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

https://shopmath.org/gauges/us-standard/30 · data verified August 1, 2026

30 gauge U.S. Standard sheet is 0.0125 in thick — 0.318 mm. A square foot weighs 0.50 lb (2.44 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
30 ga
Material
U.S. Standard Gauge
Inch
0.0125
mm
0.318
System
USG

30 Gauge U.S. Standard · nominal thickness

0.0125 in

Millimetre
0.318mm
Weight
0.50lb/ft²
Weight
2.44kg/m²

Nominal thickness on the USG system. Gauge numbers are material-specific — "30 gauge" on its own does not name a thickness.

30 Gauge U.S. Standard Sheet Thickness

30 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.

30 Gauge U.S. Standard — thickness and weight
PropertyValue
Thickness, decimal inch0.0125 in
Thickness, millimetre0.318 mm
Weight per square foot0.50 lb/ft²
Weight per square metre2.44 kg/m²
Gauge systemUSG

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.

30 Gauge Thickness in Every Other Sheet Material

Gauge 30 spans 0.0100 in to 0.0157 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 30 gauge sheet across materials
PropertyPropertyThickness
MaterialGauge systeminmm
Sheet AluminiumB&S0.01000.255
Galvanized Steelgalvanized-MSG0.01570.399
Sheet SteelMSG0.01200.304
U.S. Standard GaugeUSG0.01250.318

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 30 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 30 gauge
PropertyThickness
Gaugeinmm
28 ga0.01560.397
29 ga0.01410.357
30 ga0.01250.318
31 ga0.01090.278
32 ga0.01020.258

Sources and Method for 30 Gauge U.S. Standard Thickness

30 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

  0.0125 × 41.82  =  0.50 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 30 Gauge U.S. Standard Reference

Citation

ShopMath. "30 Gauge U.S. Standard Thickness in Inches and Millimetres." ShopMath, verified August 1, 2026, https://shopmath.org/gauges/us-standard/30

BibTeX

@misc{shopmath-gauges-us-standard-30,
  title        = {30 Gauge U.S. Standard Thickness in Inches and Millimetres},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/gauges/us-standard/30}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/gauges/us-standard/30

Common Questions About 30 Gauge U.S. Standard

How thick is 30 gauge U.S. Standard?

30 gauge U.S. Standard is 0.0125 in thick, which is 0.318 mm. A square foot weighs 0.50 lb (2.44 kg/m²).

What is 30 gauge U.S. Standard in mm?

0.318 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 30 gauge U.S. Standard thicker than 29 gauge?

No — a lower gauge number is thicker sheet. 29 gauge us standard is 0.0141 in (0.357 mm) against 0.0125 in (0.318 mm) for 30 gauge U.S. Standard, a difference of 0.0016 in.

Why is 30 gauge a different thickness in other materials?

Because each material is indexed on its own gauge system. At 30 gauge: Aluminium 0.0100 in (B&S), Galvanized 0.0157 in (galvanized-MSG), Steel 0.0120 in (MSG), US Standard 0.0125 in (USG). The number is a position in a series, not a thickness, so 3 other readings of "30 gauge" are all equally correct.

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