CPVC Pipe Size Chart in mm and Inches: A Practical Sizing Guide for Engineers

CPVC Pipe Sizes in mm and Inches: The Chart Only Tells Half the Story

Outside diameter, wall thickness and schedule decide whether a CPVC system fits together, holds its pressure rating and stays leak-free. Here is how to read the numbers correctly.

You have a process line to design or an old CPVC run to rebuild. The drawing says "CPVC, 50 mm, Schedule 80"; the supplier's catalog says "2-inch NPS, Schedule 80". They look like the same pipe. They are not. A 2-inch NPS pipe has an outside diameter of 60.3 mm; a DN50 metric pipe made to the GB series has an OD of 63 mm. Less than three millimeters separates them, yet that gap decides whether a socket fitting seats, whether a flange aligns, and whether the joint holds pressure.

Why a Nominal CPVC Size Doesn't Tell You the Real Diameter

CPVC pipe is ordered by a nominal designation, never by an actual measurement. The inch-based world uses NPS (Nominal Pipe Size) and follows the IPS outside diameter table developed for steel pipe. Under this convention the outside diameter is fixed per NPS; Schedule 40 and Schedule 80 of the same NPS share the same OD, and only the bore changes with wall thickness.

The metric world uses DN, tied to an ISO-derived outside diameter series. DN values look similar to NPS, but the outside diameters differ:

1/2" NPS CPVC has an OD of 21.3 mm (0.840 in); DN15 metric CPVC has an OD of 20 mm.
1" NPS CPVC has an OD of 33.4 mm (1.315 in); DN25 metric CPVC has an OD of 32 mm.
6" NPS CPVC has an OD of 168.3 mm (6.625 in); DN150 metric CPVC has an OD of 160 mm.

Those differences do not look serious on a datasheet, but they accumulate in the field: misaligned flanges, loose cement joints, fittings that need adapters. Decide which standard governs the entire line before you order the first length.

CPVC Pipe Size Chart in mm and Inches: Schedule 40 and 80

The table below covers CPVC pipe made to ASTM F441, with outside diameters in both inches and millimeters and wall thicknesses for Schedule 40 and Schedule 80.

Table 1. CPVC pipe dimensions per ASTM F441. The outside diameter is fixed for each NPS; inside diameter and wall thickness change with schedule.
NPS (in)	Outside Diameter (mm)	Outside Diameter (in)	Sch 40 Wall (mm)	Sch 40 Wall (in)	Sch 80 Wall (mm)	Sch 80 Wall (in)
1/2	21.3	0.840	2.77	0.109	3.73	0.147
3/4	26.7	1.050	2.87	0.113	3.91	0.154
1	33.4	1.315	3.38	0.133	4.55	0.179
1-1/4	42.2	1.660	3.56	0.140	4.85	0.191
1-1/2	48.3	1.900	3.68	0.145	5.08	0.200
2	60.3	2.375	3.91	0.154	5.54	0.218
2-1/2	73.0	2.875	5.16	0.203	7.01	0.276
3	88.9	3.500	5.49	0.216	7.62	0.300
4	114.3	4.500	6.02	0.237	8.56	0.337
6	168.3	6.625	7.11	0.280	10.97	0.432
8	219.1	8.625	8.18	0.322	12.70	0.500

What the Schedule Number Really Determines

Since the outside diameter is fixed, a thicker schedule means a smaller flow bore. At equal flow, Schedule 80 runs at a slightly higher fluid velocity than Schedule 40 of the same NPS. In chemical service that trade-off is acceptable: the thicker wall adds pressure capacity, creep resistance and tolerance for mechanical abuse.

CPVC keeps useful mechanical strength up to roughly 200°F (93°C), which is why it replaces standard PVC in hot corrosive service. Datasheet pressure ratings are computed at 73°F (23°C) and fall as temperature rises; at 180°F the allowable working pressure is typically about one-quarter of the cold rating. Compare the derated figure with the maximum pump pressure before finalizing the schedule.

A CPVC size is three numbers: outside diameter, wall thickness, and the temperature at which the pressure rating was calculated. Name all three and the rest of the system follows.

