Steel pipe dimensions · NPS 1/8–24

Pipe Size Chart

Find NPS, DN, outside diameter, and Schedule 40/80 wall thickness and calculated inside diameter in inches or millimeters.

Basis: ASME B36.10-2022 basis
Range: NPS 1/8–24
Schedules: 40 and 80
Use: Dimensions, not pressure

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Fast lookup

Steel Pipe Size Chart — Schedule 40 & 80

One row per NPS so the dimensions most users need are visible side-by-side.

A “2-inch” steel pipe is not 2 inches OD. NPS 2 has a standardized outside diameter of 2.375 in (60.33 mm). NPS and DN are nominal designations.

Common wrought-steel NPS sizes from 1/8 through 24 with Schedule 40 and Schedule 80 nominal wall dimensions. Inside diameter is calculated from nominal outside diameter minus twice nominal wall thickness.
		(in)	Schedule 40		Schedule 80		Action
		(in)	Wall (in)	ID (in)	Wall (in)	ID (in)	Action
NPS 1/8	DN 6	0.405 in	0.068 in	0.269 in	0.095 in	0.215 in
NPS 1/4	DN 8	0.540 in	0.088 in	0.364 in	0.119 in	0.302 in
NPS 3/8	DN 10	0.675 in	0.091 in	0.493 in	0.126 in	0.423 in
NPS 1/2	DN 15	0.840 in	0.109 in	0.622 in	0.147 in	0.546 in
NPS 3/4	DN 20	1.050 in	0.113 in	0.824 in	0.154 in	0.742 in
NPS 1	DN 25	1.315 in	0.133 in	1.049 in	0.179 in	0.957 in
NPS 1-1/4	DN 32	1.660 in	0.140 in	1.380 in	0.191 in	1.278 in
NPS 1-1/2	DN 40	1.900 in	0.145 in	1.610 in	0.200 in	1.500 in
NPS 2	DN 50	2.375 in	0.154 in	2.067 in	0.218 in	1.939 in
NPS 2-1/2	DN 65	2.875 in	0.203 in	2.469 in	0.276 in	2.323 in
NPS 3	DN 80	3.500 in	0.216 in	3.068 in	0.300 in	2.900 in
NPS 3-1/2	DN 90	4.000 in	0.226 in	3.548 in	0.318 in	3.364 in
NPS 4	DN 100	4.500 in	0.237 in	4.026 in	0.337 in	3.826 in
NPS 5	DN 125	5.563 in	0.258 in	5.047 in	0.375 in	4.813 in
NPS 6	DN 150	6.625 in	0.280 in	6.065 in	0.432 in	5.761 in
NPS 8	DN 200	8.625 in	0.322 in	7.981 in	0.500 in	7.625 in
NPS 10	DN 250	10.750 in	0.365 in	10.020 in	0.594 in	9.562 in
NPS 12	DN 300	12.750 in	0.406 in	11.938 in	0.688 in	11.374 in
NPS 14	DN 350	14.000 in	0.438 in	13.124 in	0.750 in	12.500 in
NPS 16	DN 400	16.000 in	0.500 in	15.000 in	0.844 in	14.312 in
NPS 18	DN 450	18.000 in	0.562 in	16.876 in	0.938 in	16.124 in
NPS 20	DN 500	20.000 in	0.594 in	18.812 in	1.031 in	17.938 in
NPS 24	DN 600	24.000 in	0.688 in	22.624 in	1.219 in	21.562 in

Scope: common wrought-steel NPS dimensions only. This chart intentionally keeps the generic “pipe size chart” task focused on NPS/DN/OD and common Schedule 40/80 geometry. For additional wall schedules, use the dedicated Pipe Schedule Chart.

Selected-size detail

Compare Schedule 40 vs. 80 at One Pipe Size

The OD stays fixed for a given NPS. A thicker Schedule 80 wall reduces inside diameter and bore area.

NPS 2 · DN 50Schedule 40 and Schedule 80 shown together

Proportional comparison only; not a printable full-size template.

Selected pipe NPS 2 · DN 50

Outside diameter: 2.375 in

Schedule 402.067 in ID

Wall: 0.154 in
Calculated area: 3.356 in²

Schedule 801.939 in ID

Wall: 0.218 in
Calculated area: 2.953 in²

Same-size schedule effectSchedule 80 has 12.0% less bore area

Field measurement lookup

Identify Pipe Size from OD or Circumference

Measure the outside of the pipe, not the bore. Add wall thickness or ID only if you want to compare which listed schedule is closer.

Fastest method: measure outside diameter with calipers. If you only have a tape, measure circumference and the tool converts it to OD using OD = circumference ÷ π.

Enter a measurement above.The closest standardized OD will appear here.

How to Read a Pipe Size Chart

NPS and DN are nominal size designations. For a given NPS, outside diameter stays fixed while schedule changes wall thickness and therefore calculated inside diameter.

NPS: Nominal Pipe Size, a standardized pipe and fitting designation—not a measured diameter.

DN: Diameter Nominal, the associated metric designation—not an exact millimeter diameter.

OD: Outside diameter. Use OD for fit-up, supports, clamps, clearances, and field identification.

ID: Calculated inside diameter: OD − 2 × nominal wall thickness.

Most common comparison

Schedule 40 vs. Schedule 80 Pipe Dimensions

At the same NPS, Schedule 40 and Schedule 80 use the same standardized OD. Schedule 80 has a thicker wall, so its calculated ID and bore area are smaller.

