Sheet Metal Gauge Converter

Gauge number to thickness in millimetres and inches, and back — for uncoated steel, galvanised steel, stainless steel, aluminium, brass and copper. The point of the page is that these are four different answers: the gauge number was defined as a weight per square foot, so what it means in thickness depends on the metal.

Last updated 24 Sep 2026

Sheet metal gauges

Gauge ⇄ thickness, per metal

Which metal? (this is the control that matters)The gauge number means a different thickness in each of these, because the gauge scales were built from weight per unit area in different metals.

Which way?

Gauge number

Thickness (mm)Measure with a micrometer or vernier, away from an edge, and take the average of a few readings.

Not a circuit: what one gauge number means in four different gauge families, drawn to a single scale. The gauge number is a weight per unit area, so the thickness it implies depends on the metal — which is why a single sheet-metal gauge chart is always wrong for some material. Aluminium, brass and copper share one bar because they share the Brown & Sharpe scale; their WEIGHTS differ, and the table on the page gives those.

1.5184mmExample

16 gauge uncoated steel sheet

The gauge is a weight, not a thickness

uncoated steel: t (in) = W ÷ 41.82 · galvanised: t (in) = (W + 0.15625) ÷ 41.82 · stainless: t (in) = W ÷ 40 · aluminium, brass, copper: t (in) = 0.005 × 92^{(36 − n) / 39}

W: the Manufacturers’ Standard Gauge weight for that gauge number, in pounds per square foot
41.82: pounds per square foot per inch of steel — a density of 501.84 lb/ft³, the MSG basis
40: the same figure for the stainless table, a density of 480 lb/ft³
0.15625: pounds per square foot of zinc the traditional galvanised table allows for, about 0.0037 in
B and S: Brown & Sharpe, numerically identical to AWG, used for the non-ferrous sheet gauges

Worked example

16 gauge uncoated steel sheet
The Manufacturers' Standard Gauge weight for 16 gauge is 2.5 lb per square foot
Steel weighs 41.82 lb per square foot per inch, so t = 2.5 ÷ 41.82 = 0.0598 in = 1.5184 mm
The same 16 gauge in stainless is 2.5 ÷ 40 = 0.0625 in = 1.5875 mm
The same 16 gauge in galvanised steel is (2.5 + 0.15625) ÷ 41.82 = 0.0635 in = 1.6133 mm
The same 16 gauge in aluminium, brass or copper is 0.005 × 92^20/39 = 0.0508 in = 1.2908 mm — 25% thinner than the galvanised sheet with the same number on it

Every gauge, every family

Computed by this page from the MSG weight column and the three divisors, not copied from a thickness chart. Checked against published tables at nine steel gauges, four stainless, four aluminium and eight galvanised; every one agrees to the fourth decimal place of an inch.
Gauge	MSG weight (lb/sq ft)	Steel (mm)	Galvanised (mm)	Stainless (mm)	Aluminium, brass, copper (mm)	Thickest ÷ thinnest
3	10.00000	6.074	6.169	6.350	5.827	1.09
4	9.37500	5.694	5.789	5.953	5.189	1.15
5	8.75000	5.314	5.409	5.556	4.621	1.20
6	8.12500	4.935	5.030	5.159	4.115	1.25
7	7.50000	4.555	4.650	4.762	3.665	1.30
8	6.87500	4.176	4.271	4.366	3.264	1.34
9	6.25000	3.796	3.891	3.969	2.906	1.37
10	5.62500	3.416	3.511	3.572	2.588	1.38
11	5.00000	3.037	3.132	3.175	2.305	1.38
12	4.37500	2.657	2.752	2.778	2.053	1.35
13	3.75000	2.278	2.373	2.381	1.828	1.30
14	3.12500	1.898	1.993	1.984	1.628	1.22
15	2.81250	1.708	1.803	1.786	1.450	1.24
16	2.50000	1.518	1.613	1.587	1.291	1.25
17	2.25000	1.367	1.461	1.429	1.150	1.27
18	2.00000	1.215	1.310	1.270	1.024	1.28
19	1.75000	1.063	1.158	1.111	0.912	1.27
20	1.50000	0.911	1.006	0.952	0.812	1.24
21	1.37500	0.835	0.930	0.873	0.723	1.29
22	1.25000	0.759	0.854	0.794	0.644	1.33
23	1.12500	0.683	0.778	0.714	0.573	1.36
24	1.00000	0.607	0.702	0.635	0.511	1.38
25	0.87500	0.531	0.626	0.556	0.455	1.38
26	0.75000	0.456	0.550	0.476	0.405	1.36
27	0.68750	0.418	0.512	0.437	0.361	1.42
28	0.62500	0.380	0.475	0.397	0.321	1.48
29	0.56250	0.342	0.437	0.357	0.286	1.53
30	0.50000	0.304	0.399	0.318	0.255	1.57
31	0.43750	0.266	0.361	0.278	0.227	1.59
32	0.40625	0.247	0.342	0.258	0.202	1.69
33	0.37500	0.228	0.323	0.238	0.180	1.79
34	0.34375	0.209	0.304	0.218	0.160	1.90
35	0.31250	0.190	0.285	0.198	0.143	2.00
36	0.28125	0.171	0.266	0.179	0.127	2.09
37	0.26563	0.161	0.256	0.169	0.113	2.27
38	0.25000	0.152	0.247	0.159	0.101	2.45