The Metric GB Series: Same Nominal, Different Diameter

When a project is documented in millimeters, the pipe is usually specified to the GB/ISO metric outside diameter series used across Asia and in exported plants. The chart looks similar, but the numbers are different:

Table 2. Common GB metric CPVC pipe sizes. Wall thickness depends on the PN pressure class specified for the line.
DN	Outside Diameter (mm)	Outside Diameter (in)	Typical Wall Range (mm)
15	20	0.787	2.0 to 3.0
25	32	1.260	2.4 to 4.0
50	63	2.480	3.0 to 6.0
80	90	3.543	4.0 to 7.0
100	110	4.331	4.2 to 8.0
150	160	6.299	5.0 to 10.0
200	225	8.858	6.0 to 12.0
300	315	12.402	8.0 to 16.0
600	630	24.803	15.0 to 30.0

Compare the collisions: DN50 is 63 mm OD against 60.3 mm for 2-inch NPS; DN80 is 90 mm against 88.9 mm for 3-inch NPS. Small enough to miss on a drawing, large enough to ruin a cemented joint. Specified to one standard, the whole line should be bought in that standard.

Matching Fittings, Flanges and Valves to the Pipe Size

Fittings and valves are labeled by the pipe they are meant to join. A socket fitting is bored to the outside diameter of the pipe, so a 2-inch NPS socket will not accept a DN50 metric pipe in a cemented joint, even though both are nominally "50". Threaded connections add another constraint: thread form and body material must come from the same standard family.

Before adding a branch, measure the pipe OD with a caliper: the actual outside diameter matters, not the packing list. If the existing line is built to ANSI/ASTM dimensions, keep new fittings in that series; a GB line gets GB fittings.

What to Define Before You Order

Write the specification so it cannot be misinterpreted. For every CPVC line, state the governing standard, outside diameter, wall thickness or schedule, service temperature and pressure class, then check every component against those figures.

Confirm the governing standard: ASTM/ANSI (NPS, inch OD) or GB/ISO (DN, metric OD).
Define the schedule or wall class: Schedule 40, Schedule 80 or PN in metric systems.
Set the maximum operating temperature and derate the pressure rating to that temperature.
Choose the connection method (socket, butt fusion, threaded or flanged) and verify that all components share the same OD series.
Account for thermal expansion with loops, offsets or expansion joints; CPVC expands noticeably more than carbon steel.
Specify hanger spacing for the selected schedule so horizontal runs do not sag between supports.

Ask the supplier for a dimensional test report and compare the OD and wall thickness tolerances against the standard in the specification, not the nominal label. The tolerance band matters at a socket joint.

For aggressive or abrasive media, dimensions are only half the job; material selection and valve design deserve equal attention. This guide to choosing the right plastic valve and pipe for corrosive and abrasive applications covers the criteria that prevent early failure.

Mistakes That Create Rework in the Field

Never join ASTM and GB pipe of the same nominal size in one solvent-cemented run. The OD difference, often less than a millimeter, produces a joint that looks assembled but weeps under pressure.

Treating the nominal size as an actual measurement. The label is a reference, not a dimension.
Applying the room-temperature pressure rating at 180°F without derating.
Assuming that because a fitting fits, the entire standard matches. Check the OD, wall thickness, thread form and flange bolt circle.
Ordering gaskets, glue and repair couplings without the OD specification and discovering on site that the part belongs to the other metric series.

The most expensive field mistake is substituting Schedule 40 for Schedule 80 on a line designed for the thicker wall. The two share fittings, but their pressure capacity at temperature and long-term creep performance differ; a failure on a hot acid line is not a maintenance event but a safety event.

A correctly specified CPVC line almost designs itself: one standard, one OD series, one schedule, one derating condition, and components from the same family.

A pipe size chart in millimeters and inches is only useful when you know which system it represents. If the chart is built on IPS outside diameters and your project is engineered to the GB metric series, the nominal numbers will mislead you. Confirm the actual ODs on the drawings, verify the derated pressure at the service temperature, and only then choose the schedule. The full CPVC range for corrosion-resistant systems is described in the product catalog, with each size family listed against its standard.