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Galvanized Steel Weight: Z40 to Z275 Coating Thickness Explained
Galvanized Steel Weight: Z40 to Z275 Coating Thickness Explained
When you buy galvanized steel sheet or coil, the coating mass grade — Z40, Z80, Z120, Z180, Z275 — determines how long the zinc layer lasts and how much the final product weighs. This guide decodes the Z-number system, compares common grades, and shows how coating mass affects price, weight and service life.
What Does Z275 Actually Mean
The number after Z is the total zinc coating mass on both sides of the sheet, measured in grams per square metre. Z275 means 275 g/m² total zinc, or about 137.5 گرم بر متر مربع در هر طرف. Converting to thickness: zinc density is 7.14 g/cm³, so 275 g/m² equals roughly 38.5 میکرومتر کل, or about 19 میکرومتر در هر طرف. This is the most common grade for outdoor structural steel, fencing and roofing. ما را ببینید hot-dip galvanized steel tube.
| درجه | Total g/m² | Per-side µm | استفاده معمولی |
|---|---|---|---|
| Z40 | 40 | ~2.8 | سرپوشیده, appliance backs |
| Z80 | 80 | ~5.6 | Light indoor, قاب ها |
| Z120 | 120 | ~8.4 | عمومی داخلی, dry outdoor |
| Z180 | 180 | ~12.6 | Outdoor moderate, شمشیربازی |
| Z275 | 275 | ~19.3 | سازه در فضای باز, سقف سازی |
| Z350 | 350 | ~24.5 | ساحلی, severe corrosion |
How Coating Mass Affects Weight and Price
Zinc adds weight. الف 1 mm thick steel sheet at Z275 carries about 2.2 kg/m² of steel plus 0.275 kg/m² of zinc, در مورد 12 % extra weight compared to uncoated cold-rolled sheet. When comparing quotes, always confirm whether the price is per tonne of steel or per tonne of coated product — a Z275 coil weighs more than a Z80 coil of the same dimensions, and a per-tonne price that looks cheaper may actually cost more per usable square metre.
Service Life by Environment
In rural, dry air, Z120 lasts 20+ سال. In urban or coastal air, Z275 is the minimum — a Z120 sheet will start rusting at cut edges within 5 سال, while Z275 lasts 15 – 25 سال. In coastal or industrial environments with salt spray, specify Z350 or hot-dip galvanized after fabrication. For pre-painted (PPGI) applications, the coating is usually Z100 – Z180 because the paint layer provides the primary barrier.
