Talk:Nominal Pipe Size

Thank you contributors!
I am really surprised to see this entry. Good work. Excellent effort.

THIS IS VERY HELPFULLYItalicTHANKS FOR YOU SUPPORT text

Very Useful information. I had been looking for this information for months. Now that I have this info, life becomes so much easier.. Very good work, thank you... Kindly arrange the table converter from NPS to DN —Preceding unsigned comment added by 122.161.30.137 (talk) 07:27, 9 November 2007 (UTC)

The article states refers to McGraw Hill Piping Handbook and states in a note that the handbook disagrees with information presented in the article, to whit: Allowable pipe pressure is reduced as pipe diameter increases for a given schedule number. I do not believe that is the case. The formula referred to: Schedule = 1000 x pressure/allowable stress of material, does not imply that allowable pressure is constant for a given schedule over all pipe sizes as the writer of your article seems to conclude. The stress in the pipe is governed by the hoop stress formula which is basically: Stress = pressure x pipe internal radius/wall thickness. Since stress produced in a pipe wall for any given pressure will rise as the pipe radius (i.e. pipe size) increases, it follows that the allowable pressure for a given schedule pipe (i.e. wall thickness & material) will be reduced as the radius increases. Thus both the article and the formula presented in Mcgraw Hill Handbook are correct & consistant. — Preceding unsigned comment added by 96.44.100.81 (talk) 01:06, 19 March 2012 (UTC)

Lamp pipe (nipple) threads: 1/8-IP, 1/4-IP
Lamps and light fixtures here in the U.S. use standard pipe nipples of size "1/8-IP". I googled "1/8-IP" and found that these are nicely explained at, which says that they come from a 19th-century standard for wrought iron pipe by a company called Briggs. Their cited source is "Standard Pipe and Pipe Threads." Transactions of the American Society of Mechanical Engineers, volume 8, Page 29. I suspect that maybe this IP standard evolved into NPS, but I do not know that as fact. It would be great if someone who works in engineering related to pipe could work this info into this article or whichever other article would be logical. I won't have time to read and research into this, but maybe someone who is already well versed in this field can contribute the info to Wikipedia without too much time expenditure. — ¾-10 16:37, 21 November 2007 (UTC)
 * Well, the article already mentions iron pipe size, which seems to be what you're talking about.--Yannick (talk) 01:27, 22 November 2007 (UTC)


 * Ah, OK, upon rereading iron pipe size, I find that it is probably referring to one and the same thing. Thanks. One thing I don't get. According to American Machinists' Handbook, 2nd ed, pp 42-43, the Briggs threads are actually taper threads, for sealed joints; but yet they are used in lamps and light fixtures today as a non-taper thread. (You can buy nipples in any length, from ½" to 12", with all threads perfect, i.e., full and not tapering). I guess there is nothing to "get"—it is what it is—but I am surprised that they effectively took a taper thread standard and morphed it into what is essentially a machine screw thread standard. And the major diameter is .375, rather than .405. Essentially it is a little ⅜-27 machine screw thread, standard to nothing but lamps and light fixtures. I wanted to just buy some cap screws with this thread, but now I see why my light fixture was made stupidly to begin with: you can't buy them. It looks like I may have to make them the ole-fashioned way, with the quick-change gear-box set to 27 and a blank turned to .375. I didn't expect to have to do this simple job from scratch. I am a little miffed that we are still bound to this size in 2007. I vote for abolishing it tomorrow. To hell with maintaining backwards compatibility with any legacy light fixtures; let the antiquarians turn custom threads when they need them—I want mine in a box from McMaster-Carr! Oh well, it is late and I will stop ranting! — ¾-10 03:07, 22 November 2007 (UTC)


 * Hmmm. There's a straight (non-tapered) version of the NPT called NPSM that's used for hoses and mechanical joints. But that .375 diameter doesn't sound right. I agree with abolishing legacy threads; let's just settle on M10 for light fixtures... (I'm well aware that would not be popular in the Western hemisphere.)--Yannick (talk) 04:41, 22 November 2007 (UTC)

What is the thread called on a (U.S.) standard shower riser with OD of 5/8" (.625)
This is the pipe that your shower head screws onto. The OD is 5/8" (.625). What is the name of this thread? I can't figure out this pipe size and pipe thread standard BS. Any help out there? — ¾-10 18:48, 12 January 2008 (UTC)

The typical size for a shower pipe in the US is 1/2" NPT. An exception is the Price Pfeister brand showerhead nipple that has a kind of ball and socket joint near the head, but goes into the wall with 1/2" NPT WonderWheeler (talk) 06:12, 8 May 2009 (UTC)

