What size air conditioner do I need?

Enter your room dimensions and we’ll tell you the exact BTU rating you need — then show you matching units that are actually in stock right now.

Rough guide: UK rooms need ~340 BTU per square metre. Our calculator adjusts for ceiling height and insulation for a more accurate number.

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Enter your room dimensions →

We’ll calculate your BTU, then show you matching air conditioners that are in stock right now.

What does BTU mean?: BTU (British Thermal Unit) measures how much heat an air conditioner can remove from a room per hour. Higher BTU = cools bigger rooms. For UK homes, aim for about 340 BTU per square metre of floor space.
What happens if I buy too small an AC?: An undersized unit will run constantly without ever cooling the room properly. It'll also use more electricity and wear out faster because it never reaches its target temperature.
Is bigger always better?: No. An oversized unit will cool the room too quickly and shut off before it's dehumidified properly — leaving you with a cold, clammy room. Always match BTU to room size.
Does ceiling height matter?: Yes — taller rooms have more air volume to cool. A room with 3m ceilings needs ~25% more BTU than the same floor area with standard 2.4m ceilings.
How much does it cost to run a portable AC?: A 9,000 BTU unit costs about 25-35p per hour at current UK electricity rates (July 2026). Running it 8 hours a day for a month ≈ £60-85.