DN - NPS Conversion
& Pipe Schedule Table
DN to NPS conversion and pipe wall thickness values per ASME B36.10 standard.
Search & Convert DN / NPS
DN - NPS - OD & Schedule Table
| DN | NPS | OD (mm) | SCH 5 | SCH 10 | SCH 20 | SCH 30 | SCH 40 | SCH 60 | SCH 80 | SCH 100 | SCH 120 | SCH 140 | SCH 160 | STD | XS | XXS |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 15 | 1/2" | 21.3 | 1.65 | 2.11 | - | - | 2.77 | - | 3.73 | - | - | - | 4.78 | 2.77 | 3.73 | 7.47 |
| 20 | 3/4" | 26.7 | 1.65 | 2.11 | - | - | 2.87 | - | 3.91 | - | - | - | 5.56 | 2.87 | 3.91 | 7.82 |
| 25 | 1" | 33.4 | 1.65 | 2.77 | - | - | 3.38 | - | 4.55 | - | - | - | 6.35 | 3.38 | 4.55 | 9.09 |
| 32 | 1-1/4" | 42.2 | 1.65 | 2.77 | - | - | 3.56 | - | 4.85 | - | - | - | 6.35 | 3.56 | 4.85 | 9.70 |
| 40 | 1-1/2" | 48.3 | 1.65 | 2.77 | - | - | 3.68 | - | 5.08 | - | - | - | 7.14 | 3.68 | 5.08 | 10.15 |
| 50 | 2" | 60.3 | 1.65 | 2.77 | - | - | 3.91 | - | 5.54 | - | - | - | 8.74 | 3.91 | 5.54 | 11.07 |
| 65 | 2-1/2" | 73 | 2.11 | 3.05 | - | - | 5.16 | - | 7.01 | - | - | - | 9.53 | 5.16 | 7.01 | 14.02 |
| 80 | 3" | 88.9 | 2.11 | 3.05 | - | - | 5.49 | - | 7.62 | - | - | - | 11.13 | 5.49 | 7.62 | 15.24 |
| 100 | 4" | 114.3 | 2.77 | 3.05 | 3.96 | 4.78 | 6.02 | 7.14 | 8.56 | 11.13 | 13.49 | 15.88 | 17.12 | 6.02 | 8.56 | 17.12 |
| 125 | 5" | 141.3 | 2.77 | 3.40 | 5.56 | 6.55 | 6.55 | 9.53 | 9.53 | 12.70 | 15.88 | 18.26 | 19.05 | 6.55 | 9.53 | 19.05 |
| 150 | 6" | 168.3 | 2.77 | 3.40 | 5.56 | 6.35 | 7.11 | 10.97 | 10.97 | 14.27 | 18.26 | 21.95 | 21.95 | 7.11 | 10.97 | 21.95 |
| 200 | 8" | 219.1 | 2.77 | 3.76 | 6.35 | 7.04 | 8.18 | 10.31 | 12.70 | 15.09 | 18.26 | 20.62 | 23.01 | 8.18 | 12.70 | 22.23 |
| 250 | 10" | 273 | 3.40 | 4.19 | 6.35 | 7.80 | 9.27 | 12.70 | 12.70 | 18.26 | 21.44 | 25.40 | 28.58 | 9.27 | 12.70 | 28.58 |
| 300 | 12" | 323.8 | 3.96 | 4.57 | 6.35 | 8.38 | 9.53 | 12.70 | 12.70 | 21.44 | 25.40 | 28.58 | 33.32 | 9.53 | 12.70 | 33.32 |
| 350 | 14" | 355.6 | 3.96 | 4.78 | 7.92 | 9.53 | 11.13 | 15.09 | 19.05 | 23.83 | 27.79 | 31.75 | 35.71 | 9.53 | 12.70 | - |
| 400 | 16" | 406.4 | 4.19 | 4.78 | 7.92 | 9.53 | 12.70 | 16.66 | 21.44 | 26.19 | 30.96 | 36.53 | 40.49 | 9.53 | 12.70 | - |
| 450 | 18" | 457.2 | 4.19 | 4.78 | 7.92 | 11.13 | 14.27 | 19.05 | 23.83 | 29.36 | 34.93 | 39.67 | 45.24 | 9.53 | 12.70 | - |
| 500 | 20" | 508 | 4.78 | 5.54 | 9.53 | 12.70 | 15.09 | 20.62 | 26.19 | 32.54 | 38.10 | 44.45 | 50.01 | 9.53 | 12.70 | - |
| 600 | 24" | 609.6 | 5.54 | 6.35 | 9.53 | 14.27 | 17.48 | 24.61 | 30.96 | 38.89 | 46.02 | 52.37 | 59.54 | 9.53 | 12.70 | - |
* All values are in mm. Source: ASME B36.10M. Click a row to select it.