NPS 2 Schedule 402.375 in OD

0.154 in wall · 2.067 in calculated ID

NPS 2 Schedule 802.375 in OD

0.218 in wall · 1.939 in calculated ID

Need additional schedules? Use the Pipe Schedule Chart instead of assuming Schedule 40/80 dimensions apply to other schedules.

Designation trap

Schedule 40 vs. STD and Schedule 80 vs. XS

STD (standard weight) and XS/XH (extra strong) are legacy wall designations that coincide with some schedule dimensions only over part of the NPS range. They are not universal synonyms.

Schedule 40 and STD diverge

At NPS 12, Schedule 40 wall is 0.406 in, while STD wall is 0.375 in.

Schedule 80 and XS diverge

At NPS 12, Schedule 80 wall is 0.688 in, while XS/XH wall is 0.500 in.

How Pipe ID and Bore Area Are Calculated

Choose the NPS or associated DN designation.
Read standardized outside diameter and nominal wall thickness.
Calculate ID = OD − 2t.
Calculate circular bore area with A = πID² ÷ 4.
Verify tolerances, material, service, and code requirements before design use.

Why nominal size does not equal measured diameter

NPS is a standardized designation used to match pipe, fittings, valves, and components. It should not be interpreted as the actual OD or ID. This becomes obvious with common sizes such as NPS 2, whose standardized OD is 2.375 inches.

Worked dimensional examples

Pipe Size Chart Examples

NPS 2 Schedule 40 ID

Given: OD = 2.375 in and t = 0.154 in.

Method: ID = 2.375 − 2(0.154) = 2.067 in.

Result: Nominal internal area is about 3.356 in².

NPS 2 Schedule 40 vs. 80

Both use 2.375 in OD, but wall increases from 0.154 to 0.218 in. ID falls from 2.067 to 1.939 in, reducing nominal bore area by about 12.0%.

Avoid the common sizing errors

Pipe Size Chart Mistakes to Avoid

Use this chart for

Steel NPS and DN lookup
Outside-diameter identification
Schedule 40/80 geometry

Verify separately

Material grade and temperature
Pressure design and corrosion allowance
Wall tolerance and product availability

Do not mix with

PVC or CPVC schedules
Copper Types K, L, M, or DWV
HDPE SDR or tubing OD systems

Important Pipe Size Chart Limitations

Schedule is not a pressure rating

Schedule identifies a dimensional wall series. Allowable pressure depends on material specification, temperature, manufacturing tolerance, corrosion allowance, joining method, governing code, and project conditions.

Calculated ID and bore area exclude wall-thickness tolerance, lining, deposits, corrosion, coatings, and out-of-roundness. Use approved manufacturer data and the governing project specification when minimum bore or fit is critical.

Pipe Size Chart Sources, Scope, and Data Rights

Common wrought-steel NPS dimensions · Schedules 40 and 80 · limited educational dimensional subset

This page publishes a limited educational dimensional subset focused on common NPS sizes with Schedule 40 and 80 values plus original derived calculations. It does not reproduce the complete ASME B36.10 table or provide a bulk standards-derived download.

ASME B36.10-2022 — Welded and Seamless Wrought Steel PipePrimary standard basis for wrought-steel pipe dimensions.
ISO 6708:1995 — Pipework Components, Definition and Selection of DNDefinition basis for DN as a nominal size designation.
American Piping Products — Pipe Dimension ChartIndependent published cross-check for common OD and wall values.

Primary standard basis: ASME B36.10-2022
Displayed scope: NPS 1/8–24; Schedules 40 and 80
Source-controlled fields: NPS, DN, nominal OD, nominal wall
Calculated fields: Nominal ID and circular bore area
Known exclusions: Other schedules, S schedules, tolerances, pressure ratings, grades, non-steel systems
Publisher: Turn2Engineering

Pipe Size Chart FAQs

Is nominal pipe size the same as inside diameter?

No. NPS is a nominal designation. Actual calculated ID changes with wall thickness, so Schedule 80 has a smaller ID than Schedule 40 at the same NPS.

Does pipe schedule change outside diameter?

What is the outside diameter of 2-inch pipe?

Are DN and NPS exact unit conversions?

How do I identify pipe size from circumference?

Does Schedule 80 pipe have one pressure rating?

Is Schedule 40 always the same as STD pipe?

Pipe Size Chart Summary

Use the table first: find NPS, DN, or measured OD, then compare Schedule 40 and Schedule 80 wall thickness and calculated ID side-by-side. Use the selected-size visualization or field-measurement finder only when you need more detail.

For final design, verify the complete current standard, material specification, manufacturing tolerance, governing piping code, project conditions, and approved product data.

Steel Pipe Size Chart — Schedule 40 & 80

Compare Schedule 40 vs. 80 at One Pipe Size

Identify Pipe Size from OD or Circumference

How to Read a Pipe Size Chart

Schedule 40 vs. Schedule 80 Pipe Dimensions

Schedule 40 vs. STD and Schedule 80 vs. XS

Schedule 40 and STD diverge

Schedule 80 and XS diverge

How Pipe ID and Bore Area Are Calculated

Why nominal size does not equal measured diameter

Pipe Size Chart Examples

NPS 2 Schedule 40 ID

NPS 2 Schedule 40 vs. 80

Pipe Size Chart Mistakes to Avoid

Use this chart for

Verify separately

Do not mix with

Important Pipe Size Chart Limitations

Pipe Size Chart Sources, Scope, and Data Rights

Related Pipe References and Calculators

Pipe Size Chart FAQs

Pipe Size Chart Summary