NPS to OD Reference Table

A lookup table for nominal pipe size to true outside diameter, under ASME B36.10 / B36.19. Outside diameter is fixed per NPS regardless of schedule or wall thickness, so this table applies no matter what wall thickness a project uses. Use it to convert an NPS callout into the true OD value the other calculators in this suite expect.

Section 1

Find a size

Filter by NPS or OD

Matches against the NPS label or either OD column. Clear the box to see the full table.

Section 2

NPS to true outside diameter

Outside diameter is fixed per NPS regardless of schedule or wall thickness. ASME B36.10 / B36.19 nominal pipe sizes, 1/8 inch through 60 inch.
NPS	OD (in)	OD (mm)
1/8	0.405	10.3
1/4	0.540	13.7
3/8	0.675	17.1
1/2	0.840	21.3
3/4	1.050	26.7
1	1.315	33.4
1-1/4	1.660	42.2
1-1/2	1.900	48.3
2	2.375	60.3
2-1/2	2.875	73.0
3	3.500	88.9
3-1/2	4.0	101.6
4	4.500	114.3
5	5.563	141.3
6	6.625	168.3
8	8.625	219.1
10	10.750	273.1
12	12.750	323.9
14	14.0	355.6
16	16.0	406.4
18	18.0	457.2
20	20.0	508.0
22	22.0	558.8
24	24.0	609.6
26	26.0	660.4
28	28.0	711.2
30	30.0	762.0
32	32.0	812.8
34	34.0	863.6
36	36.0	914.4
38	38.0	965.2
40	40.0	1,016.0
42	42.0	1,066.8
44	44.0	1,117.6
46	46.0	1,168.4
48	48.0	1,219.2
54	54.0	1,371.6
60	60.0	1,524.0

What this table covers

Nominal pipe size, or NPS, is a naming convention, not a physical measurement. For NPS 1/8 through NPS 12, the NPS number does not equal the true outside diameter. Starting at NPS 14, the NPS number equals the true outside diameter in inches exactly. This table lists the true OD for every standard NPS from 1/8 inch through 60 inch, in both inches and millimetres.

This page lists outside diameter only. It does not include a schedule-by-schedule wall thickness chart, since wall thickness varies by schedule and by manufacturer, and larger transmission pipe is commonly specified by wall thickness directly rather than by a schedule number. Confirm wall thickness against project specifications or the current edition of ASME B36.10 / B36.19.