DN to Inches Conversion Table (Quick Answer)
The DN system of conversions simplifies these measurements by ignoring the demical point and rounding down to the nearest zero or five. Using the above example, 1 inch equals 33.40 milimetres but rendered as DN25; 8 inch equals 219.1 milimeters but rendered as DN200; while, a 14 inch flange will be termed as DN350.
|
DN |
Inch (NPS) |
OD (mm) |
OD (inch) |
|
DN6 |
1/8 |
10.3 |
0.405 |
|
DN8 |
1/4 |
13.7 |
0.540 |
|
DN10 |
3/8 |
17.1 |
0.675 |
|
DN15 |
1/2 |
21.3 |
0.840 |
|
DN20 |
3/4 |
26.7 |
1.050 |
|
DN25 |
1 |
33.4 |
1.315 |
|
DN32 |
1-1/4 |
42.2 |
1.660 |
|
DN40 |
1-1/2 |
48.3 |
1.900 |
|
DN50 |
2 |
60.3 |
2.375 |
|
DN65 |
2-1/2 |
73.0 |
2.875 |
|
DN80 |
3 |
88.9 |
3.500 |
|
DN90 |
3-1/2 |
101.6 |
4.000 |
|
DN100 |
4 |
114.3 |
4.500 |
|
DN125 |
5 |
141.3 |
5.563 |
|
DN150 |
6 |
168.3 |
6.625 |
|
DN200 |
8 |
219.1 |
8.625 |
|
DN250 |
10 |
273.0 |
10.750 |
|
DN300 |
12 |
323.8 |
12.750 |
|
DN350 |
14 |
355.6 |
14.000 |
|
DN400 |
16 |
406.4 |
16.000 |
|
DN450 |
18 |
457.0 |
18.000 |
|
DN500 |
20 |
508.0 |
20.000 |
|
DN550 |
22 |
559.0 |
22.000 |
|
DN600 |
24 |
610.0 |
24.000 |
|
DN650 |
26 |
660.0 |
26.000 |
|
DN700 |
28 |
711.0 |
28.000 |
|
DN750 |
30 |
762.0 |
30.000 |
|
DN800 |
32 |
813.0 |
32.000 |
|
DN850 |
34 |
864.0 |
34.000 |
|
DN900 |
36 |
914.0 |
36.000 |
|
DN1000 |
40 |
1016.0 |
40.000 |
|
DN1050 |
42 |
1067.0 |
42.000 |
|
DN1100 |
44 |
1118.0 |
44.000 |
|
DN1200 |
48 |
1219.0 |
48.000 |
|
DN1400 |
56 |
1422.0 |
56.000 |
|
DN1500 |
60 |
1524.0 |
60.000 |
|
DN1600 |
64 |
1626.0 |
64.000 |
|
DN1800 |
72 |
1829.0 |
72.000 |
|
DN2000 |
80 |
2032.0 |
80.000 |
|
DN2400 |
96 |
2438.0 |
96.000 |
|
DN3000 |
120 |
3048.0 |
120.000 |
Note: OD values above follow ASME B36.10M / B36.19M (NPS system). European metric pipe to EN 10255 uses different outside diameters for the same DN - for example DN65 is 76.1 mm OD in EN 10255 but 73.0 mm OD in ASME B36.10M. Always confirm which system your project specifies.
Download the full DN to Inch Chart (PDF) - DN6 to DN3000 with OD and wall thickness
How to convert DN to inches
DN (Diamètre Nominal) is a metric nominal diameter. NPS (Nominal Pipe Size) is the inch equivalent used in ASME standards. They are not a direct millimetre-to-inch conversion - a DN25 pipe has a 33.4 mm outside diameter, not 25 mm.
The conversion works by rounding: NPS 1 = 1 inch = 25.4 mm nominal, which is expressed as DN25. NPS 8 = 8 inch, expressed as DN200.
To convert any DN value to inches: divide the DN number by 25 and round to the nearest standard NPS size, then check the chart above for the actual outside diameter.
