Pipe Schedule Chart: OD, Wall Thickness, and Weight for Common NPS Sizes

Nominal pipe size (NPS) is one of the most confusing measurement systems in construction. A "2-inch pipe" does not have a 2-inch outer diameter. It has a 2.375-inch OD — a number that seems arbitrary until you understand that it is standardized across all schedules of that size, and that the schedule number determines only the wall thickness (and therefore the ID and weight).

This guide explains the system and provides the complete reference data for Schedule 40 and Schedule 80 carbon steel pipe per ANSI/ASME B36.10M. For weight calculations by length, use our .

How the NPS system works

NPS (Nominal Pipe Size) is a North American designation. For sizes NPS 1/8" through NPS 12", the nominal size is not the actual OD. Instead:

• All schedules of the same NPS have the same OD
• The schedule number determines wall thickness
• The inside diameter changes with schedule because the OD is fixed and wall thickness varies

For NPS 14" and above, the nominal size equals the actual OD in inches.

Common schedule designations

Schedule	Common name	Primary use
Sch 10	—	Low-pressure, thin wall
Sch 40	Standard (STD)	Most common; residential plumbing, general industrial
Sch 80	Extra Strong (XS)	Higher pressure; industrial, chemical
Sch 160	—	High pressure
Sch XXS	Double Extra Strong	Extreme pressure

Schedule 40 pipe: complete reference

NPS	OD (in)	Wall (in)	ID (in)	Lbs/ft
1/8"	0.405	0.068	0.269	0.245
1/4"	0.540	0.088	0.364	0.425
3/8"	0.675	0.091	0.493	0.568
1/2"	0.840	0.109	0.622	0.851
3/4"	1.050	0.113	0.824	1.131
1"	1.315	0.133	1.049	1.678
1-1/4"	1.660	0.140	1.380	2.272
1-1/2"	1.900	0.145	1.610	2.717
2"	2.375	0.154	2.067	3.653
2-1/2"	2.875	0.203	2.469	5.793
3"	3.500	0.216	3.068	7.576
4"	4.500	0.237	4.026	10.79
6"	6.625	0.280	6.065	18.97
8"	8.625	0.322	7.981	28.55
10"	10.750	0.365	10.020	40.48
12"	12.750	0.406	11.938	53.52

Schedule 80 pipe: reference

NPS	OD (in)	Wall (in)	ID (in)	Lbs/ft
1/2"	0.840	0.147	0.546	1.087
3/4"	1.050	0.154	0.742	1.473
1"	1.315	0.179	0.957	2.172
1-1/2"	1.900	0.200	1.500	3.631
2"	2.375	0.218	1.939	5.022
3"	3.500	0.300	2.900	10.25
4"	4.500	0.337	3.826	14.98
6"	6.625	0.432	5.761	28.57

Calculating pipe weight

The weight per foot formula for any hollow round section:

W = 10.69 x (OD - wall) x wall

Where OD and wall are in inches, result is pounds per foot for carbon steel.

Example: NPS 4" Schedule 40

W = 10.69 x (4.500 - 0.237) x 0.237 = 10.69 x 4.263 x 0.237 = 10.79 lbs/ft

For a 20-ft run: 10.79 x 20 = 215.8 lbs

Pipe material weight adjustments

The formula above is for carbon steel. For other materials, multiply by the density ratio:

Material	Multiply carbon steel weight by
Carbon steel	1.00 (reference)
304 Stainless steel	1.02
316 Stainless steel	1.02
Aluminum 6061	0.35
Copper	1.14
PVC (Schedule 40)	~0.22

A 4-inch Schedule 40 aluminum pipe (10.79 x 0.35 = 3.78 lbs/ft) weighs about one-third as much as the equivalent steel pipe — significant for overhead applications and structural weight calculations.

For any pipe size, schedule, material, and length, the  looks up the ANSI/ASME data and converts to your preferred weight unit.