Sheet Metal Gauge Chart — Thickness & Weight

Gauge to decimal thickness and weight for the sheet HVAC shops actually buy: galvanized steel (the duct standard), uncoated MSG carbon steel, and B&S-gauge aluminum, from 30 through 10 gauge. Gauge is a weight convention, not a spec — the decimals here are the nominal equivalents mill orders are written around.

Galvanized steel sheet

ASTM A653 practice
Galvanized Sheet Gauge nominal decimal equivalents — the series duct gauge callouts refer to. Includes the standard 2.5 oz/ft² zinc allowance.
GaugeInchesmmlb/ft²
300.01570.400.656
290.01720.440.719
280.01870.470.781
270.02020.510.844
260.02170.550.906
250.02470.631.031
240.02760.701.156
230.03060.781.281
220.03360.851.406
210.03660.931.531
200.03961.011.656
190.04561.161.906
180.05161.312.156
170.05751.462.406
160.06351.612.656
150.07101.802.969
140.07851.993.281
130.09342.373.906
120.10842.754.531
110.12333.135.156
100.13823.515.781
Galvanized rows equal the uncoated MSG values plus the zinc: +0.0037" of thickness and +0.156 lb/ft² of weight (the 2.5 oz/ft² both-sides coating allowance).

Uncoated carbon steel sheet

Manufacturers' Std Gauge
MSG nominal decimals for cold- and hot-rolled carbon steel sheet — 41.82 lb/ft² per inch of thickness, with 24 gauge defined as exactly 1 lb/ft².
GaugeInchesmmlb/ft²
300.01200.300.500
290.01350.340.563
280.01490.380.625
270.01640.420.688
260.01790.450.750
250.02090.530.875
240.02390.611.000
230.02690.681.125
220.02990.761.250
210.03290.841.375
200.03590.911.500
190.04181.061.750
180.04781.212.000
170.05381.372.250
160.05981.522.500
150.06731.712.813
140.07471.903.125
130.08972.283.750
120.10462.664.375
110.11963.045.000
100.13453.425.625
Carbon steel uses the Manufacturers' Standard Gauge (MSG) decimals. Some circulating charts print the obsolete US Standard series (30 ga = 0.0125", 16 ga = 0.0625") — those are not the numbers steel is sold to.

Aluminum sheet

B&S gauge
Brown & Sharpe gauge decimals for aluminum sheet, even gauges — a different series again, and roughly a third the weight of steel.
GaugeInchesmmlb/ft²
300.01000.250.141
280.01260.320.178
260.01590.400.224
240.02010.510.284
220.02530.640.357
200.03200.810.452
180.04031.020.569
160.05081.290.717
140.06411.630.905
120.08082.051.140
100.10192.591.438
Stainless is deliberately absent: two irreconcilable gauge series circulate for it and no two independent sources agreed, so per the verification rule it is omitted rather than guessed.

Reading gauge like a fabricator

Gauge is a weight-based convention, not a thickness specification — mill orders under ASTM A653/A1008 are written in decimal thickness with rolling tolerances. These are the nominal decimal equivalents. Duct construction minimums are written in decimal thickness for exactly this reason — the duct gauge chart shows how the mechanical code's thicknesses map back to nominal gauges. Weight per square foot drives hanger sizing and shipping: takeoffs multiply duct surface area by the lb/ft² column, then check support spacing on the hanger spacing chart.

Common questions

How thick is 26 gauge sheet metal?

Depends on the material, because each metal has its own gauge series: 26 gauge galvanized is 0.0217" (0.55 mm), 26 gauge uncoated steel is 0.0179", and 26 gauge aluminum is 0.0159". Quoting a gauge without the material is how sheet gets mis-ordered.

Why is galvanized thickness different from plain steel at the same gauge?

The zinc. Galvanized sheet is the uncoated Manufacturers' Standard Gauge steel plus the coating allowance — 0.0037" of thickness and 0.156 lb/ft² of weight for the standard 2.5 oz/ft² both-sides coating — so every galvanized row runs exactly that much heavier and thicker than its uncoated twin.

How much does a sheet of 20 gauge steel weigh?

Uncoated 20 gauge runs 1.50 lb/ft² — a 4×8 sheet is 48 lb. Galvanized 20 gauge is 1.656 lb/ft², so the same 4×8 sheet weighs 53 lb. The MSG convention makes the math easy: steel weighs 41.82 lb/ft² per inch of thickness, and 24 gauge was defined as exactly 1 lb/ft².

Why do different gauge charts disagree?

Two reasons: some charts still print the obsolete US Standard series for steel (0.0125" for 30 gauge instead of MSG's 0.0120"), and several widely copied charts carry typos at specific gauges. This chart uses the Manufacturers' Standard Gauge decimals steel is actually sold to, cross-checked across three independent publishers — and stainless is omitted entirely because no two sources agree on its series.

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