without it, and the four common sheet metals give four different answers.

Convert once, at the start. Carry the decimal or millimetre value through the estimate, the cutting list and the purchase order. Converting repeatedly is how rounding errors accumulate.

Check the weight against the area. A quick multiplication catches a wrong-column error immediately: thickness in millimetres × 7.85 gives kilograms per square metre for steel, and the sheet area follows from there.

Steel gauge FAQs

Is 10 gauge thicker than 16 gauge? Yes. Gauge numbers run in reverse, so a lower number is thicker material. Ten gauge carbon steel is 0.1345 in (3.416 mm) and 16 gauge is 0.0598 in (1.519 mm), which makes 10 gauge more than twice as thick.

How thick is 16 gauge steel in mm? Carbon steel sheet at 16 gauge is 1.519 mm. Galvanized steel at the same number is 1.613 mm and stainless is 1.587 mm, so the answer depends on the material as well as the gauge.

Why is 16 gauge steel not exactly 1/16 inch? Because the 1893 US Standard Gauge fixed 16 gauge by weight, at 2.5 lb/ft², assuming wrought iron at 480 lb/ft³. Rolled steel is denser, so keeping the same weight gives a thinner sheet: 480 ÷ 502 × 0.0625 in = 0.0598 in.

Can I use one gauge chart for every metal? No. Carbon steel, galvanized steel, stainless steel and aluminium use different gauge systems, and a single number can mean four different thicknesses. Always check which metal a chart covers before you read a value from it.

How do I work out the weight of a gauge sheet? Convert the gauge to a thickness first, then treat it as any other flat product. In metric, kilograms per square metre equals the thickness in millimetres multiplied by 7.85 for steel. In imperial, pounds per square foot equals the thickness in inches multiplied by 40.83.

Convert first, calculate second

Gauge is a label on a table, and the table depends on the metal. Get the thickness out of the number before anything else happens to the job, write it down in the unit the rest of the work will use, and the gauge system stops being a source of error.

Once you have a thickness, the weight is ordinary arithmetic. Put it into the Steel Plate Weight Calculator with the sheet dimensions and grade to get the figure for a quotation, or use the kilograms per square metre column above for a quick check.

Gauge thicknesses in this article are cross-checked against the Metal Supermarkets sheet metal gauge chart, and the historical basis against the collected sheet metal gauge notes at yarchive. The density used for the weight columns, 490 lb/ft³ and 7,850 kg/m³, is the value adopted in ASTM A6/A6M for rolled steel.