Short answer
What are PVC pipe sizes in mm and inches? Indian Standards size plastic pipes by outside diameter in millimetres, not inches. A UPVC pipe sold as 1/2 inch is 20 mm outside under IS 4985, a CPVC pipe sold as 1/2 inch is 15.9 mm under IS 15778, and a schedule 40 UPVC pipe sold as 1/2 inch is 21.34 mm. So read the standard and the size printed on the pipe, and buy fittings made for that same pipe.
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At the hardware shop, pipes are asked for in inches: “half inch”, “one inch”, “four inch”. The Indian Standards size them in millimetres, by outside diameter. And the same inch name means a different real size for UPVC, CPVC and drainage pipe. This page gives the size tables from the Indian Standards and from makers’ catalogues, explains what the numbers printed on a pipe mean, and shows how to avoid buying fittings that do not match. It gives no prices, ranks no brand, and does not tell you which size to use where: that is your plumber’s or engineer’s design.
Why is a “1/2 inch” pipe not 1/2 inch wide?
The inch name is a trade name, not a measurement. None of the three Indian Standards for these pipes uses inches at all.
- IS 4985, for UPVC water-supply pipes, and IS 13592, for UPVC soil, waste and rainwater (SWR) pipes, name each pipe by its outside diameter in millimetres. A 20 mm pipe is about 20 mm across the outside.
- IS 15778, for CPVC hot and cold water pipes, uses a “nominal size” that is only “a convenient round number approximately equal to the manufacturing dimensions”. Its size 15 pipe is 15.9 mm across the outside, and its size 25 pipe is 28.6 mm.
On top of that, some UPVC plumbing pipe in Indian shops is made to the American standard ASTM D1785 (schedule 40 and 80) in inch sizes, with yet another set of outside diameters. So “1/2 inch” can mean three different pipes.
| Trade name | UPVC to IS 4985 | CPVC to IS 15778 | UPVC schedule pipe to ASTM D1785 |
|---|---|---|---|
| 1/2 inch | 20 mm | 15.9 mm | 21.34 mm |
| 3/4 inch | 25 mm | 22.2 mm | 26.67 mm |
| 1 inch | 32 mm | 28.6 mm | 33.40 mm |
| 1 1/4 inch | 40 mm | 34.9 mm | 42.16 mm |
| 1 1/2 inch | 50 mm | 41.3 mm | 48.26 mm |
| 2 inch | 63 mm | 54.0 mm | 60.32 mm |
All figures are outside diameters. The inch names come from makers’ catalogues (Finolex for IS 4985 and CPVC; Astral and Prince for ASTM D1785). The IS 4985 and IS 15778 millimetre figures match the standards’ tables; the ASTM figures are from those catalogues. Other makers may label sizes differently, so check the catalogue of the pipe you buy.
What are the UPVC pipe sizes in IS 4985?
IS 4985:2021 lists water-supply pipes by nominal outside diameter, from 20 mm up to 630 mm. The sizes a house usually meets, with the inch names used in one maker’s catalogue:
| Outside diameter (IS 4985) | Inch name (Finolex catalogue) |
|---|---|
| 20 mm | 1/2 inch |
| 25 mm | 3/4 inch |
| 32 mm | 1 inch |
| 40 mm | 1 1/4 inch |
| 50 mm | 1 1/2 inch |
| 63 mm | 2 inch |
| 75 mm | 2 1/2 inch |
| 90 mm | 3 inch |
| 110 mm | 4 inch |
| 160 mm | 6 inch |
IS 4985 also has a separate table of “plumbing” pipes for use inside buildings, in sizes 20 to 50 mm, which must carry the word “plumbing” in their marking. They have no pressure class: the standard says their thicker wall is for rigidity, not for a higher working pressure.
What are the CPVC pipe sizes in IS 15778?
| Nominal size (IS 15778) | Outside diameter | Inch name (makers’ catalogues) |
|---|---|---|
| 15 | 15.9 mm | 1/2 inch |
| 20 | 22.2 mm | 3/4 inch |
| 25 | 28.6 mm | 1 inch |
| 32 | 34.9 mm | 1 1/4 inch |
| 40 | 41.3 mm | 1 1/2 inch |
| 50 | 54.0 mm | 2 inch |
| 65 | 73.0 mm | 2 1/2 inch |
| 80 | 88.9 mm | 3 inch |
| 100 | 114.3 mm | 4 inch |
IS 15778 says its sizes follow Indian manufacturing practice derived from American standards (ASTM F 442M and ASTM D 2846M). That is why a “25” CPVC pipe is not 25 mm across. The inch names for sizes 15 to 50 come from makers’ IS 15778 tables. Above 2 inch, makers we checked sell CPVC as schedule pipe to the American standard ASTM F 441, with the same outside diameters as the 65, 80 and 100 rows above.
What are the SWR pipe sizes in IS 13592?
SWR pipes carry soil (toilet) waste, other waste water, vent air and rainwater. IS 13592:2013 designates them by nominal outside diameter in millimetres: 40, 50, 63, 75, 90, 110, 125, 140, 160, 180, 200, 250 and 315 mm. One maker’s catalogue names 75 mm as 2 1/2 inch, 90 mm as 3 inch, 110 mm as 4 inch and 160 mm as 6 inch.
IS 13592 has two types:
- Type A for ventilation and rainwater.
- Type B for soil and waste.
