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NPS · NB · DN · OD (mm & inch)

Pipe Size Chart — NB, DN & OD

Convert nominal pipe size (NPS) to nominal bore (NB), DN and outside diameter (OD) in millimetres and inches. Covers 1/8" (DN6) to 48" (DN1200).

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/ Overview

Nominal size vs actual outside diameter

Pipe is specified by nominal size — NPS (inch), NB (nominal bore) or DN (metric) — which is a label, not the true diameter. The actual outside diameter (OD) is fixed for each nominal size regardless of wall thickness/schedule, so fittings and flanges match. Use the chart below to convert between NPS, NB, DN and OD.

/ Size chart

NPS / NB / DN / OD conversion

NPS (inch)NB / DNOD (mm)OD (inch)
1/8″DN610.30.406
1/4″DN813.70.539
3/8″DN1017.10.673
1/2″DN1521.30.839
3/4″DN2026.71.051
1″DN2533.41.315
1 1/4″DN3242.21.661
1 1/2″DN4048.31.902
2″DN5060.32.374
2 1/2″DN6573.02.874
3″DN8088.93.5
3 1/2″DN90101.64.0
4″DN100114.34.5
5″DN125141.35.563
6″DN150168.36.626
8″DN200219.18.626
10″DN250273.010.748
12″DN300323.812.748
14″DN350355.614.0
16″DN400406.416.0
18″DN450457.017.992
20″DN500508.020.0
22″DN550559.022.008
24″DN600610.024.016
26″DN650660.025.984
28″DN700711.027.992
30″DN750762.030.0
32″DN800813.032.008
34″DN850864.034.016
36″DN900914.035.984
42″DN10501066.842.0
48″DN12001219.248.0

OD is constant per nominal size; only the wall (schedule) changes. For wall thicknesses see the pipe schedule chart.

/ FAQ

Common questions

What is 80 NB in inches?
80 NB (DN80) equals 3 inch nominal pipe size (NPS 3), with an outside diameter of 88.9 mm.
What is the difference between NB, DN and NPS?
They are three labelling systems for the same nominal size: NB (nominal bore) and NPS (nominal pipe size, inch) are used in imperial practice, DN (diamètre nominal) is the metric equivalent. DN = NB in mm; e.g. NPS 2 = NB 50 = DN50.
What is the OD of a 2 inch pipe?
A 2 inch (NPS 2, DN50) pipe has a fixed outside diameter of 60.3 mm (2.375 inch), whatever the schedule.
Does pipe OD change with schedule?
No. The OD is constant for a given nominal size; increasing the schedule increases wall thickness and reduces the internal diameter, not the OD.
/ Related
Pipe Schedule ChartDimensions & WeightWeight CalculatorCarbon Steel PipeAll Resources
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