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.
- Selecting fittings: DN is a nominal size, not an outside diameter. DN50 welded steel pipe is 60.3 mm OD while PPR is 63 mm, so flanges must be ordered on actual OD.
- Flow: bore = OD − 2 × wall thickness. Set velocity at 1.0-1.5 m/s for domestic supply and back out the flow.
- Insulation: the insulation bore follows the pipe OD, so DN50 steel pipe (60.3 mm) needs 63 or 76 mm bore insulation, not 50.
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.
- Ordering to DN as if it were outside diameter. DN50 steel pipe is 60.3 mm OD, so flanges and clamps bought as 50 mm will not fit — the most common rework cause in pipework.
- Computing area from DN. DN100 steel pipe is 114.3 mm OD, giving a 106 mm bore at 4 mm wall; using 100 mm underestimates the area by 11%, and flow and velocity follow it.
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.
How does DN map to inches?
DN15 = 1/2", DN20 = 3/4", DN25 = 1", DN32 = 1-1/4", DN40 = 1-1/2", DN50 = 2", DN65 = 2-1/2", DN80 = 3", DN100 = 4", DN150 = 6". These are imperial inches, not the Chinese cun.
What is the outside diameter of DN100 pipe?
Welded steel pipe DN100 is 114.3 mm OD; seamless is commonly Φ108. Bore depends on wall: SCH40 at 6.02 mm gives 102.3 mm, SCH80 at 8.56 mm gives 97.2 mm.
Why is PPR marked De rather than DN?
Plastic pipe is designated by outside diameter because wall thickness varies with pressure class while OD stays stable. Equivalents: De25 = DN20, De32 = DN25, De40 = DN32, De50 = DN40, De63 = DN50 and De110 = DN100.
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.