Pipe Size Chart & Converter
NPS, DN & actual OD.
NPS, DN & actual OD.
How to use Pipe Size Chart & Converter
- Enter a pipe size as NPS, DN, or actual OD
- Read the equivalent sizes in millimetres and inches
- Note where nominal size stops matching the real diameter
About Pipe Size Chart & Converter
Convert pipe sizes between NPS (nominal pipe size, inches), DN (nominal diameter, metric) and the actual outside diameter in millimetres and inches. Enter any one value and the rest fill in, along with a note on where the nominal number stops matching the real size.
A "2-inch" pipe doesn't measure 2 inches across — that's the trap a generic converter falls into — so this chart is built on the real ASME dimensions. The same outside diameters apply to Schedule 40 and Schedule 80 PVC and plastic pipe, because they share the Iron Pipe Size (IPS) system with steel, so a nominal size gives one OD whether the pipe is metal or plastic; the OD stays fixed across schedules while only the wall thickness changes. NPT thread sizes use the same nominal designations, so the figure you enter is also the thread's pipe size.
It's worth knowing what this doesn't do: picking a natural gas line size is a capacity calculation from BTU load and run length, so a gas sizing chart chooses the diameter and this tool then gives that pipe's actual OD and DN. Copper tube and exhaust tubing use different conventions — copper's nominal size runs smaller than its OD, and exhaust is quoted by true OD — so they aren't part of this IPS table. It's completely free, needs no sign-up, and runs entirely in your browser.
Read it as a pipe size chart — nominal size to outside diameter in inches and millimetres — or convert a single measurement.
Frequently asked questions
- What is DN50 in inches?
- DN50 is NPS 2, and its actual outside diameter is 60.3 mm (2.375 inches). Below NPS 14 the nominal number is a label, not the measured size.
- How do I convert NPS to DN?
- It's a fixed nominal mapping, not a multiplication — NPS 2 is DN 50 (not DN 51), NPS 4 is DN 100, and so on. The tool has the full table.
- What is the actual outside diameter of a 2-inch pipe?
- 60.3 mm, or 2.375 inches. The nominal '2 inch' is a size name; the outside diameter is fixed while the wall thickness changes with the schedule.
- Why isn't the nominal pipe size the real diameter?
- Nominal sizes are historical. For small pipe (below NPS 14) the number roughly relates to the old bore, so the outside diameter is always a bit larger; from NPS 14 up, the nominal number equals the outside diameter in inches.
- Does the outside diameter change with the schedule?
- No — the outside diameter stays the same for a given NPS across all schedules (40, 80, etc.); only the wall thickness and inside diameter change.
- Does this pipe size chart work for PVC?
- Yes. Schedule 40 and Schedule 80 PVC use the same Iron Pipe Size outside diameters as steel, so a 2-inch Sch 40 PVC pipe has the same 60.3 mm OD shown here. Only alternative systems like SDR or CTS tubing follow a different set of dimensions.
- What are the dimensions of Schedule 40 PVC pipe?
- For any nominal size the outside diameter matches steel pipe — 1/2 inch is 21.3 mm (0.840 inch), for example — and the schedule sets the wall thickness. Enter the nominal size to read off the OD; Schedule 80 keeps the same OD as Schedule 40 but with thicker walls.
- How do I use this chart for gas pipe?
- Black iron and steel gas pipe follow the standard NPS dimensions, so this gives the outside diameter and DN equivalent for any nominal size. Just remember that deciding what size line to run is a separate capacity calculation, not a dimension lookup.
- What size natural gas pipe do I need?
- That depends on the appliance's BTU demand and the distance from the meter, which a gas sizing table or your local code chart works out — this tool won't pick the size for you. Once you know the nominal size, enter it here to get the actual OD and metric DN.
- What is the NPT thread size for a 1/2 inch pipe?
- NPT thread sizes use the same nominal pipe designations, so a 1/2-inch NPT fits 1/2-inch nominal pipe, whose outside diameter is 21.3 mm (0.840 inch). The thread number is the pipe size, not the measured diameter of the threads.
- Does this work for copper pipe?
- Not directly. Copper tube uses a different convention where the nominal size is about 1/8 inch smaller than the real outside diameter — 1/2-inch copper is 0.625 inch OD — whereas this chart is built on the Iron Pipe Size system used for steel and PVC.
- Can I use this for exhaust pipe?
- Exhaust tubing is normally quoted by its true outside diameter, so a '2.5 inch' exhaust really is 2.5 inches (63.5 mm) across. Treat those numbers as actual OD rather than nominal pipe size; this converter is for NPS/IPS pipe where the label and the OD differ.