What is the outside diameter of 6 inch pipe?

6.625 in, for every schedule. Only the wall thickness and bore change between schedules.

What is the difference between Schedule 40 and Schedule 80?

Wall thickness, and therefore bore and weight. On 6 in pipe, Schedule 40 has a 0.280 in wall and a 6.065 in bore, while Schedule 80 has a 0.432 in wall and a 5.761 in bore. Outside diameter is 6.625 in for both.

Is 2 inch pipe actually 2 inches?

No. A 2 in nominal pipe has a 2.375 in outside diameter. Nominal size is a label with no fixed relationship to any measured dimension — it is closest to the Schedule 40 bore in the smaller sizes, which is where the convention originated.

What is the inside diameter of 1 inch Schedule 40 pipe?

1.049 in. The outside diameter is 1.315 in and the Schedule 40 wall is 0.133 in, so the bore is 1.315 − 2 × 0.133 = 1.049 in.

How much does 6 inch Schedule 40 pipe weigh?

About 18.97 lb/ft. Weight is the cross-sectional area of the steel annulus multiplied by the density of steel, so it rises with wall thickness at a fixed outside diameter.

Nominal Pipe Size — the dimensionless label used to specify pipe in North American practice. DN (diamètre nominal) is the metric equivalent and is a close but not exact conversion: NPS 6 is DN 150.

Pipe Schedule Chart — NPS, OD, Wall Thickness and Weight

Sources and scope for this page: ASME B36.10M-2018, covering outside diameters and Schedule 40 / 80 wall thicknesses. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. Full sources, values and limits on this page.

Page last changed 2026-10-19 · based on ASME B36.10M-2018

Quick Answer

Pipe is specified by nominal size and schedule, and the schedule sets the wall thickness. For a given nominal size the outside diameter is fixed — only the bore changes. A 6 in Schedule 80 pipe has a thicker wall and therefore a smaller bore than Schedule 40, but both have a 6.625 in outside diameter.

Find a pipe size

Steel Pipe Dimensions — Schedule 40 and 80

Nominal size in^[1]	Outside dia in^[1]	ID, Sch 40 in^[2]	ID, Sch 80 in^[2]	Wall, Sch 40 in^[1]	Wall, Sch 80 in^[1]	Weight, Sch 40 lb/ft^[3]	Weight, Sch 80 lb/ft^[3]
1/2 #	0.840	0.622	0.546	0.109	0.147	0.85	1.09
3/4 #	1.050	0.824	0.742	0.113	0.154	1.13	1.48
1 #	1.315	1.049	0.957	0.133	0.179	1.68	2.17
1 1/4 #	1.660	1.380	1.278	0.140	0.191	2.28	3.00
1 1/2 #	1.900	1.610	1.500	0.145	0.200	2.72	3.64
2 #	2.375	2.067	1.939	0.154	0.218	3.66	5.03
2 1/2 #	2.875	2.469	2.323	0.203	0.276	5.80	7.67
3 #	3.500	3.068	2.900	0.216	0.300	7.58	10.26
4 #	4.500	4.026	3.826	0.237	0.337	10.80	15.00
5 #	5.563	5.047	4.813	0.258	0.375	14.63	20.80
6 #	6.625	6.065	5.761	0.280	0.432	18.99	28.60
8 #	8.625	7.981	7.625	0.322	0.500	28.58	43.43
10 #	10.750	10.020	9.562	0.365	0.594	40.53	64.50
12 #	12.750	11.938	11.374	0.406	0.688	53.58	88.72
14 #	14.000	13.124	12.500	0.438	0.750	63.51	106.25
16 #	16.000	15.000	14.312	0.500	0.844	82.86	136.76
18 #	18.000	16.876	16.124	0.562	0.938	104.78	171.11
20 #	20.000	18.812	17.938	0.594	1.031	123.24	209.09
24 #	24.000	22.624	21.562	0.688	1.219	171.48	296.90

Outside diameter is fixed per nominal size regardless of schedule — the schedule changes only the wall thickness and therefore the bore. Nominal size is a label, not a dimension: 6 in pipe has a 6.625 in outside diameter. Weight is computed for steel at 0.2836 lb/in³.

Why Outside Diameter Is Fixed

Pipe is joined by threading or welding to fittings that must interchange. If outside diameter varied with wall thickness, every fitting would need to match a specific schedule. So the standard fixes the outside diameter per nominal size and lets the bore vary instead.

