How to measure copper pipe size
- Outside diameter, inches
- 0.88
- Tape around the pipe reads, inches
- 2.75
- Wall thickness, inches
- 0.05
Every figure on this page is computed from the inputs you enter, by the method stated below it. RoughInDesk publishes no market averages and quotes no survey: the defaults are a worked example to replace with your own. The pipe dimensions in the pipe-size tool are the published standard sizes, cited on that page.
How to measure copper pipe size: wrap a tape around the pipe or measure straight across the outside with calipers, then convert the outside diameter to the nominal size, because copper tube's nominal size is an eighth of an inch smaller than its outside diameter under ASTM B88. The pipe size tool on this site does the conversion from the outside measurement for copper, PVC and the rest, free and without an account; RoughInDesk Pro keeps the sizes with the estimate and the riser diagram against the job.
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Measure the outside, not the inside
The inside diameter changes with the wall thickness, Type K, L or M, so it cannot tell you the nominal size. The outside diameter is the same for all three types of a given size, which is why the conversion works from the outside. Calipers across the pipe or a tape around it and divided by pi both give the outside diameter.
Convert with the ASTM B88 table
Per ASTM B88, copper measuring 0.625 inches outside is half-inch nominal, 0.875 is three-quarter, 1.125 is one inch, 1.375 is one and a quarter, 1.625 is one and a half and 2.125 is two inch. The pipe size tool on this site does that conversion and the PVC one.
Where it goes wrong
Reading the inside diameter of a cut end and calling it the size; measuring a fitting, which is larger than the tube; measuring over a painted or corroded surface. Measure clean tube, outside, and convert.
Why the size matters on the estimate
The size decides the fittings, the fixture units the line can carry and whether the existing supply can take an added fixture. Pro keeps the sizes with the riser diagram and the estimate against the job. From the vendors' own pricing pages: Tradify lists Lite at $47, Pro at $51 and Plus at $61 per user per month; Jobber lists Core at $49 per month for one user with additional users at $29 each; Housecall Pro lists Basic at $59 per month billed annually or $79 monthly. RoughInDesk Pro is $47 per month for the whole crew.
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How to measure copper pipe size: common questions
Is the pipe size tool free? Yes. It converts the outside diameter to the nominal size for copper, PVC and the rest with no account and no card.
Why is copper's nominal size smaller than its outside diameter? By convention under ASTM B88 the nominal size is an eighth of an inch less than the outside diameter, for every size and every wall type.
Can I measure with a string? Yes: wrap it, measure the length, divide by pi for the outside diameter, then convert.
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