Free tool
What size air conditioner do I need?
Air conditioners are rated in BTU (British Thermal Units). Too small and it'll run flat out without cooling; too big and it wastes energy. Enter your room and we'll estimate the capacity to look for.
You should look for around
8,000 BTU
≈ 2.3 kW cooling · 9,000 BTU class unit
How the estimate works
We start from roughly 400 BTU per m² of floor area — a widely used rule of thumb for UK rooms with standard ceilings — then adjust for sunlight, the number of people (each person adds heat), and whether it's a kitchen (appliances add a lot). For an exact figure, a heat-load survey from an installer is the gold standard, especially for fixed split systems.
Rough guide by room
- Small bedroom / office (up to 15 m²): ~5,000–7,000 BTU
- Average bedroom / living room (15–30 m²): ~7,000–12,000 BTU
- Large living room / open plan (30–45 m²): ~12,000–18,000 BTU
This tool gives a ballpark for guidance only and isn't a substitute for professional advice.