Copper pipe sizes

By Tom Drake | 26th June 2024 | 3 min read

If you're altering or adding new copper pipework in your home, you need to know which size you need. In this guide, we take you through the most common copper pipe sizes, and where you might use them in your plumbing system.

Jump to:

• 15 mm
• 8 mm & 10 mm
• 22 mm & 28 mm
• Pipe reducers
• Imperial to metric

15 mm Copper pipe

15 mm is the most common copper pipe size in the UK. 15 mm pipe is widely used for transporting water around homes for fixtures such as taps and showers.

15 mm pipes are also used in central heating systems to carry water to radiators.

8 mm & 10 mm Copper pipe

8 mm and 10 mm copper pipes are also known as microbore pipes. These smaller pipes carry water at a lower flow rate than larger sizes and can often be found in older heating systems. You may also find 8mm or 10mm pipes feeding monobloc taps.

22 mm & 28 mm Copper pipe

22 mm and 28 mm copper pipes are mainly used in central heating systems to supply water to boilers, storage cisterns or tanks.

22 mm pipe may sometimes be used to supply water to baths.

Pipe reducers

If you want to change the size of the pipework in your home, you’ll need to use a pipe reducer. These feature inlets of different sizes, so you can connect two pipe sizes to one fitting.

Pipe reducers are available in straight, tee and elbow shapes, giving you the option to change the direction of the pipework as you change the size.

Imperial to metric copper pipework

In the UK, copper pipework measurements were switched from imperial to metric in the early 1970s. This may cause you issues if you want to connect new pipework to an older imperial system. Here, we outline some of the common imperial measurements and their metric equivalents.

½ Inch copper pipes

If your home has ½ inch imperial pipework, you can join it to modern metric 15mm pipes using standard metric compression fittings. ½ inch to 15mm adaptors are available for push fit and soldered joints.

¾ Inch copper pipes

If you have ¾ inch copper pipes, you’ll need to purchase an adaptor to connect them to 22mm pipes.