How thick is 20 gauge aluminium?

20 gauge aluminium is 0.0320 in thick, which is 0.812 mm.

What is 20 gauge aluminium in mm?

0.812 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 20 gauge aluminium thicker than 19 gauge?

No — a lower gauge number is thicker sheet. 19 gauge aluminium is 0.0359 in (0.912 mm) against 0.0320 in (0.812 mm) for 20 gauge aluminium, a difference of 0.0039 in.

Why is 20 gauge a different thickness in other materials?

Because each material is indexed on its own gauge system. At 20 gauge: Aluminium 0.0320 in (B&S), Galvanized 0.0396 in (galvanized-MSG), Steel 0.0359 in (MSG), US Standard 0.0375 in (USG). The number is a position in a series, not a thickness, so 3 other readings of "20 gauge" are all equally correct.

Sheet metal · Sheet Aluminium · B&S

20 Gauge Aluminium Thickness in Inches and Millimetres

https://shopmath.org/gauges/aluminum/20 · data verified August 1, 2026

20 gauge aluminium sheet is 0.0320 in thick — 0.812 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: 20 ga
Material: Sheet Aluminium
Inch: 0.0320
mm: 0.812
System: B&S

20 Gauge Aluminium · nominal thickness

0.0320 in

Millimetre: 0.812mm

Nominal thickness on the B&S system. Gauge numbers are material-specific — "20 gauge" on its own does not name a thickness.

20 Gauge Aluminium Sheet Thickness

20 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.

20 Gauge Aluminium — thickness and weight
Property	Value
Thickness, decimal inch	0.0320 in
Thickness, millimetre	0.812 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.

20 Gauge Thickness in Every Other Sheet Material

Gauge 20 spans 0.0320 in to 0.0396 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 20 gauge sheet across materials
Property	Property	Thickness
Material	Gauge system	in	mm
Sheet Aluminium	B&S	0.0320	0.812
Galvanized Steel	galvanized-MSG	0.0396	1.006
Sheet Steel	MSG	0.0359	0.911
U.S. Standard Gauge	USG	0.0375	0.953

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 20 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 20 gauge
Property	Thickness
Gauge	in	mm
18 ga	0.0403	1.024
19 ga	0.0359	0.912
20 ga	0.0320	0.812
21 ga	0.0285	0.723
22 ga	0.0253	0.644

Sources and Method for 20 Gauge Aluminium Thickness

20 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 20 Gauge Aluminium Reference

Citation

ShopMath. "20 Gauge Aluminium Thickness in Inches and Millimetres." ShopMath, verified August 1, 2026, https://shopmath.org/gauges/aluminum/20

BibTeX

@misc{shopmath-gauges-aluminum-20,
  title        = {20 Gauge Aluminium Thickness in Inches and Millimetres},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/gauges/aluminum/20}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/gauges/aluminum/20

Common Questions About 20 Gauge Aluminium

How thick is 20 gauge aluminium?: 20 gauge aluminium is 0.0320 in thick, which is 0.812 mm.
What is 20 gauge aluminium in mm?: 0.812 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 20 gauge aluminium thicker than 19 gauge?: No — a lower gauge number is thicker sheet. 19 gauge aluminium is 0.0359 in (0.912 mm) against 0.0320 in (0.812 mm) for 20 gauge aluminium, a difference of 0.0039 in.
Why is 20 gauge a different thickness in other materials?: Because each material is indexed on its own gauge system. At 20 gauge: Aluminium 0.0320 in (B&S), Galvanized 0.0396 in (galvanized-MSG), Steel 0.0359 in (MSG), US Standard 0.0375 in (USG). The number is a position in a series, not a thickness, so 3 other readings of "20 gauge" are all equally correct.

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