Sheet metal · Galvanized Steel · galvanized-MSG
18 Gauge Galvanised Steel Thickness in Inches and Millimetres
https://shopmath.org/gauges/galvanized/18 · data verified August 1, 2026
18 gauge galvanised steel sheet is 0.0516 in thick — 1.310 mm. A square foot weighs 2.00 lb (9.77 kg/m²). The gauge number indexes the galvanized-MSG system, so the same number is a different thickness in another material — the comparison is below. Thicknesses are nominal, before mill tolerance.
- Gauge
- 18 ga
- Material
- Galvanized Steel
- Inch
- 0.0516
- mm
- 1.310
- System
- galvanized-MSG
18 Gauge Galvanised Steel · nominal thickness
0.0516 in
- Millimetre
- 1.310mm
- Weight
- 2.00lb/ft²
- Weight
- 9.77kg/m²
Nominal thickness on the galvanized-MSG system. Gauge numbers are material-specific — "18 gauge" on its own does not name a thickness.
18 Gauge Galvanised Steel Sheet Thickness
18 Gauge Galvanised Steel is defined by the MSG plus zinc coating allowance, 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.
| Property | Value |
|---|---|
| Thickness, decimal inch | 0.0516 in |
| Thickness, millimetre | 1.310 mm |
| Weight per square foot | 2.00 lb/ft² |
| Weight per square metre | 9.77 kg/m² |
| Gauge system | galvanized-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.
18 Gauge Thickness in Every Other Sheet Material
Gauge 18 spans 0.0403 in to 0.0516 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.
| Property | Property | Thickness | |
|---|---|---|---|
| Material | Gauge system | in | mm |
| Sheet Aluminium | B&S | 0.0403 | 1.024 |
| Galvanized Steel | galvanized-MSG | 0.0516 | 1.310 |
| Sheet Steel | MSG | 0.0478 | 1.215 |
| U.S. Standard Gauge | USG | 0.0500 | 1.270 |
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 18 Gauge Galvanised 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.
Sources and Method for 18 Gauge Galvanised Steel Thickness
- 18 Gauge Galvanised 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 0.0516 × 41.82 = 2.00 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 to Cite This 18 Gauge Galvanised Steel Reference
Citation
ShopMath. "18 Gauge Galvanised Steel Thickness in Inches and Millimetres." ShopMath, verified August 1, 2026, https://shopmath.org/gauges/galvanized/18
BibTeX
@misc{shopmath-gauges-galvanized-18,
title = {18 Gauge Galvanised Steel Thickness in Inches and Millimetres},
author = {{ShopMath}},
year = {2026},
howpublished = {\url{https://shopmath.org/gauges/galvanized/18}},
note = {Data verified 2026-08-01}
}Permanent URL
https://shopmath.org/gauges/galvanized/18
Common Questions About 18 Gauge Galvanised Steel
How thick is 18 gauge galvanised steel?
- 18 gauge galvanised steel is 0.0516 in thick, which is 1.310 mm. A square foot weighs 2.00 lb (9.77 kg/m²).
What is 18 gauge galvanised steel in mm?
- 1.310 mm. The gauge number is an index into the galvanized-MSG system rather than a measurement, so it converts to a fixed thickness rather than a round metric figure.
Is 18 gauge galvanised steel thicker than 17 gauge?
- No — a lower gauge number is thicker sheet. 17 gauge galvanized is 0.0575 in (1.462 mm) against 0.0516 in (1.310 mm) for 18 gauge galvanised steel, a difference of 0.0059 in.
Why is 18 gauge a different thickness in other materials?
- Because each material is indexed on its own gauge system. At 18 gauge: Aluminium 0.0403 in (B&S), Galvanized 0.0516 in (galvanized-MSG), Steel 0.0478 in (MSG), US Standard 0.0500 in (USG). The number is a position in a series, not a thickness, so 3 other readings of "18 gauge" are all equally correct.
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