NPS (Nominal Pipe Size) is a dimensionless ordinal number used to represent pipe size. A number after it indicates a standard pipe. For example: the outer diameter of steel pipes represented by NPS 6 is uniformly 168.3mm.
DN: Normal Diameter
ASME B36.10/36.19 NPS to DN Conversion Chart
| PIPE NPS | Pipe outside diameter in inches |
PIpe outside diameter in mm |
NPS to DN conversion |
|---|---|---|---|
| 1/8 | 0.404 | 10.26 | 6 |
| 1/4 | 0.54 | 13.72 | 8 |
| 3/8 | 0.675 | 17.15 | 10 |
| 1/2 | 0.84 | 21.34 | 15 |
| ¾ | 1.05 | 26.67 | 20 |
| 1 | 1.315 | 33.40 | 25 |
| 1 ¼ | 1.66 | 42.16 | 32 |
| 1 ½ | 1.9 | 48.26 | 40 |
| 2 | 2.375 | 60.33 | 50 |
| 2 ½ | 2.875 | 73.03 | 65 |
| 3 | 3.5 | 88.90 | 80 |
| 3 ½ | 4 | 101.60 | 90 |
| 4 | 4.5 | 114.30 | 100 |
| 4 ½ | 5 | 127.00 | 115 |
| 5 | 5.563 | 141.30 | 125 |
| 6 | 6.625 | 168.28 | 150 |
| 7 | 7.625 | 193.68 | - |
| 8 | 8.625 | 219.08 | 200 |
| 10 | 10.75 | 273.05 | 250 |
| 12 | 12.75 | 323.85 | 300 |
| 14 | 14 | 355.60 | 350 |
| 16 | 16 | 406.40 | 400 |
| 18 | 18 | 457.20 | 450 |
| 20 | 20 | 508.00 | 500 |
| 22 | 22 | 558.80 | 550 |
| 24 | 24 | 609.60 | 600 |
| 26 | 26 | 660.40 | 650 |
| 28 | 28 | 711.20 | 700 |
| 30 | 30 | 762.00 | 750 |
| 32 | 32 | 812.80 | 800 |
| 34 | 34 | 863.60 | 850 |
| 36 | 36 | 914.40 | 900 |
| 38 | 38 | 965.20 | 950 |
| 40 | 40 | 1016.00 | 1000 |
| 42 | 42 | 1066.80 | 1050 |
| 44 | 44 | 1117.60 | 1100 |
| 46 | 46 | 1168.40 | 1150 |
| 48 | 48 | 1219.20 | 120 |
Critical Engineering Insights for NPS vs. DN
NPS 1/8 to NPS 12 (OD vs. Nominal Size): For pipe sizes below 14 inches, the outer diameter (OD) is numerically larger than the stated nominal size. For instance, an NPS 2 pipe (DN 50) has an outer diameter of 2.375 inches (60.33 mm), not 2.000 inches.
NPS 14 and Larger: For pipe sizes 14 inches and above, the NPS numerical value directly equals the outer diameter in inches (e.g., NPS 24 has an exact OD of 24.000 inches / 609.60 mm).
DN Designation Equivalency: The metric DN value is a rounded reference number under EN ISO 6708 and ASME standards. It roughly corresponds to the internal bore in millimeters for standard schedule pipes, but exact ID varies based on wall thickness.
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FAQ
Question: What is the difference between ASME B36.10 and ASME B36.19?
Answer: ASME B36.10M covers carbon steel and alloy steel pipes across various schedules, whereas ASME B36.19M specifically covers stainless steel, duplex, and nickel alloy pipes with standard schedules denoted by an 'S' suffix (e.g., SCH 10S, SCH 40S).
Question: What is NPS 2 in metric DN size?
Answer: NPS 2 corresponds to DN 50 in metric size, with an outside diameter (OD) of 2.375 inches (60.33 mm).
Question: Does Nominal Pipe Size (NPS) equal the outer diameter (OD)?
Answer: For pipe sizes under NPS 14, the NPS value does not equal the outer diameter. For NPS 14 and larger, the NPS designation directly equals the pipe outer diameter in inches.
