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Standard Pipe Dimensions: NPS & Schedules

Reference guide for ASTM A53 Steel Pipes. Compares NPS (Nominal Pipe Size) with actual Outer Diameter (OD). Includes Wall Thickness and Weight for Schedule 40 and Schedule 80.

OD ID Wall

Diagram Legend

Outer Diameter (Actual)
Inner Diameter (Flow)
Wall Thickness
NPS Nominal Size OD Outer Dia (in) Schedule 40 (Std) Schedule 80 (X-Heavy) Metric OD mm
Wall (in) Weight (lbs/ft) Wall (in) Weight (lbs/ft)
1/4" 0.540 0.088 0.43 0.119 0.54 13.5
3/8" 0.675 0.091 0.57 0.126 0.74 17
1/2" 0.840 0.109 0.85 0.147 1.09 21.3
3/4" 1.050 0.113 1.13 0.154 1.48 26.8
1" 1.315 0.133 1.68 0.179 2.17 33.5
1 1/4" 1.660 0.140 2.27 0.191 3.00 42.3
1 1/2" 1.900 0.145 2.72 0.200 3.63 48
2" 2.375 0.154 3.66 0.218 5.03 60
2 1/2" 2.875 0.203 5.80 0.276 7.67 75.5
3" 3.500 0.216 7.58 0.300 10.26 88.5
4" 4.500 0.237 10.80 0.337 15.00 114
5" 5.563 0.258 14.63 0.375 20.80 140
6" 6.625 0.280 18.99 0.432 28.60 165

Understanding NPS vs Actual Size

In the US system (ASTM), the NPS (Nominal Pipe Size) is a name, not a direct measurement. For example, an NPS 1 pipe has an outer diameter of 1.315 inches. The naming convention relates to the approximate internal diameter of standard pipes used historically.

Schedule 40 vs Schedule 80

Pipes of the same NPS have the same Outer Diameter. The difference is in the wall thickness:
  • Schedule 40: Standard weight. Used for most plumbing, water, and gas lines.
  • Schedule 80: Extra heavy wall. Used for high-pressure applications or where physical durability is required.
Note: Sch 80 pipes have a smaller internal area, restricting flow slightly compared to Sch 40.

Frequently Asked Questions

What is the most common pipe schedule?

Schedule 40 is the industry standard for residential and commercial plumbing.

How do I calculate pipe weight?

The chart above provides the calculated weight in lbs/ft based on ASTM densities.