UK Pipe Sizes — Copper, Plastic and Steel Reference

The most common copper pipe sizes in UK domestic plumbing are: 8 mm (micro-bore heating), 10 mm (micro-bore heating), 15 mm (hot and cold water, radiator tails), 22 mm (hot and cold mains, heating flow/return), 28 mm (main heating flow/return, large systems), 35 mm (commercial, large domestic), 42 mm (commercial), and 54 mm (commercial mains). 15 mm and 22 mm account for the vast majority of domestic plumbing work.

Pushfit pipe (e.g., JG Speedfit, Hep2O) uses rubber O-ring seals and can be connected without tools, glue, or heat. It comes in 10, 15, 22, and 28 mm sizes matching copper. Solvent weld pipe (PVC-U) uses a chemical cement to permanently bond joints. It is available in 19.05 mm (3/4"), 21.5 mm (3/4" waste), 32 mm (1.25" waste), 40 mm (1.5" waste), and 50 mm (2" waste) sizes. Pushfit is preferred for speed; solvent weld for permanence.

The standard service pipe from the water main to a UK domestic property is 25 mm blue MDPE (medium-density polyethylene). Inside the property, the mains cold feed is typically 15 mm or 22 mm copper or plastic. For properties with a combi boiler, a 22 mm cold main ensures adequate flow rate. The supply pipe from the boundary stopcock to the property must be at least 25 mm.

Standard UK waste pipe sizes are: 21.5 mm (overflow pipes), 32 mm (basin waste), 40 mm (bath, shower, kitchen sink waste), 50 mm (commercial sinks, urinals), and 110 mm (soil pipe, WC connection). These are outside diameter measurements. Waste pipes should be installed with the correct fall gradient: 18-90 mm/m for 32 mm, 18-45 mm/m for 40 mm pipes.

Yes, barrier-type plastic pipe (PEX, PB, or MLCP with an oxygen barrier layer) is approved for central heating systems in the UK. Popular brands include JG Speedfit Barrier Pipe and Hep2O. The oxygen barrier prevents dissolved oxygen entering the system and corroding radiators and boiler heat exchangers. Standard non-barrier plastic pipe must NOT be used for heating as it is permeable to oxygen.