GC Sheet Weight Per Square Metre — All Thicknesses
GC (galvanised corrugated) sheet weight per square metre ranges from 3.10 kg/m² for 0.35mm thickness to 5.22 kg/m² for 0.63mm thickness, calculated per IS 277:2003 using the formula: weight = thickness (mm) ÷ 1000 × 7850 kg/m³, plus the zinc coating weight (typically 0.275 kg/m² for Z275 grade). For structural calculations, always use the weight per metre of actual roof area covered (using effective cover width), not the flat sheet area.
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XXXXXXXXXX ca-pub-XXXXXXXXXXQuick Reference — Most Common Thicknesses
- 0.35 mm GC sheet: 3.10 kg/m² (base metal) + 0.275 kg/m² (Z275 zinc) = 3.37 kg/m²
- 0.47 mm GC sheet: 3.69 kg/m² (base metal) + 0.275 kg/m² (Z275 zinc) = 3.97 kg/m²
- 0.50 mm GC sheet: 3.93 kg/m² (base metal) + 0.275 kg/m² (Z275 zinc) = 4.20 kg/m²
- IS Standard: IS 277:2003 — governs thickness, zinc coating weight, and tolerances
- Steel density used: 7850 kg/m³ (standard for mild steel per IS 2062)
The IS 277 Weight Formula
According to IS 277:2003, the nominal weight per square metre of galvanised steel sheet is calculated from the base metal (steel) weight plus the zinc coating weight:
Weight (kg/m²) = [Thickness (mm) ÷ 1000] × 7850 + Zinc coating (kg/m²)
Where:
- Thickness (mm) — the nominal base metal (steel) thickness, not including zinc. Values: 0.35, 0.40, 0.45, 0.47, 0.50, 0.55, 0.63 mm.
- 7850 kg/m³ — the density of mild steel per IS 2062. This is the standard value used across the steel industry in India.
- Zinc coating (kg/m²) — the zinc coating weight on both sides combined. For Z275 grade: 0.275 kg/m². For Z120 grade: 0.120 kg/m².
Example Calculation — 0.47mm GC Sheet, Z275
Base metal: 0.47 ÷ 1000 × 7850 = 0.000470 × 7850 = 3.690 kg/m²
Zinc (Z275): 0.275 kg/m²
Total weight: 3.690 + 0.275 = 3.965 ≈ 3.97 kg/m²
GC Sheet Weight Per m² — Complete Table (All Thicknesses)
| Nominal Thickness (mm) | Base Metal (kg/m²) | Z120 Total (kg/m²) | Z275 Total (kg/m²) | Typical Application |
|---|---|---|---|---|
| 0.35 mm | 2.75 | 2.87 | 3.02 | Light duty, indoor |
| 0.40 mm | 3.14 | 3.26 | 3.42 | Residential, low wind |
| 0.45 mm | 3.53 | 3.65 | 3.80 | Residential standard |
| 0.47 mm | 3.69 | 3.81 | 3.97 | Most popular — residential/industrial |
| 0.50 mm | 3.93 | 4.05 | 4.20 | Industrial shed |
| 0.55 mm | 4.32 | 4.44 | 4.59 | Heavy industrial, coastal |
| 0.63 mm | 4.95 | 5.07 | 5.22 | High wind zone, long span |
All weights calculated using IS 277:2003 formula: (thickness ÷ 1000) × 7850 kg/m³ + zinc coating weight. Z120 = 0.120 kg/m²; Z275 = 0.275 kg/m². Tolerance ±3% on weight per IS 277. Values for flat sheet equivalent.
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XXXXXXXXXX ca-pub-XXXXXXXXXXUnderstanding Zinc Coating Weight
The zinc coating weight is expressed as grams per square metre (g/m²) of total zinc on both sides combined. Common grades in India per IS 277:
| Grade | Total Zinc (g/m², both sides) | Zinc Weight (kg/m²) | Approx. Zinc Thickness (each side) | Recommended Use |
|---|---|---|---|---|
| Z120 | 120 g/m² | 0.120 kg/m² | ~8.5 µm per side | Temporary, indoor, low humidity |
| Z180 | 180 g/m² | 0.180 kg/m² | ~12.7 µm per side | Low-exposure inland |
| Z275 | 275 g/m² | 0.275 kg/m² | ~19.5 µm per side | Standard roofing — most brands supply this |
| Z350 | 350 g/m² | 0.350 kg/m² | ~24.8 µm per side | Aggressive environments |
| Z450 | 450 g/m² | 0.450 kg/m² | ~31.9 µm per side | Coastal, industrial acid zones |
Most GC roofing sheets sold in India by major brands (Tata Shaktee, JSW, Jindal) are Z275. Always confirm the zinc grade on the test certificate before purchase. Cheaper unbranded sheets may be Z120 or Z180, which will show corrosion significantly sooner.