XH, XXH
I would like to see a brief paragraph added regarding extra heavy and double extra heavy along the same lines as XS and XXS, perhaps following the first paragraphy under History. I think this would be particularly helpful for anyone perusing a pipe table who is trying to make sense of it all. I've seen a number of vendor sites that explain this already. I'll add it to my to-do list, but anyone else who agrees is free to take a shot at it.--CheMechanical (talk) 21:16, 17 August 2008 (UTC)

Amendment: I've been looking at so many Wiki pages, I overlooked the fact that I there is already something on XH and XXH in the History section. (I searched the page using only the abbreviations before I posted, but they are spelled out instead. I think I might remedy this.)  I would like to amend my request to perhaps have someone research the history of these terms rather than just leaving a reference to these being alternate terminology. I think it might be important to point out that the terms were intended to be superseded by a newer system but have managed to hang on just like XS and XXS.--CheMechanical (talk) 22:15, 17 August 2008 (UTC)

STD, XS, and XXS; Electrical; Copper
STD, XS, and XXS: these abbreviations are used by structural engineers as they are listed in their reference books for common steel shapes. At least by my experience in the US. Structural engineers prefer steel columns and the like described by call-outs based on dimensions rather than what the bursting strength of it would be if used as a pressure pipe only.

Electrical: We might also mention that the NPS standards is also used in electrical fittings in the US in PVC and regular steel electrical conduit (not EMT etc). Except, that the threads on fittings and conduit are not tapered (possible exception of full lengths of standard steel conduit). This lack of tapering allows the use of bushings, locknuts et cetera, although they are not water tight. The PVC fittings are typically glued, although male and female threaded adapters are made. This is similar to the 1/8" and 1/4" nipples (previously discussed) that grew out of the use of gas fittings for lights, and even the term keyed and keyless lights and lampholders that grew out of the use of gas luminaires.

Perhaps someone should also edit the article to mention that these nominal pipe sizes are based on the use of steel pipe, and they were extended to brass and PVC pipe, but do not hold true for copper! Copper pipe in the US at least, comes in different thickesses, and the outside diameter is based on the nominal size plus 1/8". That is, 1/2" copper plumbing pipe (not refrigeration tubing) is exactly 5/8" outside diameter.

There is also standard for PVC pipe below schedule 40, for irrigation use called PS125 or something like that. Outside diameter matches NPS.

CPVC and PEX pipe (and the old PB pipe) do not match NPS, but use different standards WonderWheeler (talk) 06:08, 8 May 2009 (UTC)

NPS 3/4" and 1" seem to be missing from the tables
Subject line says it all.

Thanks. —Preceding unsigned comment added by 72.42.86.250 (talk) 14:36, 21 June 2009 (UTC)

In New Zealand there is some usage of "SN ratings". I found one source which indicates an "SN rating" is the same as a "schedule number" - can anybody confirm this?

Hmmm - a local source equates the SN number with the Load to achieve 5% deflection (kn/m/m)...

Ah - our SN numbers are defined by AS/NZS 5065 —Preceding unsigned comment added by 202.89.38.105 (talk) 04:00, 14 October 2009 (UTC)

polyethylene tubing
What are the actual OD, ID, and wall dimensions of common 0.5 to 2-inch black plastic "Poly Pipe" polyethylene tubing in the US? In other countries? -96.237.78.13 (talk) 00:43, 18 August 2010 (UTC)

The standard is here, but is not free: http://www.astm.org/Standards/D2239.htm ASTM D2239 - 03 Standard Specification for Polyethylene (PE) Plastic Pipe (SIDR-PR) Based on Controlled Inside Diameter

SDR stands for "Standard Diameter Ratio" which is the outside diameter divided by the wall thickness. A 2" SDR 7 product would have the outside diameter of 2.375" and a wall thickness of 0.339" (2.375/0.339 = 7).

SIDR stands for Standard Inside Diameter Ratio" which is the inside diameter divided by the wall thickness. The higher the number, the thinner the wall thickness.

Some dimension info for 0.75 to 2.00 pipe is here: http://www.superlon.com/supertuff.pdf

Two-foot sections of sample black plastic pipe at HomeDepot measure approx:
 * 1/2 -- 0.6 -- 0.78
 * 3/4 -- 0.84 -- 1.0

They are labeled:

POTABLE PRESSURE PIPE 1/2 ID 100PSI SIDR 15 PE 3608 ASTM D2239

POTABLE PRESSURE PIPE 3/4 ID 100PSI SIDR 15 PE 3608 ASTM D2239

-96.237.78.13 (talk) 23:38, 25 August 2010 (UTC)