The consequence is that a thicker schedule does not give you a bigger pipe — it gives you a smaller hole in the same outside envelope. Schedule 80 on 6 in pipe reduces the bore from 6.065 in to 5.761 in.

Nominal size has no fixed relationship to any actual dimension. It is closest to the old inside diameter for Schedule 40 in the smaller sizes, which is where the naming came from, but it matches neither the bore nor the outside diameter today.

Reading the Schedule Number

For sizes up to 12 in, the schedule number is roughly 1000 × P / S, where P is the working pressure and S the allowable stress — so a higher schedule means a higher pressure rating. Above 12 in the relationship breaks down and the schedules are simply defined values.

Common schedules are 10, 20, 40, 60, 80, 100, 120, 140 and 160, plus the old designations STD, XS and XXS. Schedule 40 and STD are identical up to 10 in; Schedule 80 and XS are identical up to 8 in. Beyond those sizes they diverge, which is a common source of confusion when reading older drawings.

Frequently Asked Questions

What is the outside diameter of 6 inch pipe?: 6.625 in, for every schedule. Only the wall thickness and bore change between schedules.
What is the difference between Schedule 40 and Schedule 80?: Wall thickness, and therefore bore and weight. On 6 in pipe, Schedule 40 has a 0.280 in wall and a 6.065 in bore, while Schedule 80 has a 0.432 in wall and a 5.761 in bore. Outside diameter is 6.625 in for both.
Is 2 inch pipe actually 2 inches?: No. A 2 in nominal pipe has a 2.375 in outside diameter. Nominal size is a label with no fixed relationship to any measured dimension — it is closest to the Schedule 40 bore in the smaller sizes, which is where the convention originated.
What is the inside diameter of 1 inch Schedule 40 pipe?: 1.049 in. The outside diameter is 1.315 in and the Schedule 40 wall is 0.133 in, so the bore is 1.315 − 2 × 0.133 = 1.049 in.
How much does 6 inch Schedule 40 pipe weigh?: About 18.97 lb/ft. Weight is the cross-sectional area of the steel annulus multiplied by the density of steel, so it rises with wall thickness at a fixed outside diameter.
What does NPS mean?: Nominal Pipe Size — the dimensionless label used to specify pipe in North American practice. DN (diamètre nominal) is the metric equivalent and is a close but not exact conversion: NPS 6 is DN 150.

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

#	Source	Type	Revision / method
[1]	ASME B36.10M — Welded and Seamless Wrought Steel Pipe	reference	ASME B36.10M-2018 — source
[2]	Inside diameter	derived	ID = OD − 2 × wall thickness.
[3]	Weight per foot	derived	Weight = (π/4)(OD² − ID²) × 0.2836 lb/in³ × 12 in/ft, for steel.

Data Sources

Standard	Revision	What it covers on this page
ASME B36.10M — Welded and Seamless Wrought Steel Pipe	ASME B36.10M-2018	outside diameters and Schedule 40 / 80 wall thicknesses

Verification scope

No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

Derived values — the following values on this page are calculated, not taken directly from the standard:

Value	How it is derived
Inside diameters and weights	Computed from outside diameter and wall thickness — see the formulas above.

Schedule 40 and 80 only. Schedules 10, 160, XXS and the intermediate schedules have different wall thicknesses and are published in the same standard. Stainless pipe uses the same outside diameters but a different wall-thickness series (B36.19M).

Accuracy and use. Use the source notes and recorded verification scope above to assess each value. Calculated values follow the stated derivations; compilation values may lack a confirmed original document or product condition. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Read the source notes, calculation methods and verification scope above before reusing a value. To cite this page:

Plain text

Engineering Reference. "Pipe Schedule Chart." https://refmanual.com/charts/pipe-schedule/ (accessed 2026-11-09). Data from ASME B36.10M — Welded and Seamless Wrought Steel Pipe, ASME B36.10M-2018.

BibTeX

@misc{pipe-schedule,
  title        = {Pipe Schedule Chart},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/pipe-schedule/}},
  note         = {Accessed: 2026-11-09},
  source       = {ASME B36.10M — Welded and Seamless Wrought Steel Pipe, ASME B36.10M-2018}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Pipe Schedule Chart
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/pipe-schedule/
PY  - 2026
DA  - 2026-11-09
N1  - Source: ASME B36.10M — Welded and Seamless Wrought Steel Pipe, ASME B36.10M-2018
ER  -

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.