UK copper pipe is sold by its outside diameter, which makes matching insulation straightforward — but there are a few common points of confusion worth understanding before you buy.
UK copper pipe sizes and their outside diameters
UK copper pipe follows BS EN 1057 and is sold by outside diameter. The most common sizes are 15mm OD, 22mm OD, 28mm OD, 35mm OD, 42mm OD, 54mm OD, 76.1mm OD, and 108mm OD. The insulation bore size you need matches these outside diameter figures directly.
Why nominal bore causes confusion
Older plumbing references sometimes use nominal bore (NB) sizing, which refers to the approximate internal diameter of the pipe. A ½" nominal bore copper pipe has a 15mm outside diameter. A ¾" NB pipe has a 22mm OD. A 1" NB pipe has a 28mm OD. Always confirm the outside diameter before ordering insulation.
Matching insulation to copper pipe
Browse our size-specific collections: 15mm pipe insulation, 22mm pipe insulation, 28mm pipe insulation. For all sizes, use our pipe insulation by pipe size hub or browse the full pipe insulation range. Our team is available on 0161 775 1190 to help with any sizing queries.
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