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Like many items which have "trade sizes" it seems a little ambiguous what the length of a pipe nipple actually means.

For instance, if I see a 4" pipe nipple advertised, what portion of the object is the 4" a measurement of? Is it even a measurement at all? (like 2x4 is not really 2" by 4"...)

Looking at various shopping websites doesn't actually make this very clear. And unfortunately I don't have any examples on hand to examine. Even if I did, I'm not sure if this is an industry "standard" or not.

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I looked at some manufacturer's documentation. Short answer: the stated size is the total length of the pipe nipple including the threaded sections.

This does appear to be consistent among manufacturers (at least in the US / North American market).

Also an important detail is that the length of the threaded sections is standard for each pipe diameter. So with a little information you can figure out what length the unthreaded middle portion of the pipe nipple has.

Length diagram from Anvil Intl.:

enter image description here

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And their accompanying diagram of the available standard nipple lengths. What's important about this is the "close" lengths - these are nipples that are fully threaded, and so its the shortest total length they could be at that diameter. If you subtract this from any of the others you get the unthreaded length.

Example: a 1" size pipe 6" long. The close length is 1 1/2", so the remaining unthreaded portion must be 3 1/2". (Plus or minus 1/8" as noted on the first diagram).

enter image description here

These documents state "APPLICABLE SPECIFICATION: ASTM A733" which means, I think, that these measurements should be consistent among manufacturers.

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The length of the nipple is the length of the pipe it is created from, the overall length from one end to the other. A nipple can threaded on both ends, plain on both ends or plain one end and threaded the other. To calculate the portion of pipe left from end of fitting to end of fitting when it is installed you have to subtract the engagement length of both ends. The "close" length is the shortest nipple length that can be created, when its installed the fittings are right up against each other with no pipe showing. Therefore the close length is 2X the engagement. For other nipples subtract the close length from the overall length to figure out how much pipe length will be left between the fittings. A 1" dia. nipple 6" long would be 4.5" between the fittings not 3.5" as indicated above.

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  • It's called take up and I get it wrong every time which is why I don't pipe fit without a nipple kit. Guessing, grabbing a random length, and holding it in the exact space I expect it to occupy is how I 'measure'.
    – Mazura
    Jun 18, 2021 at 3:15
  • While you're not wrong, this doesn't really seem to add anything to the other answer that's been here for nearly 18 months.
    – FreeMan
    Jun 18, 2021 at 12:55

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