What size air conditioner do I need?
Portable air conditioners are rated in BTU. Buy too small and the unit runs flat-out and never cools the room on the hottest days. Enter your room below for a sensible buying range.
Your room
Recommended size
5,400BTU
≈ 1.6 kW cooling
Sensible buying band
4,900 – 6,300 BTU
A rule-of-thumb estimate. Undersized units run flat-out and struggle on the hottest days — aim for the top of the band if in doubt.
How the estimate works
We start from roughly 340 BTU per square metre for a standard-ceiling UK room, then adjust for sunlight (south-facing rooms gain heat), the number of people (each adult adds heat), and ceiling height. It’s a guide, not a survey — when in doubt, size up.
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