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Galvanized Sheet Metal Gauge Chart

Galvanized sheet is carbon steel wearing a zinc coat, and its gauge table says so: every published galvanized thickness is the matching carbon steel gauge plus 0.0037 inches for the coating, under ASTM A653 practice. That makes galvanized the thickest reading of the four metals at almost every gauge — at 16 gauge, 0.0635 inches — and it means the zinc is inside the number you are quoted, not added afterwards.

One cell of this chart is empty on purpose. Published galvanized tables begin at 8 gauge; no 7 gauge galvanized value exists in the standard tables, so the chart shows a dash rather than an invented number. The range runs from 8 gauge at 0.1681 inches down to 30 gauge at 0.0157 inches.

Galvanized gauge thickness chart

The zinc allowance, and why it matters more as sheet gets thinner

The 0.0037 inch allowance is a fixed slice added to every gauge, but its share of the total grows as the sheet thins. At 10 gauge it is under 3 percent of the 0.1382 inch total. At 30 gauge it is 0.0037 of 0.0157 inches — about a quarter of the sheet you are holding is zinc coating and the allowance built around it. That is worth knowing when thin galvanized behaves differently from thin black steel in forming or weight estimates.

It also explains the one place the four-metal order flips. At heavy gauges stainless is thickest; at 30 gauge, galvanized (0.0157 in) is thicker than stainless (0.0125 in) and steel (0.0120 in), purely because the coating allowance does not shrink with the sheet.

Why there is no 7 gauge galvanized

The galvanized series is not an independent table — it is the steel table plus the coating rule, published only over the range manufacturers actually coat and sell as galvanized sheet. Those published tables start at 8 gauge (0.1681 in). Heavier coated work is normally specified by decimal thickness or as plate, outside the sheet gauge system altogether.

So if a quote or a drawing calls for 7 gauge galvanized, treat it as a flag: either the number came from running the steel value through the coating rule by hand — which no standard table backs — or the job wants plate specified in inches. Ask for a decimal thickness and order to that.

Where galvanized gauges get used — and the welding caution

Galvanized lives outdoors and in air handling. Ductwork is its biggest use: residential and light commercial ducts are commonly 24 to 26 gauge, moving to 22 gauge and heavier as duct size and pressure class rise. Roofing and flashing run 24 to 29 gauge. Agricultural buildings, culvert stock, and outdoor enclosures use it wherever painted steel would need constant maintenance — the zinc sacrifices itself slowly so the steel underneath does not rust.

The caution: welding galvanized sheet burns the zinc at the joint, and the fumes are a genuine health hazard. Standard shop practice is to grind the coating back an inch or so from the weld line, weld with strong ventilation or a respirator, and re-coat the joint afterwards. If a job needs a lot of welding, price it in plain steel and paint or coat after fabrication instead.

Nearest galvanized gauge for metric thicknesses

Computed from the chart above: for each common metric size, the published galvanized gauge whose thickness is closest, with its actual thickness.

Related charts

• Sheet metal gauge chart (all four metals)
• Steel gauge chart
• Stainless steel gauge chart
• Aluminum gauge chart
• Gauge to mm converter
• All charts

Thickness values follow MSG + 0.0037 in zinc allowance (ASTM A653); no gauge 7 published; cross-checked against published supplier charts, November 2026.