NPS Pipe Size Chart

Nominal pipe size (NPS) is a North American standard for pipe used in plumbing, process piping, fire protection and structural work — and the “size” is not the actual diameter. This printable pack gives you a complete NPS chart with outside diameters, metric DN equivalents, wall thickness and inside diameter for common schedules, steel weight per foot and an Excel calculator for flow area and weight.

NPS pipe size chart (steel pipe)

Dimensions follow the ASME B36.10M/B36.19M standard for wrought steel and stainless steel pipe. Always confirm with the manufacturer’s data for critical applications.

Why NPS is not the real diameter

For sizes up to 12 inches, the NPS number is a historical name that roughly matched the inside diameter of early iron pipe. The outside diameter was fixed so that fittings and threads always match, and thicker walls were added inward. So a 2-inch pipe has an outside diameter of 2.375 inches whatever its schedule, while its inside diameter shrinks as the wall gets thicker. From NPS 14 upward, the NPS number equals the outside diameter.

What pipe schedule means

The schedule number describes wall thickness relative to size. Schedule 40 is the common “standard” weight for many sizes; Schedule 80 (“extra strong” in many sizes) has thicker walls for higher pressure; Schedule 10 is thin-walled, often used for stainless steel and low-pressure systems such as fire sprinklers. Stainless schedules carry an “S” (10S, 40S, 80S) and match the carbon steel dimensions for most sizes up to 10 inches. For the same NPS, a higher schedule means a thicker wall, smaller inside diameter and higher pressure rating.

NPS vs DN

DN (diamètre nominal) is the metric designation used internationally: NPS ½ is DN 15, NPS 1 is DN 25, NPS 2 is DN 50 and NPS 4 is DN 100. DN numbers are also nominal — the outside diameter of DN 50 steel pipe to ASME dimensions is 60.3 mm. European (EN) and other standards may use slightly different outside diameters for some sizes, so check which standard applies before mixing pipe and fittings from different systems.

Steel pipe weight

The weight of plain-end steel pipe in pounds per foot can be calculated as 10.69 × (OD − wall) × wall, with dimensions in inches. For example, 2-inch Schedule 40: 10.69 × (2.375 − 0.154) × 0.154 ≈ 3.66 lb/ft. The Excel calculator in the pack does this for every row, along with the inside flow area in square inches (π × ID² ÷ 4).

Copper tube, PVC and other materials

PVC Schedule 40 and 80 pipe use the same outside diameters as steel NPS, so the chart applies to their OD and schedules too, though pressure ratings are much lower and temperature-dependent. Copper tube uses a different system (nominal size with types K, L, M) where the outside diameter is ⅛ inch larger than the nominal size. PEX and CPVC tubing sold as “copper tube size” follow copper dimensions. Never assume two systems are interchangeable without checking OD.

What is in the pack

• Printable NPS chart with DN, OD, Schedule 10/40/80 wall and ID (PDF).
• Steel pipe weight per foot table.
• Excel pipe calculator: pick NPS and schedule, get ID, flow area and weight per foot and per length.
• Pipe thread and fitting quick reference (NPT basics).
• Pipe takeoff sheet for estimating lengths and fittings on a job.

Formats

Print-ready PDF charts (US Letter; A4 with “Fit to page”), Excel calculator and takeoff sheet, and Word reference.