Incorrect Thicknesses on Tables
I notice some of the thicknesses reported in the tables found on this page do not follow sizing trends. I'm pretty sure some of them are incorrect(see NPS 12 sch 40 and below). Does anybody have the actual thicknesses for these pipes? —Preceding unsigned comment added by 67.137.125.106 (talk) 00:15, 29 December 2010 (UTC)

CPVC versus PVC
The article on nominal pipe sizes mentions PVC and CPVC “in the same breath” but does not say that the actual sizes differ even though the sizes stamped on the pipe are the same, ½ inch for example. The CPVC (yellowish tint) is a true ½ I.D. but the white PVC is about 5/8. Supposedly the CPVC was developed because PVC cannot take hot water. CPVC is being used in central Florida because the copper pipe laid in the slab of homes is developing pinhole leaks. I don’t feel qualified to edit the article but would appreciate it if someone could append a comment to it noting that PVC and CPVC pipe designated with same size are incompatible with regard to fittings. Dbvogt (talk) 00:06, 17 August 2011 (UTC)

STD Sizes
in NPS 10 - 24 it is incorrectly labeled as 40s/STD. STD changes depending on the size of the pipe. a 24" pipe STD size is 20 and a 10" pipe STD size is 40s. — Preceding unsigned comment added by 52.129.8.49 (talk) 16:36, 15 May 2012 (UTC)

ASME Standard Number
The "Application" section begins with this sentence "Based on the NPS and schedule of a pipe, the pipe outside diameter (OD) and wall thickness can be obtained from reference tables such as those below, which are based on ASME standards B36.10M and 5.19M." I can not find an ASME Standard numbered "5.19M". Should "5.19M" be "B36.19M" instead? — Preceding unsigned comment added by 12.0.152.114 (talk) 14:29, 31 May 2012 (UTC)


 * Yup, that was vandalism from last January. Fixed.--Yannick (talk) 17:53, 31 May 2012 (UTC)

OD Tolerances
I removed the OD tolerances note (just under the first table) because it references a specific product type (Ni-Fe-Cr-Si Steel Pipe); it's in general incorrect. The correct standard is ASTM A999 if anyone wants to correct the numbers and the reference. Bobxii (talk) 18:53, 3 June 2013 (UTC)

ASME Warning Note
The ASME code books are engineering codes designed and discussed by countless professionals for use in potentially deadly or publicly dangerous applications of construction.

when quoting Specific paragraphs in the ASME code, bear in mind that the code is changed every 2-4 years (typically). the specific section you have referenced may move around. I suggest against quoting ASME-specific quotes in these articles. This page is not maintained by specialists in the field, therefore claims should not be made regarding ASME-specifics. Instead, make a general reference to the ASME code.

Wiki articles are not regulated, and a misinterpretation, vandalism, poorly worded section, or quoting a paragraph that has been removed or changed from the ASME code can result in an engineering disaster. We should not be encouraging code interpretation on Wiki articles. 75.159.163.218 (talk) 20:48, 9 February 2015 (UTC)


 * Readers misusing information is *not* Wikipedia's responsibility. Standard changes isn't a reason to not include information from the standards provided they have become common practice as there often is obscure details only the publishers of the standards actually care about.
 * The one concession I'll make is the importance to specify exactly which version of the standard the quote is from, so the readers relatively easy can verify if the source is outdated or not. 195.196.97.2 (talk) 08:50, 5 March 2024 (UTC)

Schedule 5, 3/8 NPS and smaller
ASME B36.10M-2004 does not define wall thicknesses for Schedule 5 pipe in NPS 1/8, 1/4, and 3/8. Nor does ASME B36.19M-2004 define wall thicknesses for these sizes in Schedule 5S, though it does have entries for them. Yet there seems to be a widespread belief, including in this article, that these wall thicknesses are defined. Where do those numbers come from?

Similarly for 3½ NPS XXS, this combination of size and weight is not defined in the referenced standard.

Cstaffa (talk) 17:43, 10 April 2017 (UTC)

Additional size
There is also a 1/16" size. OD 5/16", 27 tpi. agb 173.233.167.50 (talk) 22:56, 27 January 2023 (UTC)

"Non-dimensional number"
"Non-dimensional number" is an interesting usage; is it an engineering term of art? It could be easily confused with dimensionless number, something completely different. If "non-dimensional number" isn't a term of art, perhaps we could use another formulation like "approximate dimension"? &mdash; The Anome (talk) 08:29, 2 June 2024 (UTC)


 * It's probably a nonce term, not an established jargon. I think it was written that way to try to emphasize that the number in an NPS size is not a size in inches (or any other unit of length) of any of the pipe's dimensions. But there must be a clearer way of saying that, if that's the intention. Indefatigable (talk) 16:23, 3 June 2024 (UTC)