Zinc coating mass is the single biggest driver of galvanized coil price after the base steel itself. Z180 and Z275 are the two most quoted classes under EN 10346, and choosing between them changes both your landed cost and how long the steel survives in service. Here is the practical comparison we walk buyers through before every order.
Z180 vs Z275 at a Glance
| Parameter | Z180 | Z275 |
|---|---|---|
| Total zinc, both sides | 180 g/m² | 275 g/m² |
| Approx. thickness per side | ~13 μm | ~20 μm |
| ASTM A653 equivalent | G60 | G90 |
| Typical unpainted outdoor life (C3) | 10-15 years | 20-30 years |
| Relative price | Base | +USD 15-25/ton (zinc-price dependent) |
| Typical uses | Indoor framing, ductwork, panels that will be painted | Outdoor roofing, coastal projects, unpainted structures |
When Z180 Is Enough
If the steel lives indoors, in a dry inland climate, or gets a paint or PPGI-style coating on top, Z180 is usually the economical and correct choice. Purlins inside a warehouse, HVAC ducting and steel furniture rarely justify the heavier class.
When to Pay for Z275
Specify Z275 when the surface stays bare and exposed: unpainted roofing and cladding, coastal or high-humidity sites, agricultural buildings with ammonia exposure, and any project where the consultant writes G90 into the specification. The 15-25 USD/ton premium is cheap insurance against replacing a roof ten years early.
Standards Note
Z classes are defined in EN 10346 as minimum triple-spot coating mass, both sides combined. Our mill certificates state the measured coating for every coil; third-party SGS/BV verification is available. See the full range on our galvanized steel coil page and the dedicated Z275 galvanized steel guide.
FAQ
Is Z275 the same as G90?
Effectively yes. Z275 (275 g/m² total) and ASTM A653 G90 (0.90 oz/ft²) are the customary equivalents and are accepted interchangeably in most import specifications.
Which zinc class sits under PPGI coil?
Prepainted coil normally uses lighter substrates (Z60-Z180) because the paint system carries most of the corrosion protection. See our PPGI coil specifications.
How do I calculate coil weight for each class?
Use our free steel coil calculator — coating class changes total mass slightly on thin gauges.
Do you stock both classes?
Yes. Z40 through Z275 are regular production, MOQ 25 tons per size, shipping FOB Tianjin (Xingang).
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