How thick is 9 gauge U.S. Standard?

9 gauge U.S. Standard is 0.1563 in thick, which is 3.969 mm. A square foot weighs 6.25 lb (30.52 kg/m²).

What is 9 gauge U.S. Standard in mm?

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

Is 9 gauge U.S. Standard thicker than 8 gauge?

No — a lower gauge number is thicker sheet. 8 gauge us standard is 0.1719 in (4.366 mm) against 0.1563 in (3.969 mm) for 9 gauge U.S. Standard, a difference of 0.0156 in.

Why is 9 gauge a different thickness in other materials?

Because each material is indexed on its own gauge system. At 9 gauge: Aluminium 0.1144 in (B&S), Galvanized 0.1532 in (galvanized-MSG), Steel 0.1495 in (MSG), US Standard 0.1563 in (USG). The number is a position in a series, not a thickness, so 3 other readings of "9 gauge" are all equally correct.

Sheet metal · U.S. Standard Gauge · USG

9 Gauge U.S. Standard Thickness in Inches and Millimetres

https://shopmath.org/gauges/us-standard/9 · data verified August 1, 2026

9 gauge U.S. Standard sheet is 0.1563 in thick — 3.969 mm. A square foot weighs 6.25 lb (30.52 kg/m²). The gauge number indexes the USG system, so the same number is a different thickness in another material — the comparison is below. Thicknesses are nominal, before mill tolerance.

Gauge: 9 ga
Material: U.S. Standard Gauge
Inch: 0.1563
mm: 3.969
System: USG

9 Gauge U.S. Standard · nominal thickness

0.1563 in

Millimetre: 3.969mm
Weight: 6.25lb/ft²
Weight: 30.52kg/m²

Nominal thickness on the USG system. Gauge numbers are material-specific — "9 gauge" on its own does not name a thickness.

9 Gauge U.S. Standard Sheet Thickness

9 Gauge U.S. Standard is defined by the 15 U.S.C. 206 (wrought iron basis), 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.

9 Gauge U.S. Standard — thickness and weight
Property	Value
Thickness, decimal inch	0.1563 in
Thickness, millimetre	3.969 mm
Weight per square foot	6.25 lb/ft²
Weight per square metre	30.52 kg/m²
Gauge system	USG

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.

9 Gauge Thickness in Every Other Sheet Material

Gauge 9 spans 0.1144 in to 0.1563 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 9 gauge sheet across materials
Property	Property	Thickness
Material	Gauge system	in	mm
Sheet Aluminium	B&S	0.1144	2.906
Galvanized Steel	galvanized-MSG	0.1532	3.891
Sheet Steel	MSG	0.1495	3.796
U.S. Standard Gauge	USG	0.1563	3.969

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 9 Gauge U.S. Standard

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.

U.S. Standard Gauge gauges adjacent to 9 gauge
Property	Thickness
Gauge	in	mm
7 ga	0.1875	4.763
8 ga	0.1719	4.366
9 ga	0.1563	3.969
10 ga	0.1406	3.572
11 ga	0.1250	3.175

Sources and Method for 9 Gauge U.S. Standard Thickness

9 Gauge U.S. Standard 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

  0.1563 × 41.82  =  6.25 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 9 Gauge U.S. Standard Reference

Citation

ShopMath. "9 Gauge U.S. Standard Thickness in Inches and Millimetres." ShopMath, verified August 1, 2026, https://shopmath.org/gauges/us-standard/9

BibTeX

@misc{shopmath-gauges-us-standard-9,
  title        = {9 Gauge U.S. Standard Thickness in Inches and Millimetres},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/gauges/us-standard/9}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/gauges/us-standard/9

Common Questions About 9 Gauge U.S. Standard

How thick is 9 gauge U.S. Standard?: 9 gauge U.S. Standard is 0.1563 in thick, which is 3.969 mm. A square foot weighs 6.25 lb (30.52 kg/m²).
What is 9 gauge U.S. Standard in mm?: 3.969 mm. The gauge number is an index into the USG system rather than a measurement, so it converts to a fixed thickness rather than a round metric figure.
Is 9 gauge U.S. Standard thicker than 8 gauge?: No — a lower gauge number is thicker sheet. 8 gauge us standard is 0.1719 in (4.366 mm) against 0.1563 in (3.969 mm) for 9 gauge U.S. Standard, a difference of 0.0156 in.
Why is 9 gauge a different thickness in other materials?: Because each material is indexed on its own gauge system. At 9 gauge: Aluminium 0.1144 in (B&S), Galvanized 0.1532 in (galvanized-MSG), Steel 0.1495 in (MSG), US Standard 0.1563 in (USG). The number is a position in a series, not a thickness, so 3 other readings of "9 gauge" are all equally correct.

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