What Aircon HP Do I Need for My Room?
Most sizing charts use floor area alone. This one also accounts for ceiling height, sun exposure and how many people use the room — the three things that most often make a "correct" size feel wrong.
Buying an air conditioner by floor area alone is the reason so many rooms end up either clammy or never quite cool. A 16 m² bedroom under a shaded wall and a 16 m² top-floor room with west-facing glass need noticeably different machines, even though the chart in the shop gives them the same answer.
How the Calculation Works
The base figure is floor area multiplied by 500 BTU/hr per square metre, which is the planning rule used across most of Southeast Asia for residential rooms. Three adjustments are then applied:
- Ceiling height. The rule assumes 2.7 m. A room with a 3.5 m ceiling holds far more air to cool, so the load scales with the actual height.
- Sun exposure. West-facing glass, a top-floor position or a metal roof can add 15–30% to the heat load. A shaded room subtracts about 10%.
- Occupancy. Each person adds roughly 600 BTU/hr of body heat. The base rule already assumes two people, so only additional occupants are counted.
The result is rounded up to the nearest size actually manufactured. Rounding up rather than down matters: a unit running slightly oversized simply cycles a little more, while an undersized one never reaches temperature at all on the hottest days.
Aircon Size by Room Area
These are baseline figures at 2.7 m ceiling height, average sun and two occupants — the same assumptions behind the shop charts. Use them as a sanity check on the calculator above.
| Floor area | Approx. sq ft | BTU/hr needed | Aircon size | Tons |
|---|---|---|---|---|
| Up to 10 m² | up to 110 | 5,000 | 0.5 HP | 0.42 |
| 10–14 m² | 110–150 | 7,000 | 0.75 HP | 0.58 |
| 14–18 m² | 150–195 | 9,000 | 1.0 HP | 0.75 |
| 18–24 m² | 195–260 | 12,000 | 1.5 HP | 1.00 |
| 24–36 m² | 260–390 | 18,000 | 2.0 HP | 1.50 |
| 36–48 m² | 390–515 | 24,000 | 2.5 HP | 2.00 |
| 48–60 m² | 515–645 | 30,000 | 3.0 HP | 2.50 |
What Pushes You to the Next Size Up
Floor area sets the baseline, but these conditions routinely add enough load to justify the next model up:
- Top floor or metal roof. Roof heat gain is the single biggest factor in tropical homes and can add close to a third to the load.
- Large or west-facing windows. Afternoon sun through unshaded glass behaves like a small heater running all day.
- Kitchens and cooking areas. Appliance heat is substantial and is not covered by any per-square-metre rule.
- More than two regular occupants. Living rooms and offices frequently exceed the assumption the base rule is built on.
- Poor insulation or an uninsulated ceiling. Common in older buildings and often overlooked entirely.
Why Bigger Is Not Safer
An oversized air conditioner reaches the set temperature quickly and then switches off — before it has run long enough to pull moisture out of the air. The room ends up cold but humid, which feels clammy rather than comfortable. The compressor also short-cycles, turning on and off repeatedly, which wastes electricity and shortens its working life.
This is why sizing correctly beats sizing generously. If your calculated figure sits between two model sizes, the sensible move is to take the larger one only when the room has a genuine additional heat source — not as a default insurance policy.
Converting the Answer to Other Scales
Once you have a BTU figure, translating it is straightforward. Retailers in the Philippines and Malaysia will quote horsepower; Indian and Middle Eastern suppliers will quote tons; European and Japanese datasheets use cooling kW. Our BTU to HP calculator covers the first, ton to HP the second, and cooling kW to HP the third. If the listing you're comparing uses the colloquial "tonner", our tonner to HP chart maps it directly.
Frequently Asked Questions
A 16 m² room with a standard 2.7 m ceiling and average sun needs about 8,000 BTU/hr — a 1 HP unit. Add west-facing glass or a top-floor position and it moves to 1.5 HP.
Around 500 BTU/hr per square metre for a residential room with a 2.7 m ceiling and moderate sun. High heat-gain rooms need more, and the rule does not cover kitchens or server rooms.
A 1 HP unit delivers about 9,000 BTU/hr, suiting roughly 14–18 m² under average conditions — closer to 14 m² in a hot, sunny or top-floor room.
Neither. Oversized units cool fast then shut off before removing humidity, leaving the room cold and clammy while the compressor short-cycles. Undersized units run constantly without reaching temperature. Size to the calculated load.
Yes, significantly. The standard rule assumes a 2.7 m ceiling. A 3.5 m ceiling means about 30% more air to cool and needs a correspondingly larger unit.
Divide square feet by 10.764. A 200 sq ft room is about 18.6 m², needing roughly 9,300 BTU/hr — a 1 HP unit.
Yes. Cooking appliances add a large heat load no per-square-metre rule accounts for. Kitchens typically need at least one size above what floor area suggests.