What are DN, NPS, and Schedule?
Nominal Diameter (Diametre Nominal)
DN is the metric designation used to describe pipe size. Expressed in millimeters, it does not directly represent the actual inner or outer diameter; it is an industrial reference number defined per ISO 6708.
Nominal Pipe Size
NPS is the imperial pipe sizing designation used in North America. Expressed in inches. For NPS 14 and above, NPS directly equals the OD in inches. For smaller sizes, it is a historical reference number.
Pipe Schedule
The schedule number defines the pipe wall thickness. Different schedule values for the same nominal size provide different wall thicknesses and pressure ratings. Per ASME B36.10, values from SCH 5 to SCH 160 are defined. STD, XS, and XXS are special designations.
Important Notes
- 1.STD (Standard) generally equals SCH 40 (up to DN 250). For larger sizes, STD wall thickness is fixed at 9.53 mm.
- 2.XS (Extra Strong) generally equals SCH 80 (up to DN 200). For larger sizes, XS wall thickness is fixed at 12.70 mm.
- 3.XXS (Double Extra Strong) is the heaviest standard pipe. XXS is not defined for DN 350 and above.
- 4.Outer diameter (OD) is constant for all schedules. As schedule increases, inner diameter decreases and pressure rating increases.
Pipe Weight Formula
Where W = Weight (kg/m), OD = Outer Diameter (mm), WT = Wall Thickness (mm)
Example Calculation:
DN100, SCH 40 pipe: OD = 114.3 mm, WT = 6.02 mm
W = (114.3 - 6.02) x 6.02 x 0.02466 = 16.07 kg/m
What is DN to NPS conversion?
DN (Diamètre Nominal, metric) and NPS (Nominal Pipe Size, inch) are standard designations for the nominal size of pipes and flanges. Conversion uses a standard table: NPS 1/2" = DN15, NPS 1" = DN25, NPS 2" = DN50, NPS 4" = DN100, NPS 6" = DN150. The key point: DN and NPS are dimensionless nominal values, not actual dimensions — the real outside diameter differs (e.g. an NPS 2"/DN50 pipe has a 60.3 mm outside diameter).
DN/NPS chart and logic
For pipes and pipe fittings (flanges, fittings), the size is given by a 'nominal size' rather than the real millimeters. In the European system this is DN (metric); in the American system it is NPS (inch). There is no single fixed multiplier between them; a standardized mapping table is used. Common mappings: • NPS 1/2" = DN15 · NPS 3/4" = DN20 · NPS 1" = DN25 • NPS 1½" = DN40 · NPS 2" = DN50 · NPS 3" = DN80 • NPS 4" = DN100 · NPS 6" = DN150 · NPS 8" = DN200 • NPS 10" = DN250 · NPS 12" = DN300 Critical distinction: DN 50 does NOT mean a 50 mm outside diameter; it is a nominal value. The real outside diameter of NPS 2"/DN50 pipe is 60.3 mm. The actual wall thickness is set by the Schedule (Sch 40, Sch 80...). That is why orders and assembly use DN/NPS + Schedule + PN/Class together.
