How to Read PVC Pipe Markings
PVC pipe is marked with its size and its schedule, usually after the manufacturer name. Look for the size in inches, then for SCH 40, SCH 80 or SCH 120. The size is a nominal name, so the pipe measures larger across the outside than the number printed.
- Find the size, printed as a fraction or a decimal, such as 3/4 in. or 1.25 in.
- Find the schedule, printed as SCH 40, SCH 80 or SCH 120.
- Check the other markings, such as ASTM D1785 and the pressure rating, if you need them.
- If the pipe has no markings, measure the outside diameter and match it to a size chart.
Pipe Marking Examples
Look for the PVC Size
The size is usually printed near the start of the marking, after the manufacturer name. It may appear as a fraction, such as 3/4", as a number followed by IN, or as a decimal, such as 1.25".
Decimals are the same nominal sizes: 0.5" is 1/2", 0.75" is 3/4", 1.25" is 1-1/4" and 1.5" is 1-1/2".
The printed size is a nominal size, which is a name and not a measurement. A pipe marked 3/4" measures 1.050" across the outside. To check the real measurements, see the PVC Pipe Size Dimensions Chart or compare your pipe with everyday objects on the PVC Pipe Size Comparison Chart.
Look for the PVC Schedule
The schedule is printed as SCH 40, Schedule 40 or Sched. 40. It describes the wall thickness of the pipe. Schedule 40 is the most common, Schedule 80 has a thicker wall, and Schedule 120 has the thickest wall and is the least common.
Pipe of the same size has the same outside diameter in every schedule. A thicker wall means a smaller inside diameter.
The schedule matters for fit. FORMUFIT internal-fit products work only with Schedule 40 pipe. External-fit products work with Schedule 40, Schedule 80 and thinwall pipe.
What the Other Markings Mean
Most pipe carries more than the size and schedule. These are the markings you are most likely to see. Only the size and schedule affect how the pipe fits FORMUFIT products.
| Marking | What it means | Does it affect fit? |
|---|---|---|
| Size, such as 3/4 IN or 1.25 IN | The nominal pipe size. It is a name, not a measurement. | Yes |
| SCH 40, SCH 80 or SCH 120 | The schedule, which sets the wall thickness. | Yes |
| PVC | The pipe is made of polyvinyl chloride. | No |
| PVC 1120 | The material designation for the PVC compound used to make the pipe. | No |
| ASTM D1785 | The standard for PVC pressure pipe in Schedules 40, 80 and 120. | No |
| Pressure rating in PSI, such as 480 PSI | The maximum water pressure rating at 73 degrees Fahrenheit. It is lower at higher temperatures and varies by size. | No |
| NSF-pw or NSF 61 | Certified for use with drinking water. | No |
| DWV | Drain, waste and vent pipe, which is not made for pressure. DWV pipe is usually marked ASTM D2665. | Check the schedule |
| Cellular core, foam core or ASTM F891 | Pipe with a foam center layer between a solid inner wall and a solid outer wall. It is lighter and costs less, but it is not ideal for structural PVC projects. Choose solid Schedule 40 pipe for furniture and other projects that carry weight. | Not recommended for structural projects |
| Manufacturer name, plant code and date code | Identifies who made the pipe and when. | No |
What If There Are No Markings?
Some pipe has no printing, or the marks have worn off. Measure the outside diameter and match it to a size chart. Wrap a flexible tape measure around the pipe and divide the circumference by 3.14, or hold a ruler across the end of the pipe.
If you can only measure the inside, Schedule 40 pipe has an inside diameter close to its size name, usually within about 1/8", so it works as a starting point. Confirm your size on the chart before you order.
PVC Markings FAQ
The size is printed along the side of the pipe, usually after the manufacturer name. It may be a fraction, such as 3/4 inch, or a decimal, such as 1.25 inches. Decimals are the same nominal sizes, so 1.25 inches is 1-1/4 inch pipe.
The printed size is a nominal size, which is a name and not a measurement. A pipe marked 3/4 inch has an outside diameter of 1.050 inches. This is true for every PVC pipe size. See the PVC Pipe Size Dimensions Chart for the outside diameter of each size.
SCH 40 means Schedule 40, which is the standard wall thickness for PVC pipe. Schedule 80 has a thicker wall and Schedule 120 has the thickest wall. The outside diameter is the same in every schedule, and a thicker wall means a smaller inside diameter.
ASTM D1785 is the standard for PVC pressure pipe in Schedules 40, 80 and 120. It tells you the pipe is made to a recognized specification for dimensions and pressure ratings. It does not affect how the pipe fits FORMUFIT products.
Yes. Plumbing-grade PVC pipe works with FORMUFIT fittings and accessories. Internal-fit products work only with Schedule 40 pipe. External-fit products work with Schedule 40, Schedule 80 and thinwall pipe.
Measure the outside diameter and match it to a size chart. Wrap a flexible tape measure around the pipe and divide the circumference by 3.14, or hold a ruler across the end of the pipe. You can also compare the pipe with everyday objects on the PVC Pipe Size Comparison Chart.
Keep Learning About PVC Pipe
Keep going with the printable size guide, the full PVC 101 overview, or the accessories guide.
Reviewed October 7, 2026 by FORMUFIT LC. Dimensions per ASTM D1785.