How thick is 31 gauge aluminium?

31 gauge aluminium is 0.0089 in thick, which is 0.227 mm.

What is 31 gauge aluminium in mm?

0.227 mm. The gauge number is an index into the B&S system rather than a measurement, so it converts to a fixed thickness rather than a round metric figure.

Is 31 gauge aluminium thicker than 30 gauge?

No — a lower gauge number is thicker sheet. 30 gauge aluminium is 0.0100 in (0.255 mm) against 0.0089 in (0.227 mm) for 31 gauge aluminium, a difference of 0.0011 in.

Why is 31 gauge a different thickness in other materials?

Because each material is indexed on its own gauge system. At 31 gauge: Aluminium 0.0089 in (B&S), Galvanized 0.0142 in (galvanized-MSG), Steel 0.0105 in (MSG), US Standard 0.0109 in (USG). The number is a position in a series, not a thickness, so 3 other readings of "31 gauge" are all equally correct.

Sheet metal · Sheet Aluminium · B&S

31 Gauge Aluminium Thickness in Inches and Millimetres

https://shopmath.org/gauges/aluminum/31 · data verified August 1, 2026

31 gauge aluminium sheet is 0.0089 in thick — 0.227 mm. The gauge number indexes the B&S system, so the same number is a different thickness in another material — the comparison is below. Thicknesses are nominal, before mill tolerance.

Gauge: 31 ga
Material: Sheet Aluminium
Inch: 0.0089
mm: 0.227
System: B&S

31 Gauge Aluminium · nominal thickness

0.0089 in

Millimetre: 0.227mm

Nominal thickness on the B&S system. Gauge numbers are material-specific — "31 gauge" on its own does not name a thickness.

31 Gauge Aluminium Sheet Thickness

31 Gauge Aluminium is defined by the Brown & Sharpe (AWG), not by a measurement — the gauge number is an index into that system, which is why the same number means a different thickness in another material.

31 Gauge Aluminium — thickness and weight
Property	Value
Thickness, decimal inch	0.0089 in
Thickness, millimetre	0.227 mm
Gauge system	B&S

Nominal thickness. Mill tolerance on sheet is typically a few thousandths of an inch either way and varies with width and process; measure the stock when the fit matters.

31 Gauge Thickness in Every Other Sheet Material

Gauge 31 spans 0.0089 in to 0.0142 in depending on the material, because each material is indexed on a different gauge system. Ordering sheet by gauge without naming the material is how the wrong thickness arrives.

Thickness of 31 gauge sheet across materials
Property	Property	Thickness
Material	Gauge system	in	mm
Sheet Aluminium	B&S	0.0089	0.227
Galvanized Steel	galvanized-MSG	0.0142	0.361
Sheet Steel	MSG	0.0105	0.266
U.S. Standard Gauge	USG	0.0109	0.278

Steel uses the Manufacturers' Standard Gauge, galvanised adds a zinc-coating allowance to the steel thickness, aluminium and other non-ferrous sheet use the Brown & Sharpe geometric series, and U.S. Standard is the 1893 statute on a wrought-iron basis.

Gauges Either Side of 31 Gauge Aluminium

A higher gauge number is thinner sheet. The steps are not equal — the gauge systems are geometric, so the difference between two gauges shrinks as the sheet gets thinner.

Sheet Aluminium gauges adjacent to 31 gauge
Property	Thickness
Gauge	in	mm
29 ga	0.0113	0.286
30 ga	0.0100	0.255
31 ga	0.0089	0.227
32 ga	0.0080	0.202
33 ga	0.0071	0.180

Sources and Method for 31 Gauge Aluminium Thickness

31 Gauge Aluminium thicknesscomputed

15 U.S.C. 206 (Act of Mar. 3, 1893, ch. 221, 27 Stat. 746) — U.S. Standard Gauge for sheet and plate iron and steel; 15 U.S.C. 206 statutory weights; MSG (41.82 lb/ft2 per inch), galvanized zinc allowance, and Brown & Sharpe formula per docs/research/data-sourcing.md §3.7

Verified against Wikipedia Sheet metal, Standard sheet metal gauges table (CC BY-SA 4.0) — 137/137 checks passed at 0.05 mil

Computed from the standard's formulas, then checked against published tables.

Assumptions

Thicknesses are nominal. Mill tolerance varies with width, process and material and is not part of the gauge definition.
Gauge is an index into a material-specific system, not a unit. A gauge number without a material is ambiguous by construction.
Dataset scope: EXCLUDED: stainless steel (genuinely ambiguous convention, only one source in hand), zinc, copper, brass, steel tube wall.

Data last verified

August 1, 2026

How this data is built and checked →

How to Cite This 31 Gauge Aluminium Reference

Citation

ShopMath. "31 Gauge Aluminium Thickness in Inches and Millimetres." ShopMath, verified August 1, 2026, https://shopmath.org/gauges/aluminum/31

BibTeX

@misc{shopmath-gauges-aluminum-31,
  title        = {31 Gauge Aluminium Thickness in Inches and Millimetres},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/gauges/aluminum/31}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/gauges/aluminum/31

Common Questions About 31 Gauge Aluminium

How thick is 31 gauge aluminium?: 31 gauge aluminium is 0.0089 in thick, which is 0.227 mm.
What is 31 gauge aluminium in mm?: 0.227 mm. The gauge number is an index into the B&S system rather than a measurement, so it converts to a fixed thickness rather than a round metric figure.
Is 31 gauge aluminium thicker than 30 gauge?: No — a lower gauge number is thicker sheet. 30 gauge aluminium is 0.0100 in (0.255 mm) against 0.0089 in (0.227 mm) for 31 gauge aluminium, a difference of 0.0011 in.
Why is 31 gauge a different thickness in other materials?: Because each material is indexed on its own gauge system. At 31 gauge: Aluminium 0.0089 in (B&S), Galvanized 0.0142 in (galvanized-MSG), Steel 0.0105 in (MSG), US Standard 0.0109 in (USG). The number is a position in a series, not a thickness, so 3 other readings of "31 gauge" are all equally correct.

All 33 aluminium gauges · Sheet metal gauge chart · Every gauge system