Steel Pipe Sizes (NPS and DN, Schedule 40 and 80)

Nominal pipe size (NPS and DN) with outside and inside diameter, wall, flow area and mass for Schedule 40 and 80.

Steel pipe is sized by nominal pipe size: NPS in inches in North America, DN (diameter nominal, in millimeters) elsewhere. The nominal size is a name, not a measurement: a 2-inch pipe has an outside diameter of 60.33 mm, not 50.8 mm. The schedule sets the wall thickness, and so the inside diameter.

This table lists NPS ½ to 12 in Schedule 40 and Schedule 80, with the inside diameter, flow area and steel mass worked out from the outside diameter and wall.

The table

28 rows

Nominal size	DN	Schedule	Outside diameter (mm)	Wall (mm)	Inside diameter (mm)	Flow area (cm2)	Steel mass (kg/m)
NPS 1/2	15	Sch 40	21.34	2.77	15.8	1.961	1.27
NPS 1/2	15	Sch 80	21.34	3.73	13.88	1.513	1.62
NPS 3/4	20	Sch 40	26.67	2.87	20.93	3.441	1.68
NPS 3/4	20	Sch 80	26.67	3.91	18.85	2.791	2.19
NPS 1	25	Sch 40	33.4	3.38	26.64	5.574	2.5
NPS 1	25	Sch 80	33.4	4.55	24.3	4.638	3.24
NPS 1-1/4	32	Sch 40	42.16	3.56	35.04	9.643	3.39
NPS 1-1/4	32	Sch 80	42.16	4.85	32.46	8.275	4.46
NPS 1-1/2	40	Sch 40	48.26	3.68	40.9	13.138	4.05
NPS 1-1/2	40	Sch 80	48.26	5.08	38.1	11.401	5.41
NPS 2	50	Sch 40	60.33	3.91	52.51	21.656	5.44
NPS 2	50	Sch 80	60.33	5.54	49.25	19.05	7.49
NPS 2-1/2	65	Sch 40	73.03	5.16	62.71	30.886	8.64
NPS 2-1/2	65	Sch 80	73.03	7.01	59.01	27.349	11.41
NPS 3	80	Sch 40	88.9	5.49	77.92	47.686	11.29
NPS 3	80	Sch 80	88.9	7.62	73.66	42.614	15.27
NPS 4	100	Sch 40	114.3	6.02	102.26	82.13	16.08
NPS 4	100	Sch 80	114.3	8.56	97.18	74.173	22.32
NPS 5	125	Sch 40	141.3	6.55	128.2	129.082	21.77
NPS 5	125	Sch 80	141.3	9.53	122.24	117.359	30.97
NPS 6	150	Sch 40	168.28	7.11	154.06	186.41	28.26
NPS 6	150	Sch 80	168.28	10.97	146.34	168.196	42.56
NPS 8	200	Sch 40	219.08	8.18	202.72	322.763	42.55
NPS 8	200	Sch 80	219.08	12.7	193.68	294.618	64.64
NPS 10	250	Sch 40	273.05	9.27	254.51	508.744	60.3
NPS 10	250	Sch 80	273.05	15.09	242.87	463.274	96
NPS 12	300	Sch 40	323.85	9.53	304.79	729.611	73.87
NPS 12	300	Sch 80	323.85	17.48	288.89	655.473	132.07

Source and notes: ASME B36.10M (carbon steel pipe), B36.19M for stainless. Inside diameter, flow area and mass (7 850 kg/m3) are computed from the OD and wall.

How to use this table

Find the nominal size and schedule (the filter box helps: type “2” or “Sch 80”).
Use the inside diameter and flow area for flow and pressure drop calculations, never the nominal size.
Use the mass per meter to estimate the weight and the support loads of a pipe run (add the weight of the contents).

Worked example: water in 2-inch Schedule 40 pipe at 2 m/s

Outside diameter 60.33 mm, wall 3.91 mm, so the inside diameter is 52.51 mm and the flow area 21.656 cm².
Flow = area × velocity = 0.002166 m² × 2 m/s = 4.33 L/s = 15.6 m³/h (69 US gpm).
The pipe itself weighs 5.44 kg per meter.

Notes and cautions

For NPS 14 and larger the nominal size equals the outside diameter. For NPS 12 and smaller it does not.
Schedule 40 and 80 are the two most common; other schedules (10, 20, 160, XXS) and stainless “S” schedules have different walls. Check B36.10M and B36.19M.
Mass assumes carbon steel at 7 850 kg/m³. Stainless steel is about 2 percent heavier.

FAQ

Why is a 2-inch pipe not 2 inches across?

The nominal size is a historical name from when pipe wall thickness was a single standard. Outside diameters were fixed for each size, so the name stayed while the walls changed.

What is the difference between Schedule 40 and Schedule 80?

Schedule 80 has a thicker wall for the same outside diameter. It carries a higher pressure, weighs more and has a smaller bore.

What is DN?

DN is the metric nominal size, a rounded number in millimeters: DN 50 corresponds to NPS 2.

Sources

ASME B36.10M (welded and seamless wrought steel pipe); ASME B36.19M (stainless steel pipe).
ASME B36.10M (carbon steel pipe), B36.19M for stainless. Inside diameter, flow area and mass (7 850 kg/m3) are computed from the OD and wall.