How thick is 4 gauge steel?

4 gauge steel is 0.2242 in thick, which is 5.694 mm. A square foot weighs 9.38 lb (45.77 kg/m²).

What is 4 gauge steel in mm?

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

Is 4 gauge steel thicker than 3 gauge?

No — a lower gauge number is thicker sheet. 3 gauge steel is 0.2391 in (6.074 mm) against 0.2242 in (5.694 mm) for 4 gauge steel, a difference of 0.0149 in.

Why is 4 gauge a different thickness in other materials?

Because each material is indexed on its own gauge system. At 4 gauge: Aluminium 0.2043 in (B&S), Steel 0.2242 in (MSG), US Standard 0.2344 in (USG). The number is a position in a series, not a thickness, so 2 other readings of "4 gauge" are all equally correct.

Sheet metal · Sheet Steel · MSG

4 Gauge Steel Thickness in Inches and Millimetres

https://shopmath.org/gauges/steel/4 · data verified August 1, 2026

4 gauge steel sheet is 0.2242 in thick — 5.694 mm. A square foot weighs 9.38 lb (45.77 kg/m²). The gauge number indexes the MSG system, so the same number is a different thickness in another material — the comparison is below. Thicknesses are nominal, before mill tolerance.

Gauge: 4 ga
Material: Sheet Steel
Inch: 0.2242
mm: 5.694
System: MSG

4 Gauge Steel · nominal thickness

0.2242 in

Millimetre: 5.694mm
Weight: 9.38lb/ft²
Weight: 45.77kg/m²

Nominal thickness on the MSG system. Gauge numbers are material-specific — "4 gauge" on its own does not name a thickness.

4 Gauge Steel Sheet Thickness

4 Gauge Steel is defined by the Manufacturers' Standard Gauge (MSG), 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.

4 Gauge Steel — thickness and weight
Property	Value
Thickness, decimal inch	0.2242 in
Thickness, millimetre	5.694 mm
Weight per square foot	9.38 lb/ft²
Weight per square metre	45.77 kg/m²
Gauge system	MSG

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.

4 Gauge Thickness in Every Other Sheet Material

Gauge 4 spans 0.2043 in to 0.2344 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 4 gauge sheet across materials
Property	Property	Thickness
Material	Gauge system	in	mm
Sheet Aluminium	B&S	0.2043	5.189
Sheet Steel	MSG	0.2242	5.694
U.S. Standard Gauge	USG	0.2344	5.953

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 4 Gauge Steel

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 Steel gauges adjacent to 4 gauge
Property	Thickness
Gauge	in	mm
3 ga	0.2391	6.074
4 ga	0.2242	5.694
5 ga	0.2092	5.314
6 ga	0.1943	4.935

Sources and Method for 4 Gauge Steel Thickness

4 Gauge Steel 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.

Formula

Weight per square foot, sheet steel

lb/ft²  =  thickness (in) × 41.82

  0.2242 × 41.82  =  9.38 lb/ft²

41.82 lb/ft² per inch of thickness is the Manufacturers' Standard Gauge basis for steel. The U.S. Standard Gauge of 1893 uses a wrought-iron basis of 40 lb/ft² per inch, which is why the two systems differ.

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 4 Gauge Steel Reference

Citation

ShopMath. "4 Gauge Steel Thickness in Inches and Millimetres." ShopMath, verified August 1, 2026, https://shopmath.org/gauges/steel/4

BibTeX

@misc{shopmath-gauges-steel-4,
  title        = {4 Gauge Steel Thickness in Inches and Millimetres},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/gauges/steel/4}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/gauges/steel/4

Common Questions About 4 Gauge Steel

How thick is 4 gauge steel?: 4 gauge steel is 0.2242 in thick, which is 5.694 mm. A square foot weighs 9.38 lb (45.77 kg/m²).
What is 4 gauge steel in mm?: 5.694 mm. The gauge number is an index into the MSG system rather than a measurement, so it converts to a fixed thickness rather than a round metric figure.
Is 4 gauge steel thicker than 3 gauge?: No — a lower gauge number is thicker sheet. 3 gauge steel is 0.2391 in (6.074 mm) against 0.2242 in (5.694 mm) for 4 gauge steel, a difference of 0.0149 in.
Why is 4 gauge a different thickness in other materials?: Because each material is indexed on its own gauge system. At 4 gauge: Aluminium 0.2043 in (B&S), Steel 0.2242 in (MSG), US Standard 0.2344 in (USG). The number is a position in a series, not a thickness, so 2 other readings of "4 gauge" are all equally correct.

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