What Size Air Conditioner Do I Need? BTU by Room Size
Published: May 23, 2026
Picking the right cooling capacity matters for two reasons: too small and it never cools the room; too big and it wastes energy and leaves the air humid. Capacity is measured in BTU (British Thermal Units per hour) — the higher the BTU, the more cooling power.
Prefer to skip the maths? Use our interactive BTU calculator to get a recommendation for your exact room.
Quick BTU sizing chart
A practical starting point for a standard room (average insulation, ~2.4 m ceilings):
| Room size | Approx. BTU |
|---|---|
| Up to 15 m² (160 sq ft) | 5,000–6,000 |
| 15–25 m² (160–270 sq ft) | 7,000–9,000 |
| 25–35 m² (270–375 sq ft) | 10,000–12,000 |
| 35–50 m² (375–540 sq ft) | 12,000–14,000 |
| 50–70 m² (540–750 sq ft) | 14,000–18,000 |
The rule of thumb behind the chart: roughly 350–450 BTU per square metre (about 20 BTU per square foot).
Adjust for your room
Add capacity if your room:
- Gets direct afternoon sun (+10–20%).
- Has high ceilings or is open-plan.
- Is a kitchen or has heat-producing appliances (+10–15%).
- Is regularly occupied by several people.
Take a little off for a heavily shaded or well-insulated room.
Don’t oversize
An oversized air conditioner reaches the target temperature fast, then switches off before it has removed much humidity — so the room feels cold and damp, the compressor short-cycles, and you pay for electricity you didn’t need. Matching BTU to room size keeps both comfort and running cost in check.
BTU vs running cost
More BTU means more electricity. That’s why it pays to buy the smallest unit that comfortably cools your room, then compare those units by what they cost to run. See our running-cost guide, or jump straight to every unit ranked by cost to run.
