When you see G60, G90 or G185 on galvanized sheet specs, you are looking at coating mass from ASTM A653. Higher numbers mean more zinc and—generally—longer time to red rust outdoors. If your project uses metric “Z” values, pair them like this: G60 ≈ Z180, G90 ≈ Z275, G185 ≈ Z565 (total both sides).
What the numbers mean
- Units: G = oz/ft² total both sides; Z = g/m². 1 oz/ft² ≈ 305 g/m².
- Per side thickness (rule of thumb): Z180 ≈ 25 μm total (~12 μm/side); Z275 ≈ 38 μm total (~19 μm/side); Z565 ≈ 79 μm total (~40 μm/side).
- Distribution: Mass is two-side total; one side may be slightly heavier. If you need a minimum per side, say so.
Where each class fits
- G60 (Z180): Interior framing, HVAC, sheltered cladding; paint extends life.
- G90 (Z275): Common default for roofs/walls in non-marine sites.
- G185 (Z565): Coastal spray, treated timber contact, exposed edges/hardware.
Coatings, paint and appearance
- Spangle: Cosmetic; performance comes from coating mass.
- Passivation/oil: Chromate-free passivation + light oil control storage stain; confirm paintability.
- Pre-painted: Polyester/SMP economical; PVDF best under strong UV/coastal.
Fabrication notes
- Cut edges: Bare after cutting—seal with zinc-rich paint in harsh sites.
- Welding: Clean to bright metal; re-coat welds if outdoors.
- Fasteners: Compatible coatings or stainless + EPDM washers.
Spec line (copy/paste)
- Material: ASTM A653 CS Type B, coating G90 (≈ Z275), minimized spangle, passivated, oiled
- Thickness: 0.60 mm base metal; cover width per profile
- Finish: PVDF 25 μm over primer (if painted)
- Edges: Slit; seal cut edges after fab in coastal sites
FAQs & internal links
Q: Is G90 enough near the coast?
A: Consider G185 or AZ150 + PVDF, plus edge sealing. See coastal guide.
Baoli Engineering Team · Reviewed Oct 31, 2025