Metric or Imperial PVC — How Do I Tell?
UK Flow Centre buying guide
Metric or imperial PVC: identify first, then buy
Metric and imperial PVC are separate systems. This is a measurement-and-compatibility question, not a question of which system is better.
1. Measure the existing pipe
Measure the outside diameter of clean, exposed pipe with a tape or calipers. Do not rely on what it looks like, a rough conversion or the size printed on an unrelated fitting.
Important: metric and imperial PVC fittings are not direct substitutes. Do not force one system into the other or use extra solvent cement to make it fit.
2. Check the joining method
- Solvent-weld fittings: use compatible pipe, fittings, cleaner and cement for that system.
- Threaded connections: identify the thread type and the sealing method required before choosing an adaptor.
- Unions: help future maintenance but still need the correct pipe size and sealing faces.
3. Choose by the job
- New metric pressure pipework: build a complete metric system rather than mixing parts.
- Existing imperial pool or specialist pipework: retain the imperial system unless there is a deliberately designed conversion.
- Repairing a break: identify the original system first; the nearest-looking fitting is often wrong.
Before you order
Take a photograph of the pipe alongside a tape measure, show the fitting from both ends, and say whether it is pressure water, a pool line, drainage or another application. This is more reliable than choosing from a nominal size alone.
Technical guidance from UK Flow Centre, operated by JK Irrigation Ltd.