GI sheet is mild steel sheet coated on both sides with zinc by hot-dip galvanising, made in India to IS 277. The zinc protects the steel from rust. Coating is given in grams per square metre (both sides together), such as Z120 or Z275: more zinc lasts longer. GI sheet is used for ducts, electrical panels, enclosures, roofing, cable trays and sheet metal parts.
Quick facts
- Standard
- IS 277
- Base
- Mild steel sheet
- Coating
- Zinc, classes such as Z90, Z120, Z180, Z275 (g/m², both sides)
- Thickness
- About 0.3–3 mm (0.0118–0.118 inch) common
- Finish
- Regular spangle or zero spangle
- Also called
- GP sheet (galvanised plain)
Choosing the coating
| Coating | Typical use |
|---|---|
| Z90–Z120 | Indoor parts, panels to be painted |
| Z180 | General use, ducts |
| Z275 | Outdoor parts, roofing, longer life |
Typical choices; outdoor and coastal sites need heavier coatings or extra paint.
Working with GI sheet
- Bends well; very heavy coatings may flake on sharp bends
- Welding burns off zinc: weld with good ventilation and repair the area with zinc-rich paint
- Laser and plasma cut edges are not protected by zinc
- Powder coating needs proper pre-treatment for good adhesion
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Questions
- What does Z275 mean?
- 275 grams of zinc per square metre of sheet, counting both sides together.
- GI or GP sheet?
- They usually mean the same thing in India: galvanised plain sheet.
- Is GI the same as hot-dip galvanising of parts?
- Both are zinc coatings, but GI sheet is coated before fabrication; parts can be hot-dip galvanised after fabrication for a thicker coat.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 29 October 2026.