Pipe size chart (DN to inch)
DN15 to DN300: the inch equivalent, outside diameter, common wall, weight per metre and external area for insulation take-off.
| DN | Inch | Outside dia (mm) | Wall (mm) | Weight (kg/m) | Area (m²/m) |
|---|---|---|---|---|---|
| DN15 | 1/2" | 21.3 | 2.8 | 1.28 | 0.067 |
| DN20 | 3/4" | 26.9 | 2.8 | 1.66 | 0.085 |
| DN25 | 1" | 33.7 | 3.2 | 2.41 | 0.106 |
| DN32 | 1¼" | 42.4 | 3.5 | 3.36 | 0.133 |
| DN40 | 1½" | 48.3 | 3.5 | 3.87 | 0.152 |
| DN50 | 2" | 60.3 | 3.8 | 5.29 | 0.189 |
| DN65 | 2½" | 76.1 | 4.0 | 7.11 | 0.239 |
| DN80 | 3" | 88.9 | 4.0 | 8.37 | 0.279 |
| DN100 | 4" | 114.3 | 4.0 | 10.88 | 0.359 |
| DN125 | 5" | 139.7 | 4.0 | 13.39 | 0.439 |
| DN150 | 6" | 168.3 | 4.5 | 18.18 | 0.529 |
| DN200 | 8" | 219.1 | 6.0 | 31.53 | 0.688 |
| DN250 | 10" | 273.0 | 6.5 | 42.72 | 0.858 |
| DN300 | 12" | 323.9 | 7.9 | 61.56 | 1.018 |
All values are computed from the stated formulas; ranges show the usual spread. Use measured data or the local code where it differs.
How to use this table
- A drawing calling DN50 means a 2 inch pipe, 60.3 mm outside diameter, with 2 inch flanges and valves.
- For insulation, multiply the external area by thickness and insulation density.
- For supports, look up the maximum spacing for that diameter — 6 m is typical above DN100.
Common misuse
- Treating DN as the outside diameter — DN50 is 60.3 mm outside, and a 10 mm error will not fit.
- Reading DN as a decimal inch — 1 inch is 25.4 mm, but 1 inch pipe is 33.7 mm outside because DN is sized on the bore series.
- Using plain steel wall thickness for galvanised pipe — the zinc adds 3-5% to the weight.
Calculate the actual number
Other reference tables
FAQ
What is DN50 in inches?
Two inch, 60.3 mm outside diameter, commonly 3.8 mm wall, 5.29 kg per metre.
What is the outside diameter of DN25?
33.7 mm, which is 1 inch. Note the outside diameter is 8.7 mm larger than the DN, so fittings are selected on outside diameter.
What is the difference between DN, De and Φ?
DN is a nominal size close to the bore but not exact; De is the outside diameter of plastic pipe; Φ usually means outside diameter × wall thickness. They are not interchangeable.
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.