BTU (AC) Calculator
Calculate the ideal BTU/h power for a room — based on area, people, electronics and sun exposure. Everything in your browser.
Sizing BTU/h for residential air conditioning
The residential rule of thumb runs 600 BTU/h per m², plus 600 per extra person beyond the 2nd, plus 600 per active electronic appliance in the room (TV, computer, fridge). Take a 20 m² living room with 4 people and 1 TV: 20·600 + 2·600 + 1·600 = 12,000 + 1,200 + 600 = 13,800 BTU/h, which rounds up to a commercial 12,000 BTU/h unit (or 18,000 if you want margin). Bump the figure up when you have high ceilings (> 2.8 m), west-facing sun exposure, or poor insulation. The standard capacities sold in Brazil are 7,500 / 9,000 / 12,000 / 18,000 / 24,000 / 30,000 BTU/h.
Applications and standards
People use this to spec units at Casas Bahia, Magazine Luiza or Fast Shop, and to pre-size a residential install. There are three types worth knowing: split is efficient and quiet, window is simple and cheap, and portable is a last resort with lower efficiency. Efficiency itself shows up as EER/COP, and inverter compressors draw less energy. Check for the Procel seal (INMETRO), where class A is the most efficient. An undersized unit runs nonstop, while an oversized one cycles too fast and barely dehumidifies.
FAQ
Is it better to oversize for safety? No. An oversized AC switches on and off too quickly, which leaves the room humid and wastes energy. Pick a unit that matches the calculated BTU or sits just above it.
Does ceiling height matter? Yes. The 600 BTU/m² rule assumes ceilings around 2.5–2.8 m. Go higher than that and you should add roughly 10–15% capacity for each extra meter.
Split vs window — which to choose? A split is quieter, more efficient and better looking, though it needs proper installation. A window unit costs less and you can fit it yourself, but expect more noise and lower efficiency. Portable units rarely earn their keep.
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How many BTUs for your room
An air conditioner that's too weak won't cool the room. One that's too strong burns energy for nothing and dehumidifies poorly on top of that. The balance lies in getting the BTU/h power right, and that's what this calculator estimates for your room, based on a few details you provide.
The math doesn't stop at floor area. It weighs how many people usually stay in the space, the electronics heating the place up, and sun exposure. That last detail shifts the result a lot: picture a bedroom always in the shade versus a living room that catches sun all afternoon. Add it all up and the BTU estimate reflects what the room needs far better.
The calculation happens in your own browser. Take it as a practical reference when picking a unit, before you pay for power that's more or less than you need.