DN To Inches Chart
| Diameter Nominal DN (mm) | Nominal Pipe Size (inches) | Outside diameter (OD) inches (mm) |
|---|---|---|
| 6 | 1⁄8 | 0.405 in (10.29 mm) |
| 8 | 1⁄4 | 0.540 in (13.72 mm) |
| 10 | ⅜ | 0.675 in (17.15 mm) |
| 15 | ½ | 0.840 in (21.34 mm) |
| 20 | ¾ | 1.050 in (26.67 mm) |
| 25 | 1 | 1.315 in (33.40 mm) |
| 32 | 1 1⁄4 | 1.660 in (42.16 mm) |
| 40 | 1 ½ | 1.900 in (48.26 mm) |
| 50 | 2 | 2.375 in (60.33 mm) |
| 65 | 2 ½ | 2.875 in (73.02 mm) |
| 80 | 3 | 3.500 in (88.90 mm) |
| 100 | 4 | 4.500 in (114.30 mm) |
| 150 | 6 | 6.625 in (168.27 mm) |
| 200 | 8 | 8.625 in (219.08 mm) |
| 250 | 10 | 10.75 in (273.05 mm |
| DN | NPS | DN | NPS | DN | NPS |
| (Diameter Nominal) | (Nominal Pipe Size) | (Diameter Nominal) | (Nominal Pipe Size) | (Diameter Nominal) | (Nominal Pipe Size) |
| Milimeters | Inches | Milimeters | Inches | Milimeters | Inches |
| 100 | 4 | 700 | 28 | 1800 | 72 |
| 115 | 4 1/2 | 800 | 32 | 1900 | 76 |
| 125 | 5 | 900 | 36 | 2000 | 80 |
| 150 | 6 | 1000 | 40 | 2200 | 88 |
| 200 | 8 | 1050 | 42 | 2400 | 96 |
| 250 | 10 | 1100 | 44 | 2600 | 104 |
| 300 | 12 | 1200 | 48 | 2800 | 112 |
| 350 | 14 | 1300 | 52 | 3000 | 120 |
| 400 | 16 | 1400 | 56 | 3200 | 128 |
| 450 | 18 | 1500 | 60 | 3400 | 134 |
| 500 | 20 | 1600 | 64 | 3600 | 142 |
| 600 | 24 | 1700 | 68 | 3800 | 150 |
Diameters in DN or in NPS
From within the industrial market we find these two systems to size the diameters for pipes, tubes, valve connections and other devices:
- Nominal pipe size (NPS) , defined by the American standard ANSI / ASME B36.19 is based on inches .
- Nominal diameter (DN) , defined by the European standard ISO 6708 is based on millimeters. Diameter Nominale, is a non-precise conversion of Imperial Units to Metric Units.
We know that to determine the conversion operation from one value to another, we should only perform a simple simple mathematical formula (the value of a inch is 25.4 millimeters and that of 1 millimeter 0.0393701 inches); however we could not apply it to determine these values because each system uses a commercial measure that does not correspond with the real value of the outside diameter of the pipe but with the inside of it. We observe a difference of 0.4 millimeters in the value DN 25 while in larger sizes the difference is even greater , for example: 120 inches is actually 3048 millimeters, 48 millimeters more than the DN 3000 value.
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FAQ
What is DN25 in inches?
DN25 equals 1 inch (NPS 1). Its outside diameter is 33.4 mm or 1.315 inch. DN25 is the most commonly requested size for stainless steel pipe and fittings.
What is DN20 in inches?
DN20 equals 3/4 inch (NPS 3/4). Its outside diameter is 26.7 mm or 1.050 inch.
What is DN50 in inches?
DN50 equals 2 inch (NPS 2). Its outside diameter is 60.3 mm or 2.375 inch. DN50 is common in general process piping and water lines.
Is DN the same as the outside diameter?
No. DN is a nominal reference number and is not a measurable dimension. DN50 pipe has a 60.3 mm outside diameter, not 50 mm. Always use the OD column in the chart above for dimensional work.
What is the difference between DN and NPS?
DN is the metric designation used in ISO and EN standards. NPS is the inch designation used in ASME B36.10M and B36.19M. For most sizes above DN6 they refer to the same pipe, but the actual outside diameter follows the NPS value, not the DN number.
