Sheet Metal Gauge Converter
Convert sheet metal gauge numbers to inches and millimeters for steel, aluminum, galvanized steel, and stainless steel.
Find thickness, weight per square foot, and equivalent wire gauge.
What Is Sheet Metal Gauge? Gauge is a traditional unit for sheet metal thickness — a higher gauge number means thinner metal. The gauge system originated in the wire drawing trade in England and was later applied to sheet metal. Different gauge standards exist for different materials — steel, aluminum, and galvanized steel all use different gauge-to-thickness conversions. This is a major source of confusion: 18 gauge stainless steel is NOT the same thickness as 18 gauge aluminum.
Common Gauge Standards US Standard Gauge (USS): used for steel and galvanized steel. Manufacturer’s Standard Gauge (MSG): used for steel strip and sheet. American Wire Gauge (AWG) / Brown & Sharpe Gauge: for non-ferrous metals (aluminum, copper, brass). Birmingham Wire Gauge (BWG): for wire and tubing — different again.
Why Does Gauge Run Backwards? In wire drawing, metal is pulled through progressively smaller dies — each pass is one “gauge.” More passes = thinner wire = higher gauge number. For sheet metal, the same convention was applied: thicker sheets had lower gauge numbers. This counterintuitive system persists because of industry tradition.
Approximate USS Gauge to Thickness (Steel) 7 gauge: 0.1793" (4.55 mm). 10 gauge: 0.1345" (3.42 mm). 12 gauge: 0.1046" (2.66 mm). 14 gauge: 0.0747" (1.90 mm). 16 gauge: 0.0598" (1.52 mm). 18 gauge: 0.0478" (1.21 mm). 20 gauge: 0.0359" (0.91 mm). 22 gauge: 0.0299" (0.76 mm). 24 gauge: 0.0239" (0.61 mm). 26 gauge: 0.0179" (0.45 mm). 28 gauge: 0.0149" (0.38 mm).
Common Applications by Gauge 3–7 gauge: heavy structural steel, armor plating, heavy machinery. 10–12 gauge: truck bodies, farm equipment, heavy ductwork. 14–16 gauge: HVAC ductwork, appliance frames, auto body panels. 18–20 gauge: light ductwork, enclosures, light auto body. 22–26 gauge: roofing panels, light HVAC, electronics enclosures. 28–30 gauge: foil, very thin sheet for art and light fabrication.
Weight Considerations Steel: 0.2904 lb/in³ (7.85 g/cm³). Aluminum: 0.0975 lb/in³ (2.70 g/cm³). Weight per sq ft = thickness (in) × 144 × density (lb/in³). 16 gauge steel sheet: ~2.5 lb/sq ft. 16 gauge aluminum: ~0.84 lb/sq ft. Weight is critical for shipping costs, structural loads, and handling equipment ratings.
HVAC Ductwork Standards SMACNA (Sheet Metal and Air Conditioning Contractors’ National Association) specifies gauge by duct size and pressure class. Round duct up to 12": 26 gauge for low pressure, 24 gauge for medium, 22 gauge for high. Rectangular duct up to 12" dimension: 26 gauge for low pressure. Heavier gauge for fittings, elbows, and high-velocity systems.