Why gauge numbers are confusing
A gauge number is not a measurement. It comes from old wire-drawing practice, and different industries and countries fixed different tables. 18 gauge is 1.22 mm in SWG, 1.21 mm in US standard steel, 1.27 mm in stainless and only 1.02 mm in aluminium. Higher numbers are always thinner.
Which system to use in India
Indian traders often quote GI and CR sheets in SWG (Standard Wire Gauge), but many now quote directly in mm (for example 0.50 mm or 1.2 mm). Imported sheets and drawings from the US use the US tables. When ordering, always confirm the thickness in mm — and measure delivered sheets with a micrometer or vernier.
Weight per square metre
kg per m² = thickness (mm) × density (g/cm³)
So 1.2 mm mild steel weighs 1.2 × 7.85 = 9.42 kg/m². A standard 8 × 4 ft sheet (2.973 m²) of it weighs about 28 kg.
Questions people ask
Is 16 gauge thicker than 20 gauge?
Is GI sheet thickness quoted with or without zinc?
What is the thickness of 22 gauge GI sheet?
Sources
- BS 3737 Standard Wire Gauge (historical British standard)
- Manufacturers’ Standard Gauge for sheet steel
Results are estimates to help you plan. Always confirm important numbers with the seller, carrier or authority concerned. Last reviewed: November 2026.