Table of contents

What is a GI coil?
GI coil specifications and sizes
What is a GI C channel?
GI C channel sizes and dimensions
Where GI coil and GI C channel are used
GI coil vs GI C channel: key differences
The last word
FAQs

A GI coil is flat, zinc-coated steel supplied in roll form, the raw material fabricators cut and shape into finished parts. A GI C channel is a C-shaped section, roll-formed from galvanised steel and used largely as-is for framing and support.

Both carry a zinc coating for corrosion resistance, but they sit at opposite ends of the supply chain. Buyers sourcing one sometimes assume the other follows the same standard, sizing logic or coating rules; it does not.

This guide sets out the governing IS standards, size ranges, weight calculation, and where each product is actually used, so procurement teams and site engineers order the right one the first time.

What is a GI coil?

A GI coil is a continuous roll of steel, cold-rolled or hot-rolled, coated with zinc through a hot-dip process. It is manufactured under IS 277:2018, the Bureau of Indian Standards specification for galvanised steel strips and sheets, which sets zinc coating mass in classes from Z120 to Z600, denoting 120 to 600 grams per square metre combined across both faces.

The base strip is cleaned, annealed where the grade requires it, and then passed through a molten zinc bath. Lighter classes such as Z120 to Z200 suit indoor, low-corrosion use like HVAC ducting; heavier classes from Z275 upward suit roofing, cladding and coastal or industrial exposure. Thickness alone says nothing about corrosion life, so both figures belong on every purchase order and test certificate.

GI coil specifications and sizes

Standard GI coil under IS 277:2018 covers thickness from 0.14 mm to 4.0 mm, in widths from 600 mm to 1,500 mm, with inner coil diameters typically 508 mm or 610 mm.

Parameter	Typical range
Thickness	0.14 mm – 3.2 mm
Width	600 mm – 1,400 mm
Coil inner diameter	508 mm or 610 mm
Zinc coating class	Z120 to Z600 (120–600 g/m², both faces)
Governing standard	IS 277:2018

Parameter	Typical range
Parameter	Typical range
Thickness	0.14 mm – 3.2 mm
Width	600 mm – 1,400 mm
Coil inner diameter	508 mm or 610 mm
Zinc coating class	Z120 to Z600 (120–600 g/m², both faces)
Governing standard	IS 277:2018

Knowing a coil's weight matters for freight cost and handling before an order is placed. The steel industry's standard shorthand is:

Weight (kg) = Length (m) × Width (m) × Thickness (mm) × 7.85

Here, 7.85 is steel's density, with the unit conversion built into the constant. A coil 500 metres long, 1.2 metres wide and 0.6 mm thick works out to approximately 2,826 kg before the zinc coating is added. The coating itself adds a small amount of extra mass, more noticeable on thinner sheet: a Z275 coating adds roughly 3.5% to a 1 mm sheet but 7 to 8% to a 0.5 mm sheet, since the zinc makes up a larger share of the total.

What is a GI C channel?

A GI C channel is a cold-formed, C-shaped steel section, roll-formed from galvanised strip or sheet rather than cast or hot-rolled to shape. It is a finished structural member, not a raw material: fabricators cut it to length and bolt or weld it directly into a frame.

Two manufacturing routes exist. Pre-galvanised channel is roll-formed from coil that already carries its zinc coating, which is lighter and quicker to fabricate. Post-galvanised channel is roll-formed first, then hot-dip coated afterwards, giving a heavier, more complete coating better suited to demanding load-bearing use. Confirm which route a supplier used before ordering, since it affects both weight and coating coverage at cut edges.

A GI C channel should not be confused with a hot-rolled ISMC channel. ISMC sections are hot-rolled to shape under IS 808:2021 and used as primary structural members. GI C channels are cold-formed, lighter-gauge, and used for secondary framing such as purlins and wall girts, not as load-bearing beams in their own right.

GI C channel sizes and dimensions

Dimensions and sectional properties for cold-formed sections sit under IS 811:1987, which covers dimensions and section properties, and IS 801:1975, which covers design and use — not under IS 808, which governs hot-rolled sections instead.

Parameter	Typical range
Depth	100 mm – 400 mm
Material thickness	1.2 mm – 3.0 mm
Governing standards	IS 811:1987 (dimensions), IS 801:1975 (design)

Unlike hot-rolled ISMC, which follows one fixed national size table, cold-formed C channel dimensions vary by manufacturer rather than sitting in a single published IS 811 size chart. The ranges above are indicative. Confirm exact depth, flange width, lip size and weight per metre against a specific supplier's datasheet before finalising a bill of quantities.

Where GI coil and GI C channel are used

GI coil is a raw material, processed further into roofing sheets, HVAC ducting, electrical enclosures, automotive panels, and pipes and tubes. A GI C channel is installed largely as supplied, cut to length rather than reshaped.

GI coil: roofing and wall cladding, HVAC ducting, electrical panel fabrication, automotive body parts, pipe and tube manufacture.

