Air Conditioner BTU Calculator by Room Area

Sizing AC capacity by area, occupants and appliances

The rule most installers use for homes is 600 BTU/h per m², plus 600 per extra person (anyone past the 2nd) and 600 per active electronic appliance in the room (TV, computer, a fridge). Say you have 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. That rounds up to a commercial 12,000 BTU/h unit, or 18,000 if you want headroom. Add 20% when ceilings run high (> 2.8 m), and another 20% when the room takes west-facing sun exposure. Standard capacities sold in Brazil are 7,500 / 9,000 / 12,000 / 18,000 / 24,000 / 30,000 BTU/h.

Applications and energy efficiency

People use this to pick units at Casas Bahia, Magazine Luiza or Fast Shop, and to pre-size residential and small commercial installs before the electrician shows up. Efficiency comes down to the EER/COP rating, and split inverter compressors modulate their output, which can cut energy use by up to 40% versus fixed-speed models. Check for the Procel seal (INMETRO); class A is the most efficient tier. An undersized unit never stops running, while an oversized one cycles too fast and barely pulls humidity out of the air.

FAQ

Is it better to oversize for safety? No. An oversized AC switches on and off too quickly, which leaves the room muggy and burns energy for nothing. Go for a unit that lands at the calculated BTU, or just a notch above it.

Does ceiling height matter? Yes. The 600 BTU/m² figure assumes ceilings around 2.5–2.8 m. Once you go higher, tack on roughly 20% more capacity.

Inverter or conventional? Inverter splits cost more at the register, but the lower power bills usually pay that back within 2–3 years. They also hold a steadier temperature and run quieter.