How many BTU do I need for my room?
Short answer
The base rule is 200 BTU per square metre (50 frigorías) in a normal room: 9000 BTU for 45 m², 12,000 BTU for 60 m². Add 20-30% if the room gets direct sun, has large windows, an uninsulated roof, or is on the top floor.
It’s the first question anyone buying an air conditioner asks, and the one most often answered badly. The short answer is a simple rule; the useful answer is that rule plus a couple of corrections that change the result quite a bit.
The base rule
200 BTU per square metre (50 frigorías), for a room with standard ceiling height (2.5 m) and normal conditions.
| Floor area | Frigorías | BTU |
|---|---|---|
| Up to 20 m² | 1100 | 4400 |
| 20 to 30 m² | 1500 | 6000 |
| 30 to 45 m² | 2250 | 9000 |
| 45 to 60 m² | 3000 | 12,000 |
| 60 to 80 m² | 4500 | 18,000 |
| 80 to 100 m² | 6000 | 24,000 |
The corrections that actually matter
The base rule assumes an average room. Add 20 to 30% more if your case includes any of these:
- Direct sun for much of the day, especially west or north-facing
- Large windows or glass without heavy curtains or film
- Top floor or uninsulated roof (a metal roof or exposed slab changes the maths enormously)
- High ceilings, above 2.8 m
- Lots of people or equipment: an office with six people and computers generates real heat
- Kitchen open to the living room, because the oven and hob add heat
And you can subtract a little if the room sits between other conditioned rooms, is well insulated, or gets almost no sun.
A worked example
A 40 m² living-dining room, upstairs, with a west-facing picture window that catches sun all afternoon.
- Base: 40 m² × 50 = 2000 frigorías
- Top floor + west window: +30% = 2600 frigorías
- Nearest commercial size upward: 3000 frigorías (12,000 BTU)
Without the corrections, the raw calculation would have given 2000 and you’d have bought a 2250 that gives up at five in the afternoon in January.
Why “playing it safe” with a bigger unit backfires
Buying considerably more capacity than you need looks prudent, but works against you:
- It cycles constantly: cools fast, cuts out, starts again. Every start is the moment of highest wear and consumption.
- It doesn’t dehumidify: the unit needs to run a sustained stretch to pull moisture out of the air. If it cuts out immediately, the room ends up cold but damp — that unpleasant heavy-air feeling.
- It costs more, to buy and to install.
The right size — the unit that runs long, gentle cycles — is what delivers the best comfort and the lowest consumption. If you’re between two sizes and your room has the factors above, go up; if it doesn’t, stay with what the calculation gives.
Inverter: doesn’t change the sizing, changes the running cost
An inverter unit modulates compressor output instead of switching on and off, so it holds temperature with far less consumption and no start-up spikes. It doesn’t change the capacity you need, but it is much more forgiving of oversizing, and it’s the technology worth paying for if you’ll run the unit for many hours.
Frequently asked
BTU or frigorías? How do they convert?
They're two units for the same thing and both are used in Argentina. The equivalence is that 1 frigoría is roughly 4 BTU. So a 3000 frigoría unit is also sold as 12,000 BTU, and a 2250 frigoría one as 9000 BTU. They're the same machines: if one listing shows BTU and another shows frigorías, divide the BTU by 4 and you're comparing like with like.
What happens if I buy a bigger unit than I need?
Counterintuitively, it's a problem rather than a safety margin. An oversized unit cools the room very fast and cuts out, then starts again, over and over. That constant cycling wears the compressor, uses more energy than it should and, above all, doesn't dehumidify: the air ends up cold but heavy and damp — that basement feeling. A correctly sized unit runs longer, gentler cycles, dries the air and gives far better comfort. On an inverter the problem is smaller because it modulates output, but paying for capacity you'll never use still makes no sense.
Can one unit cool the whole house?
Generally no, and it's the most common sizing mistake. An air conditioner cools the room it's in: cold air doesn't turn down hallways or climb stairs on its own. If you want to condition several rooms, either put a unit in each (multi-split) or go to a ducted system. Buying an enormous unit for the living room hoping it will also cool the bedrooms ends in the worst of both worlds: a freezing, damp living room and bedrooms that are still hot.
Ready to choose?
These are the guides with real products and verified prices that match this question.
The figures in this note are based on the products' public specifications. How we do it. See all questions →
