Common Pipe Dimensions: Nominal Size, OD and ID
A pipe’s nominal size is a name, not a measurement: every pipe of one nominal size has the same outside diameter, and the wall thickness (its schedule) sets the inside diameter. A 1 in pipe is 1.315 in across the outside.
Steel pipe, NPS 1/8 to 6
| NPS | DN | Outside diameter | Schedule 40 inside | Schedule 80 inside |
|---|---|---|---|---|
| 1/8 | 6 | 0.405 in (10.3 mm) | 0.269 in (6.8 mm) | 0.215 in (5.5 mm) |
| 1/4 | 8 | 0.540 in (13.7 mm) | 0.364 in (9.2 mm) | 0.302 in (7.7 mm) |
| 3/8 | 10 | 0.675 in (17.1 mm) | 0.493 in (12.5 mm) | 0.423 in (10.7 mm) |
| 1/2 | 15 | 0.840 in (21.3 mm) | 0.622 in (15.8 mm) | 0.546 in (13.9 mm) |
| 3/4 | 20 | 1.050 in (26.7 mm) | 0.824 in (20.9 mm) | 0.742 in (18.8 mm) |
| 1 | 25 | 1.315 in (33.4 mm) | 1.049 in (26.6 mm) | 0.957 in (24.3 mm) |
| 1 1/4 | 32 | 1.660 in (42.2 mm) | 1.380 in (35.1 mm) | 1.278 in (32.5 mm) |
| 1 1/2 | 40 | 1.900 in (48.3 mm) | 1.610 in (40.9 mm) | 1.500 in (38.1 mm) |
| 2 | 50 | 2.375 in (60.3 mm) | 2.067 in (52.5 mm) | 1.939 in (49.3 mm) |
| 2 1/2 | 65 | 2.875 in (73.0 mm) | 2.469 in (62.7 mm) | 2.323 in (59.0 mm) |
| 3 | 80 | 3.500 in (88.9 mm) | 3.068 in (77.9 mm) | 2.900 in (73.7 mm) |
| 4 | 100 | 4.500 in (114.3 mm) | 4.026 in (102.3 mm) | 3.826 in (97.2 mm) |
| 5 | 125 | 5.563 in (141.3 mm) | 5.047 in (128.2 mm) | 4.813 in (122.3 mm) |
| 6 | 150 | 6.625 in (168.3 mm) | 6.065 in (154.1 mm) | 5.761 in (146.3 mm) |
Reading the table
- NPS is the North American nominal size; DN is the metric equivalent used in Europe and elsewhere for the same outside diameters.
- Schedule 40 is standard wall; Schedule 80 is thicker for higher pressures, so its inside diameter is smaller.
- PVC Schedule 40 and 80 pipe shares these outside diameters. Copper tube and PEX use different sizing (copper’s outside diameter is 1/8 in larger than its nominal size).
Use the inside diameter in the pipe volume calculator, the flow rate calculator and the water velocity calculator.
Source
- ASME B36.10M, Welded and Seamless Wrought Steel Pipe (outside diameters and wall thicknesses by schedule).