One number, four thicknesses

At 16 gauge the spread between the thickest and the thinnest reading is 0.3 mm, which is a fifth of the sheet. At 22 gauge it is a quarter of the sheet. Anyone who assumes one table gets it wrong.
Gauge	Steel (mm)	Galvanised (mm)	Stainless (mm)	Al / brass / copper (mm)	Spread (mm)
8 gauge	4.176	4.271	4.366	3.264	1.102
10 gauge	3.416	3.511	3.572	2.588	0.984
12 gauge	2.657	2.752	2.778	2.053	0.726
14 gauge	1.898	1.993	1.984	1.628	0.365
16 gauge	1.518	1.613	1.587	1.291	0.322
18 gauge	1.215	1.310	1.270	1.024	0.286
20 gauge	0.911	1.006	0.952	0.812	0.194
22 gauge	0.759	0.854	0.794	0.644	0.210
24 gauge	0.607	0.702	0.635	0.511	0.192
26 gauge	0.456	0.550	0.476	0.405	0.146

Which scale belongs to which metal

Seven metals, five different scales, and one of them numbered backwards. The only safe habit is to write the metal and the scale next to the number, or better, to write the thickness.
Metal	Gauge scale	Specification	Note
Steel sheet, uncoated	Manufacturers’ Standard Gauge (MSG)	ASTM A568	Weight ÷ 41.82; the basis density of 501.84 lb/ft³ is about 2% above real steel
Galvanised steel	MSG plus a coating allowance	ASTM A653 / A924	The traditional table adds 0.15625 lb/ft²; a modern G90 coating is only about 0.0015 in
Stainless steel	Stainless Steel Gauge (SSG)	ASTM A240	The same weights over a 40 lb/ft²/in divisor, so 4.6% thicker than steel at every gauge
Aluminium	Brown & Sharpe, which is AWG	ASTM B209	A geometric progression, not a weight table
Brass	Brown & Sharpe	ASTM B36	Same thicknesses as aluminium, very different weights
Copper	Brown & Sharpe	ASTM B152	Usually specified by weight in oz/ft² instead
Zinc	Its own scale, running the other way	Not converted here	A HIGHER zinc gauge number means a THICKER sheet. The direction is documented; the values could not be sourced, so this page gives none rather than inventing them

Why 16 gauge is four different thicknesses

A sheet-metal gauge number is not a thickness and never was. The Manufacturers’ Standard Gauge, the scale behind steel sheet in North America, is a table of weights per square foot: 16 gauge means two and a half pounds per square foot, 18 gauge means two pounds, 24 gauge means one pound. To get from a weight to a thickness you divide by the weight of a square foot of the metal one inch thick — and that figure depends on the metal. That is the whole explanation for the thing that trips everyone up.

The four families. For uncoated steel the divisor is 41.82 pounds per square foot per inch, a density of 501.84 lb/ft³, so 16 gauge is 0.0598 in or 1.518 mm. The stainless table uses 40 instead, a density of 480 lb/ft³, which makes every stainless gauge exactly 4.6% thicker than the steel one: 16 gauge stainless is 0.0625 in, a clean one sixteenth of an inch. Galvanised sheet adds the zinc coating to the weight before dividing, traditionally 0.15625 lb/ft², so 16 gauge galvanised is 0.0635 in. And aluminium, brass and copper are not on a weight table at all — they use Brown & Sharpe, which is numerically the same scale as American Wire Gauge, a pure geometric progression, and 16 gauge there is 0.0508 in or 1.291 mm. Thickest to thinnest, the number 16 spans 0.3 mm, which is a fifth of the sheet.

Galvanised has a second complication. The traditional galvanised gauge table assumes a heavy coating by modern standards — 0.15625 lb of zinc per square foot, about 0.0037 in of thickness. Sheet bought today to ASTM A653 with a G90 coating carries 0.90 oz/ft², around 0.0015 in. So a caliper on a modern 16 gauge G90 sheet reads nearer 0.0613 in than the 0.0635 in the chart promises, and that is not a defect. This page gives both figures rather than pretending the difference does not exist.

