Pipe & Fitting Size Finder
Measure a pipe's outside diameter and get its nominal size (1/2 in, DN15, 15A…)
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Measure a pipe's outside diameter on the screen, or enter its circumference, and get the nominal size such as 1/2 in, DN15 or 15A. Use it to identify a water pipe, a fitting or a pipe thread before you buy parts.
How to use
- On your first visit, press "Calibrate screen" and match the screen to a card or a coin.
- Under "Pipe type", choose the table for steel, PVC, copper, PEX or taper pipe thread.
- Under "How to measure", choose "Match a circle", put the pipe end on the guide lines and match the yellow circle to its outer edge. For thick or installed pipes, use "Enter circumference" with a tape measure.
- The nearest size and other candidates appear under "Nominal size". If you know the size, use "Draw a circle for a nominal size" to see it at real size.
How it works
- A circumference is converted with outside diameter = circumference ÷ π.
- A screen reading is off by about 0.5 mm, so all sizes closer together than that are shown as candidates.
- The tables follow KS D 3507 / JIS G 3452, ASME B36.10, ASTM B88, ASTM F876, ISO 7-1, ASME B1.20.1 and others, each value checked in October 2026 against at least two sources. Korean KS PVC pipe (VP, VG) is not included.
Questions and answers
- What is the outside diameter of a 1/2 inch pipe?
- ASME NPS 1/2 steel pipe is 21.3 mm (0.840 in) outside, and the KS/JIS 15A equivalent is 21.7 mm. The nominal size comes from the approximate bore, not the outside diameter.
- Can BSPT (R) and NPT threads be used together?
- No. Their diameters are almost the same, but the thread angle (R 55°, NPT 60°) and the thread count differ, so a mixed joint leaks. Check the marking (R, Rc, PT, NPT) on the part.
- What is the outside diameter of 1/2 inch copper tube?
- ASTM B88 copper tube is always 1/8 in larger than its nominal size, so 1/2 in tube is 5/8 in (15.875 mm) outside.