Air Conditioner Size Calculator
Enter the room, its size, the window orientation and the heat sources to get the cooling capacity in watts and BTU, plus the size class to buy — so the unit actually cools the room instead of running flat out.
Air conditioners are sold by "horsepower", but a unit is sized by cooling capacity in watts. Undersizing is the common mistake: the room never quite reaches the set temperature, the compressor never stops, and power use goes up rather than down. Enter the room and its conditions; the page returns the capacity you need and the size class that covers it.
Room conditions
Lengths in metres. Every field recalculates instantly.
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Cooling load by room type
| Room | Load | Typical use |
|---|---|---|
| Bedroom | 130 W/m² | Sleeping, door closed, two people |
| Living room | 150 W/m² | More people, more equipment, doors open |
| Kitchen | 200 W/m² | Stove and oven add heat while cooking |
Common size classes
- 1 hp — about 2300 W, up to 12 m²
- 1.5 hp — about 3200 W, up to 20 m²
- 2 hp — about 5000 W, up to 30 m²
- 3 hp — about 7200 W, up to 45 m²
Before you buy
- Match the nameplate cooling capacity, not the horsepower label. 1 hp means roughly 2300–2600 W of cooling, not 735 W.
- A west-facing room or a top-floor room needs one size up; the sun load and the roof heat are real, not marketing.
- An oversized unit cools fast but dehumidifies poorly, and the compressor short-cycles. Do not jump two sizes for safety.
- If the unit will run at night in a bedroom, prioritise a low minimum output over a high maximum.
- For an open-plan living and dining area, add the two areas and treat the result as one room.
Four common mistakes
- Sizing by floor area alone, ignoring a west window that adds 15 percent of load.
- Buying by the "1 hp per 10 m²" rule of thumb, which under-cools a modern living room.
- Mounting the indoor unit in the corner above a sofa, so cold air blows straight onto people and the far side stays warm.
- Forgetting the outdoor unit needs airflow — a sealed balcony or a tight service cage cuts capacity and causes summer shutdowns.
Reference values for ordinary homes in a temperate climate. Glass area, insulation and occupancy can shift the result; treat the figure as a starting point, not a guarantee.