GI C channel: roof purlins and wall girts, secondary framing in pre-engineered buildings, and light-gauge steel framing for industrial sheds and warehouses.

Both rely on galvanising for the same reason. Zinc corrodes at roughly one-thirtieth the rate of bare steel, and a correctly specified coating can protect steel for decades before first maintenance, according to the American Galvanizers Association.

GI Coil & GI C Channel: Recommended Specifications

Application	Product	Recommended thickness	Recommended coating
Roofing & wall cladding	GI Coil	0.40–0.60 mm	Z275
HVAC ducting	GI Coil	0.40–0.60 mm	Z120–Z180
Electrical panels	GI Coil	0.80–1.20 mm	Z120–Z180
Roof purlins & wall girts	GI C Channel	1.6–3.0 mm	Z275–Z450
Light industrial framing	GI C Channel	2.0–3.0 mm	Z275–Z450
Coastal applications	GI Coil / GI C Channel	As per design	Z450–Z600

GI coil vs GI C channel: key differences

Coil and channel sit at different points in the supply chain, and that shapes almost every other difference between them.

Aspect	GI coil	GI C channel
Form	Flat, continuous roll	Pre-formed C-section
Primary use	Raw material for further processing	Ready-to-install structural member
Governing standard	IS 277:2018	IS 811:1987 and IS 801:1975
Processing needed	Slitting, roll-forming, stamping	Cutting to length, drilling, welding
Typical buyer	Fabricators, OEMs, re-rollers	Contractors, structural engineers

Demand for both is rising with India's construction cycle. Finished steel consumption grew 8.3% year-on-year to 41.6 million tonnes in the April to June 2026 quarter, and galvanised sheet prices rose 15.8% over the same period, according to Ministry of Steel data. Secondary producers, including MSMEs, accounted for 47% of India's crude steel capacity in FY25, per IBEF.

GI coil vs GI C channel: making the right choice

Choosing between the two comes down to where the material sits in the build: coil gives fabricators the flexibility to shape custom parts, while channel arrives ready to bolt or weld into a frame.

Before ordering either, confirm the zinc coating class against the exposure environment, check dimensions against IS 277:2018 for coil or IS 811:1987 for channel, and ask the supplier for a material test certificate.

Compare GI coil options on JSW One MSME.

Have a specification question? Get in touch with the team for guidance before you place an order.

Key takeaways

GI coil is a flat, zinc-coated raw material governed by IS 277:2018, while GI C channel is a finished, cold-formed structural section governed by IS 811:1987 and IS 801:1975, not IS 808.
Zinc coating classes for GI coil run from Z120 to Z600, denoting 120 to 600 grams per square metre combined across both faces.
A GI C channel should not be confused with a hot-rolled ISMC channel, which is a heavier, primary structural member governed by a different standard.
Coil weight is estimated from length, width, thickness and steel density, with the zinc coating itself adding roughly three to eight percent extra mass depending on sheet thickness.
Demand for both products is rising with India's construction cycle, with finished steel consumption up 8.3% year-on-year to 41.6 million tonnes in the April to June 2026 quarter.

FAQs

What is the difference between a GI coil and a GI C channel?

A GI coil is flat, zinc-coated steel supplied in roll form as a raw material for further processing. A GI C channel is a finished, cold-formed structural section, ready to install as purlins, girts or framing. They are governed by different standards and rarely substitute for one another.

How do I calculate the weight of a GI coil?

Multiply length (m) by width (m) by thickness (mm) by 7.85. A 500 m coil, 1.2 m wide and 0.6 mm thick weighs approximately 2,826 kg before the zinc coating, which adds a further three to eight percent depending on sheet thickness and coating class.

Can a GI C channel be welded without damaging the galvanising?

Yes, but welding burns off zinc in the heat-affected zone. Standard practice is to weld first, then apply a zinc-rich cold-galvanising compound to restore corrosion protection before the section enters service.

What zinc coating class suits outdoor structural framing?

Z275 to Z350 is common for India's tropical and coastal climate, with Z450 and above used for marine or heavy-industrial exposure. A heavier class generally means a longer maintenance-free life, since zinc corrodes at roughly one-thirtieth the rate of bare steel.

What is the standard inner diameter of a GI coil?

Indian GI coils are typically supplied with a 508 mm or 610 mm inner diameter, to match standard decoiler equipment.

What affects GI coil prices?

GI coil prices depend on several factors, including base steel prices, thickness, width, zinc coating class, steel grade, order quantity, and delivery location. As steel prices fluctuate, GI coil prices also change. Check live GI coil prices on JSW ONE MSME for the latest rates and availability.

Is a GI C channel the same as an ISMC channel?

No. ISMC channels are hot-rolled under IS 808:2021 and used as primary structural members. GI C channels are cold-formed from galvanised strip under IS 811:1987, lighter-gauge, and used mainly for secondary framing such as purlins and girts.

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