Nominal vs Actual Weight — What the Difference Means
IS 277:2003 allows a weight tolerance of ±3% on any individual sheet and ±2% on a lot average. This means a 0.47mm Z275 sheet with a nominal weight of 3.97 kg/m² may actually weigh between 3.85 and 4.09 kg/m² and still be fully compliant.
Additionally, there is a difference between flat-sheet weight and profiled-sheet weight. A corrugated sheet has a longer path across the corrugations than a flat sheet of the same plan width. The development length of a standard sinusoidal corrugated profile (pitch 76 mm, depth 19 mm) is approximately 5.6% greater than the flat width. This means the actual material weight of a corrugated sheet is about 5.6% more than the flat-sheet weight formula gives.
For practical purposes, most dealers quote and charge by flat-sheet weight (the IS 277 formula value). When doing structural load calculations, use the flat-sheet weight per m² of plan area — this accounts for the slope and development length simultaneously and gives the correct dead load on the structure.
Using Sheet Weight in Structural Calculations
Structural engineers calculate roof dead load as weight per square metre of plan area (horizontal projection), not slope area. This simplifies load path calculations since tributary area is measured on plan.
For a typical GC sheet roof the dead load components are:
| Component | Weight (kg/m² of plan area) |
|---|---|
| GC sheet (0.47mm Z275) | 3.97 |
| Purlins (ISA 50×50×6 @ 1200mm c/c) | 1.50–2.00 |
| Ridge cap + fixings | 0.20–0.30 |
| Self-drilling screws + washers | 0.10–0.15 |
| Total dead load (approx.) | 5.8–6.4 kg/m² |
Convert to kPa for structural use: 6.1 kg/m² × 9.81 ÷ 1000 = 0.060 kPa dead load. This is consistent with typical values used in Indian industrial shed design (0.05–0.08 kPa for GC sheet roofing per IS 875 Part 1 — Dead Loads).
Calculate Total Roof Weight for Your Project
Enter your roof area, sheet thickness, and profile into the Roof Weight Calculator to get total dead load in kg — useful for purlin and truss design.
Open Roof Weight CalculatorFrequently Asked Questions
What is the weight of a 0.47mm GC sheet per square metre?
A 0.47mm GC sheet with Z275 zinc coating weighs approximately 3.97 kg/m² as a flat sheet. Calculated using IS 277: (0.47 ÷ 1000) × 7850 = 3.69 kg/m² base metal + 0.275 kg/m² zinc = 3.97 kg/m². For corrugated profile (5.6% development factor) the actual material weight is about 4.19 kg/m² of flat area, but for structural dead load calculations always use the 3.97 kg/m² plan area value.
How do I calculate the total weight of GC sheets for a shed roof?
Multiply the total plan roof area (length × width, both slopes if applicable) by the weight per m² for your chosen thickness. For a 20×30 ft (6.1m × 9.1m) shed with 0.47mm Z275 GC sheet: plan area = 6.1 × 9.1 = 55.5 m². Total sheet weight = 55.5 × 3.97 = 220 kg approximately. Use our Roof Weight Calculator to include purlin and fixings weight as well.
What does Z275 mean on a GC sheet?
Z275 is the zinc coating grade per IS 277. It means the sheet has a minimum of 275 grams of zinc per square metre total on both sides combined. Z275 is approximately 19.5 microns of zinc on each side. This is the standard grade for roofing sheets sold by major Indian brands (Tata Shaktee, JSW, Jindal). Lower grades (Z120, Z180) have thinner zinc and shorter corrosion life.
Is the thickness marked on a GC sheet the total thickness or just the steel?
Per IS 277:2003, the nominal thickness stated for a GC sheet refers to the base metal (steel) thickness only, not including the zinc coating. A "0.47mm sheet" contains 0.47mm of steel plus approximately 0.039mm of zinc (0.02mm per side for Z275 grade). The total physical thickness of the coated sheet is approximately 0.509mm. Always specify base metal thickness when ordering — this is the standard way the industry describes sheets in India.
Why does the actual sheet weight sometimes differ from the stated weight?
IS 277 allows a weight tolerance of ±3% on individual sheets and ±2% on lot averages. So a 0.47mm Z275 sheet with nominal weight 3.97 kg/m² may weigh anywhere from 3.85 to 4.09 kg/m² and still comply. Additionally, corrugated sheets are slightly heavier than the flat formula suggests because the corrugation profile adds approximately 5.6% to the material path length. Reputable brands publish test certificates showing actual average weight per lot.