Pipe size chart: DN / NPS, Schedule 40-80 wall thickness and kg/m
| DN | NPS | Outside Ø (mm) | Sch 40 wall (mm) | Sch 40 (kg/m) | Sch 80 wall (mm) | Sch 80 (kg/m) |
|---|---|---|---|---|---|---|
| DN15 | 1/2" | 21,3 | 2,77 | 1,27 | 3,73 | 1,62 |
| DN20 | 3/4" | 26,7 | 2,87 | 1,69 | 3,91 | 2,20 |
| DN25 | 1" | 33,4 | 3,38 | 2,50 | 4,55 | 3,24 |
| DN32 | 1¼" | 42,2 | 3,56 | 3,39 | 4,85 | 4,47 |
| DN40 | 1½" | 48,3 | 3,68 | 4,05 | 5,08 | 5,41 |
| DN50 | 2" | 60,3 | 3,91 | 5,44 | 5,54 | 7,48 |
| DN65 | 2½" | 73,0 | 5,16 | 8,63 | 7,01 | 11,41 |
| DN80 | 3" | 88,9 | 5,49 | 11,29 | 7,62 | 15,27 |
| DN100 | 4" | 114,3 | 6,02 | 16,07 | 8,56 | 22,32 |
| DN125 | 5" | 141,3 | 6,55 | 21,77 | 9,53 | 30,97 |
| DN150 | 6" | 168,3 | 7,11 | 28,26 | 10,97 | 42,56 |
| DN200 | 8" | 219,1 | 8,18 | 42,55 | 12,70 | 64,64 |
| DN250 | 10" | 273,0 | 9,27 | 60,29 | 12,70 | 81,52 |
| DN300 | 12" | 323,8 | 9,53 | 73,86 | 12,70 | 97,43 |
| DN350 | 14" | 355,6 | 11,13 | 94,55 | 19,05 | 158,10 |
| DN400 | 16" | 406,4 | 12,70 | 123,30 | 21,44 | 203,53 |
| DN450 | 18" | 457,2 | 14,27 | 155,87 | 23,83 | 254,67 |
| DN500 | 20" | 508,0 | 15,09 | 183,42 | 26,19 | 311,17 |
| DN600 | 24" | 609,6 | 17,48 | 255,24 | 30,96 | 441,78 |
Outside diameters and wall thicknesses follow ASME B36.10. Weights are calculated for carbon steel (ρ = 7.85 g/cm³) from weight ≈ 0.0247 × wall × (OD − wall); stainless runs about 2% heavier. Coating, lining and weld preparation are not included.
Frequently Asked Questions
What is DN50 in inches?+
DN50 corresponds to NPS 2". But this is a nominal value; the actual outside diameter of NPS 2"/DN50 pipe is 60.3 mm, not 50 mm.
Is there a formula between DN and NPS?+
There is no single fixed formula; a rough approximation is DN ≈ NPS × 25 (NPS 1"→DN25). The official conversion uses a standard mapping table, because at larger sizes the ratio is not exactly 25.
Is DN the real pipe diameter?+
No. DN (and NPS) is a dimensionless nominal value, not the physical outside diameter. The real OD is a separate standard value (e.g. DN100 = 114.3 mm OD); wall thickness is set by the Schedule.
What DN is an NPS 4" flange?+
NPS 4" = DN100. When selecting a flange, the pressure class (PN or ASME Class) and bolt pattern must match in addition to the nominal DN/NPS size.
How much does a DN150 Sch 40 pipe weigh?+
DN150 (NPS 6") has an outside diameter of 168.3 mm and a Sch 40 wall of 7.11 mm, giving roughly 28.3 kg/m. At Sch 80 the wall rises to 10.97 mm and the weight to 42.6 kg/m. Formula: weight (kg/m) ≈ 0.0247 × wall × (OD − wall).
What is the difference between Schedule 40 and Schedule 80?+
Schedule sets the wall thickness at a given outside diameter — the OD stays the same, the bore narrows. At DN150, Sch 40 is 7.11 mm and Sch 80 is 10.97 mm; weight goes from 28.3 to 42.6 kg/m. Sch 80 is chosen for higher pressure or a corrosion allowance. In small sizes Sch 40 equals STD and Sch 80 equals XS; from DN250 upwards that equivalence breaks down.
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