How to size an air purifier for a UK flat
8 June 2026 · 7 min read
CADR, square metres and open-plan quirks — a practical sizing guide for UK flats and terraced houses in 2026.
Start with the room you care about most
One purifier cleans one air volume well. In a one-bed flat that might be the bedroom; in a family terraced house it is often the lounge. Measure length × width for a rough m² figure, then match the manufacturer’s stated coverage — ideally with a little headroom so the unit is not always on maximum.
CADR (clean air delivery rate) tells you how quickly clean air is delivered. Higher CADR suits bigger or dirtier rooms. Specs vary by pollutant type (smoke, dust, pollen), so compare like with like when you read Amazon listings.
Open-plan and awkward UK layouts
Knock-through lounge-diners behave like larger rooms. A unit rated for 20 m² will struggle in a 35 m² open space. Step up to higher-CADR options such as the Philips Series 3000i or Xiaomi Smart Air Purifier 4, or run two smaller units at opposite ends if noise and budget allow.
Hallways and landings are poor homes for a purifier: air moves past too quickly and doors break the circuit. Park it inside the target room with clear space on all sides.
Ceiling height and furniture
Most UK flats have standard ceiling heights, so floor-area ratings are usually fine. Very tall Victorian rooms hold more air — treat them as larger than the floor m² suggests. Crowded bookshelves and deep sofas also reduce effective circulation; leave a clear path to the intake.
When you are unsure between two sizes, choose the slightly larger CADR and run it on a lower, quieter speed. That is almost always more pleasant than a small unit screaming on turbo.
Compare more models on our feature table or take the quiz.