Plumbing pipe is sized by nominal bore — a name like ½" or 25 mm that refers roughly to the inside diameter. Fittings (elbows, tees, valves) are matched to the same nominal size. This chart covers the common sizes we stock in PVC, CPVC and GI.
Inch to mm size chart
| Nominal (inch) | Nominal (mm) | Typical use |
|---|---|---|
| ½" | 15 mm | Taps, branch lines to fixtures |
| ¾" | 20 mm | Main branch & tank-to-line runs |
| 1" | 25 mm | House supply mains, risers |
| 1¼" | 32 mm | Building risers, pump lines |
| 1½" | 40 mm | Risers, larger supply |
| 2" | 50 mm | Mains, pump & tank lines |
| 2½" | 65 mm | Building mains, fire lines |
| 3" | 80 mm | Large mains, fire-fighting |
| 4" | 100 mm | Large supply / drainage |
Drainage (SWR) pipe sizes
Drainage and waste pipe is sized differently — by outside diameter in mm:
| Size | Typical use |
|---|---|
| 75 mm | Waste water (basins, sinks, floor traps) |
| 110 mm | Soil / WC lines |
| 160 mm | Large external drains, mains |
How to choose the right size
- Fixtures (tap, WC, basin): ½" (15 mm) branch lines.
- Home supply main: ¾"–1" (20–25 mm) depending on number of taps and pressure.
- Building riser / pump line: 1¼"–2" (32–50 mm) and up, by load.
- Drainage: 75 mm waste, 110 mm soil, 160 mm external.
Not sure which size your job needs? Tell us the application and we'll guide you. Browse PVC & CPVC pipe, GI pipe or SWR drainage fittings.