Introduction
GI pipes (Galvanized Iron pipes) are a core component in plumbing, structural, and industrial systems across India. Their zinc coating provides excellent corrosion resistance, making them ideal for water supply lines, irrigation, borewells, fencing, and fabrication. But to ensure proper installation and compatibility, it's crucial to understand the standard GI pipe size chart in mm and inches, as defined by ISI standards (IS:1239 Part 1 and Part 2).
This guide provides a comprehensive GI pipe size chart with nominal bore (NB), outside diameter (OD), wall thickness, and equivalent inch-mm conversions, helping buyers, engineers, and plumbers make informed choices.
📌 What is a GI Pipe?
A GI pipe is a mild steel pipe that has been galvanized with a layer of zinc. The galvanization process helps prevent rust, thereby extending the pipe's lifespan. These pipes are widely used in:
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💧 Water supply and plumbing
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🚜 Agricultural irrigation
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🏗️ Structural applications
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🔩 Fabrication and railing systems
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🏠 Residential and commercial construction
📐 GI Pipe Size Chart – MM and Inch Conversion
Here’s the full ISI standard GI pipe size chart including nominal bore (NB), outside diameter (OD), and common classes (A, B, C):
| Nominal Bore (NB) | Inch Size | Outside Diameter (OD) | Wall Thickness (mm) | Common Class |
|---|
| 6 mm | ¼” | 13.5 mm | 1.8 mm (A) | A, B |
| 8 mm | ⅜” | 17.2 mm | 1.8 – 2.0 mm | A, B |
| 10 mm | ½” | 21.3 mm | 2.0 – 2.65 mm | A, B, C |
| 15 mm | ¾” | 26.9 mm | 2.0 – 2.65 mm | A, B, C |
| 20 mm | 1” | 33.7 mm | 2.6 – 3.2 mm | A, B, C |
| 25 mm | 1¼” | 42.4 mm | 2.6 – 3.25 mm | B, C |
| 32 mm | 1½” | 48.3 mm | 2.9 – 3.65 mm | B, C |
| 40 mm | 2” | 60.3 mm | 3.2 – 4.0 mm | B, C |
| 50 mm | 2½” | 76.1 mm | 3.2 – 4.5 mm | B, C |
| 65 mm | 3” | 88.9 mm | 3.6 – 4.5 mm | B, C |
| 80 mm | 4” | 114.3 mm | 4.0 – 5.4 mm | B, C |
| 100 mm | 5” | 139.7 mm | 4.5 – 5.4 mm | B, C |
| 150 mm | 6” | 168.3 mm | 5.0 – 6.0 mm | C Only |
🛠️ OD = Outer Diameter | NB = Nominal Bore (pipe ID approx.)
🔍 GI Pipe Size Classification – A, B, C Classes
The ISI standard classifies GI pipes into three types based on wall thickness:
| Class | Wall Thickness | Usage | Color Code (End Cap) |
|---|
| A Class | Light | Low pressure, temporary installations | Yellow |
| B Class | Medium | General plumbing, irrigation | Blue |
| C Class | Heavy | Industrial piping, high-pressure lines | Red |
🧮 GI Pipe Weight Chart by Size (B Class – Approximate)
| Size (NB) | Inch | OD (mm) | Weight/6m (kg) | Weight/m (kg) |
|---|
| 15 mm | ½” | 21.3 mm | ~9.3 kg | ~1.55 kg |
| 20 mm | ¾” | 26.9 mm | ~12.4 kg | ~2.07 kg |
| 25 mm | 1” | 33.7 mm | ~17.0 kg | ~2.83 kg |
| 32 mm | 1¼” | 42.4 mm | ~23.0 kg | ~3.83 kg |
| 40 mm | 1½” | 48.3 mm | ~28.8 kg | ~4.80 kg |
| 50 mm | 2” | 60.3 mm | ~37.5 kg | ~6.25 kg |
📦 Note: Exact weights vary by brand & zinc coating. Always ask for a mill certificate.
🧰 Application Guide by Size
| Size | Recommended Use |
|---|
| ½” (15mm) | Home plumbing, washbasins, taps |
| ¾” (20mm) | Garden connections, outer faucets |
| 1” (25mm) | Main supply lines in residential buildings |
| 1¼” – 1½” | Water tanks, irrigation setups |
| 2” (50mm) | Apartments, borewell connections |
| 3”+ (65mm & above) | Commercial and industrial pipelines |
🏢 ISI Standards for GI Pipe Sizes
ISI (Indian Standards Institute) standardizes GI pipes under IS:1239 Part 1 for nominal bore up to 150mm and IS:3589 for sizes above 150mm.
Key ISI Norms Include:
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Outer diameter and wall thickness tolerances
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Zinc coating thickness (min 360 g/m²)
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Tensile strength and elongation
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Hydraulic pressure test compliance
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Threading and end finish standards
✅ Pipes must be hot dip galvanized and tested under pressure for certification.
💰 GI Pipe Size vs Price Overview (2025)
| Size | Class | Avg. Price/Metre |
|---|
| ½” (15mm) | B Class | ₹95 – ₹115 |
| 1” (25mm) | B Class | ₹135 – ₹155 |
| 1½” (40mm) | B Class | ₹190 – ₹220 |
| 2” (50mm) | B Class | ₹230 – ₹270 |
| 3” (65mm) | B Class | ₹280 – ₹330 |
💡 For exact pricing by brand (Tata, Jindal, Swastik), always request a quote from verified suppliers like Udhhyog.
🛒 Where to Buy GI Pipes by Size?
✅ Udhhyog – India’s Verified GI Pipe Supplier Platform
Udhhyog helps buyers across India access standard-sized GI pipes from certified manufacturers and distributors.
📞 Visit Udhhyog.in to request your custom size quote.
📍 Size Availability by Popular Brands
| Brand | Available Sizes | Specialty |
|---|
| Tata Pipes | ½” to 6” | Highest quality, ISI-certified |
| Jindal Pipes | ½” to 8” | Cost-effective and durable |
| Swastik Pipes | ½” to 4” | Rural and affordable segment |
| Apollo | ¾” to 3” | Widely available for general use |
| Zenith | 2” to 8” | Focused on heavy industrial pipelines |
❓ FAQs – GI Pipe Size Chart
✅ What does NB (Nominal Bore) mean in GI pipes?
NB refers to the approximate internal diameter of a pipe, used as a sizing standard in millimeters.
✅ How is GI pipe size calculated in mm?
Size = Nominal Bore (NB) in mm
To get OD, add twice the wall thickness to NB. OD is standard across brands for ISI pipes.
✅ Are GI pipe sizes standardized?
Yes, ISI-certified pipes follow IS:1239 standards for wall thickness, OD, and pressure handling.
✅ Can I mix brands and sizes in the same project?
You can, but it’s recommended to use same brand + same class for consistency and safety.
🏁 Conclusion
Choosing the right GI pipe size is key to achieving optimal flow, pressure resistance, and durability in your project. With this complete GI pipe size chart in mm and inches, along with ISI standard compliance, you now have the technical clarity to select the exact size for plumbing, irrigation, or structural use.
When in doubt, partner with a verified supplier like Udhhyog to get ISI-certified, zinc-coated GI pipes in your required sizes and quantities—backed by expert support and bulk pricing options.
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