NPS to DN conversion chart
Nominal pipe size (NPS, inches) to diamètre nominal (DN, mm) conversion with the actual outside diameter of steel pipe.
| NPS (inch) | DN (mm) | OD (mm) | OD (inch) |
|---|---|---|---|
| 1/8" | 6 | 10.3 | 0.406 |
| 1/4" | 8 | 13.7 | 0.539 |
| 3/8" | 10 | 17.1 | 0.673 |
| 1/2" | 15 | 21.3 | 0.839 |
| 3/4" | 20 | 26.7 | 1.051 |
| 1" | 25 | 33.4 | 1.315 |
| 1-1/4" | 32 | 42.2 | 1.661 |
| 1-1/2" | 40 | 48.3 | 1.902 |
| 2" | 50 | 60.3 | 2.374 |
| 2-1/2" | 65 | 73.0 | 2.874 |
| 3" | 80 | 88.9 | 3.500 |
| 3-1/2" | 90 | 101.6 | 4.000 |
| 4" | 100 | 114.3 | 4.500 |
| 5" | 125 | 141.3 | 5.563 |
| 6" | 150 | 168.3 | 6.626 |
| 8" | 200 | 219.1 | 8.626 |
| 10" | 250 | 273.1 | 10.752 |
| 12" | 300 | 323.9 | 12.752 |
| 14" | 350 | 355.6 | 14.000 |
| 16" | 400 | 406.4 | 16.000 |
| 18" | 450 | 457.0 | 17.992 |
| 20" | 500 | 508.0 | 20.000 |
| 24" | 600 | 610.0 | 24.016 |
| 26" | 650 | 660.0 | 25.984 |
| 28" | 700 | 711.0 | 27.992 |
| 30" | 750 | 762.0 | 30.000 |
| 32" | 800 | 813.0 | 32.008 |
| 34" | 850 | 864.0 | 34.016 |
| 36" | 900 | 914.0 | 35.984 |
| 42" | 1050 | 1067.0 | 42.008 |
| 48" | 1200 | 1219.0 | 47.992 |
Frequently asked questions
What is DN 100 in inches?
DN 100 is NPS 4, with an outside diameter of 114.3 mm.
Is DN the same as the pipe outside diameter?
No. DN is a nominal designation. A DN 50 pipe has an OD of 60.3 mm.
Last updated 2026-11-02