Zinc is refused, deliberately. Zinc sheet has its own gauge scale and it runs the opposite way: a higher zinc gauge number is a thicker sheet. That direction is documented in the sources below. The values are not — not in anything that could be checked against a second publisher — so this page gives no zinc thicknesses at all. Inventing a column would be worse than leaving it out, because a wrong number is used and a missing one is looked up.

Practical advice, briefly. Write the thickness on the drawing, in millimetres, and put the gauge number in brackets if the shop wants it. If you must work in gauge, say the metal and the scale in the same breath. When you are measuring rather than ordering, measure away from the edge, take a few readings and average, and remember that mill tolerance on sheet is wide enough that a thickness often sits between two gauges. For wire rather than sheet — where the same number means three different things again — see the wire gauge converter. This page does the arithmetic. Where the answer carries a consequence — a dose, a structural load, a legal area, a medical measure — confirm it against the authority that governs it before relying on it.

Frequently asked questions

How thick is 16 gauge steel?

0.0598 in or 1.518 mm if it is uncoated steel; 0.0635 in or 1.613 mm on the traditional galvanised table; 0.0625 in or 1.588 mm in stainless; and 0.0508 in or 1.291 mm in aluminium, brass or copper. The number alone does not specify a thickness.

Why is stainless thicker than steel at the same gauge?

Because the gauge is a weight per square foot and the stainless table divides by 40 lb/ft² per inch where the steel table divides by 41.82. That makes every stainless gauge 4.6% thicker.

Is a higher gauge number thicker or thinner?

Thinner, in every scale on this page. Zinc sheet is the exception — its own scale runs the other way, a higher number meaning a thicker sheet — which is one more reason to write the thickness instead.

Why does my galvanised sheet measure thinner than the chart?

Because the traditional galvanised gauge table assumes about 0.0037 in of zinc and a modern G90 coating to ASTM A653 is only about 0.0015 in. The base steel is the same; there is less zinc on it.

Is aluminium gauge the same as steel gauge?

No. Aluminium, brass and copper use the Brown & Sharpe scale, which is numerically identical to AWG and is a geometric progression rather than a weight table. Aluminium is thinner than steel at every gauge number.

Why does this page not give zinc thicknesses?

Because they could not be sourced to a publisher that could be checked against a second one. The direction of the zinc scale is documented and is stated on the page; the values are not, and inventing them would be worse than leaving them out.

What weighs more, 16 gauge copper or 16 gauge aluminium?

Copper, by a factor of about 3.3, even though the two sheets are the same thickness — they are on the same Brown & Sharpe scale, and only the density differs.

Related calculators

References

ASTM A568/A568M, general requirements for carbon and high-strength low-alloy steel sheet. The Manufacturers’ Standard Gauge is a table of WEIGHTS per square foot, not of thicknesses; the steel basis is 41.82 lb/ft² per inch of thickness, which is a density of 501.84 lb/ft³.
ASTM A653/A653M and ASTM A924/A924M, zinc-coated (galvanized) steel sheet by the hot-dip process and its general requirements, including the coating designations G40 to G210 — G90 being 0.90 oz/ft² of zinc across both surfaces combined, about 0.0015 in of extra thickness in total.
ASTM A240/A240M (stainless sheet and plate), B209 (aluminium sheet), B152 (copper sheet) and B36 (brass sheet) — the specifications the stainless and Brown & Sharpe gauge tables belong to.
CustomPartNet, Sheet metal gauge sizes, custompartnet.com (read 26 September 2026): the Manufacturers’ Standard Gauge covers standard, galvanised and stainless steel; Brown & Sharpe, which is AWG, covers aluminium and brass; and the zinc scale runs the other way, a higher number meaning a thicker sheet. Its steel column is the check used for gauges 3, 10, 11, 20, 21, 30, 31 and 38.
Superior Steel Supply, Steel gauge chart, superiorsteelsupply.us (read 26 September 2026): the 41.82 lb/ft² per inch basis, and a galvanised weight column that is the uncoated weight plus 0.15625 lb/ft² at every gauge checked — which is what makes the galvanised thickness derivable rather than remembered.
Fabworks, What is sheet metal gauge, fabworks.com (read 26 September 2026): stainless 10, 14 and 18 gauge at 0.1406, 0.0781 and 0.0500 in and aluminium at 0.1019, 0.0641 and 0.0403 in — the independent check on the two non-steel divisors used here.
SheetGauge, Sheet metal gauge chart and Galvanized steel gauge chart, sheetguage.info (read 26 September 2026), naming ASTM A568 for MSG, A653/A924 for the coating classes and A240 for the stainless table, and giving the modern G90 allowance of about 0.0015 in against the 0.0037 in the traditional galvanised gauge table assumes.
ASTM B258, Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors. ASTM International. AWG is a formula, not a table: 36 AWG is 0.005 in and 4/0 is 0.460 in with 39 geometric steps between them.