The marking on the pipe says which type it is, and IS 13592 sets a marking colour for each: blue for Type A and white for Type B. Type A is made only up to 160 mm. SWR pipes have no pressure class: they are drainage pipes, not for water under pressure. SWR fittings are sized by their sockets to match these pipe diameters (IS 14735).
What do the markings on the pipe mean?
The standards ask every pipe to be marked along its length. Read the marking before you buy.
| On the pipe | UPVC (IS 4985) | CPVC (IS 15778) | SWR (IS 13592) |
|---|---|---|---|
| Size | Outside diameter | Outside diameter | Nominal outside diameter |
| Class or type | Class and pressure rating; the word “plumbing” for plumbing pipes | Class and pressure rating | Type A or Type B |
| Other | Maker, batch | Maker, batch | Maker, batch |
Class numbers do not mean the same thing in UPVC and CPVC. In IS 4985, Class 1 is the lowest pressure and Class 6 the highest, and the marking on the pipe is in a colour for each class (red for Class 1 up to black for Class 6; pink for plumbing pipes). The pipe itself is normally light grey. In IS 15778, Class 1 is the thickest, highest-pressure CPVC pipe of its classes. So “Class 1” on a UPVC pipe and “Class 1” on a CPVC pipe are very different.
Class is not a thickness either. In IS 4985 the wall thickness for a class changes with the pipe size. To know a pipe’s wall, you need both its size and its class, and the standard’s table.
What mistakes should I avoid?
These come from the standards’ tables and from site practice:
- Buying fittings by the printed number across systems. A “25” UPVC fitting will not fit a “25” CPVC pipe, because one pipe is 25 mm across and the other is 28.6 mm. The same goes for IS 4985 metric pipe and ASTM schedule pipe. Buy pipe and fittings of the same standard, ideally from the same system. (This is our reading of the size tables; your plumber will confirm.)
- Treating “1 inch” as one size. Always ask which standard the pipe is made to.
- Comparing class numbers across UPVC and CPVC.
- Using SWR pipe for a water supply line. It has no pressure rating.
- Using Type A SWR pipe for toilet or kitchen waste. IS 13592 assigns soil and waste to Type B.
- Going by colour. Read the marking. Our guide to CPVC vs UPVC pipes explains why colour is not a safe guide, and which pipe suits hot water.
Frequently asked questions
What is 1 inch PVC pipe in mm?
It depends on the pipe. A UPVC pipe to IS 4985 sold as 1 inch is 32 mm outside, a CPVC pipe sold as 1 inch is 28.6 mm, and a schedule 40 UPVC pipe sold as 1 inch is 33.40 mm, according to the makers’ catalogues and standards cited here.
Is PVC pipe size the inside or the outside diameter?
For IS 4985 and IS 13592 pipes, the outside diameter in millimetres. CPVC and schedule pipe use a nominal size, and the standard’s table gives the outside diameter for it. The inside size depends on the wall thickness, which changes with the class.
Is 25 mm CPVC the same as 25 mm UPVC?
No. Under IS 15778 a size 25 CPVC pipe is 28.6 mm across the outside. Under IS 4985 a 25 mm UPVC pipe is 25 mm across. Their fittings are not interchangeable.
What does Class 1, 2 or 3 mean on a pipe?
On UPVC pipe to IS 4985, the class is the pressure rating, from Class 1 (lowest) to Class 6 (highest). On CPVC pipe to IS 15778, Class 1 is the highest-pressure class. Read the pressure rating printed beside the class.
What size pipe is used for bathroom plumbing?
That is a design choice for your plumber or engineer, based on the fixtures and the water pressure. This page gives sizes, not a design. Ask for the sizes to be written on the plumbing drawing.
Related guides
- CPVC vs UPVC pipes: which one to use for home plumbing
- Bathroom waterproofing: steps, wall height and the ponding test
This guide is general information. Read the disclaimer. Your plumber or engineer decides the pipe material, class and size for each line, following the drawings and the maker’s instructions.
Sources
- IS 4985:2021, Unplasticized PVC Pipes for Water Supplies - Specification (Fourth Revision), with Amendment 1 (2023). Clauses 3, 5.1, 10.1, 11.1.1, 13 and Tables 1 and 2.
- IS 15778:2007, Chlorinated Polyvinyl Chloride (CPVC) Pipes for Potable Hot and Cold Water Distribution Supplies - Specification. Foreword, clauses 3, 12 and Tables 1 and 2.
- IS 13592:2013, Unplasticized PVC (PVC-U) Pipes for Soil and Waste Discharge System Inside and Outside Buildings Including Ventilation and Rain Water System - Specification (First Revision). Clauses 3, 4, 14 and Table 1.
- IS 14735:1999, UPVC Injection Moulded Fittings for Soil and Waste Discharge System. Clause 4 (size designation).
- Finolex Pipes, PVC-U agriculture pipes brochure (IS 4985 size table with inch names).
- Finolex Pipes, CPVC pipes brochure (IS 15778 size table with inch names).
- Finolex Pipes, SWR pipes brochure (IS 13592 size table with inch names).
- Prince Pipes, all-product catalogue (ASTM D1785 schedule 40/80 UPVC and ASTM F 441 CPVC size tables).
- Astral Pipes, Aquarius UPVC plumbing catalogue, July 2023 (ASTM D1785 schedule 40 and 80 size table).
General information only. It is not a structural design or professional advice. Ask a licensed structural engineer or architect to check your plans and site.