About this calculator
Quick sizing for a wall split aircon in BTU for one room, rounded up to a size you can buy.
How it’s calculated
BTU = floor area (m²) × 500, the rule of thumb Builders gives for South African homes with ceilings 2.5 to 3 m high. The result is rounded up to the next wall split size (9,000, 12,000, 18,000, 24,000, 30,000 or 36,000 BTU), and one size more where the room has extra heat: big sunny windows, lots of people or appliances, poor ceiling insulation or a double-volume ceiling.
Worked example
With these inputs:
- Room length
- 4.5 m
- Room width
- 3.8 m
- Big sunny windows, a busy room, lots of appliances, poor ceiling insulation or a double-volume ceiling
- No
the result is:
- Cooling capacity
- 8,550 BTU/h
- Room area
- 17.1 m²
- Rate
- 500 BTU per m²
- In kW
- 2.5
Tips from the trade
- Oversized AC short-cycles and leaves rooms clammy, so bigger is not better.
- Open-plan areas count as one room. Measure the whole space the unit has to cool, not just the part it faces.
Common questions
What size aircon for a 20 m² room?
About 10,000 BTU (20 × 500), so a 12,000 BTU wall split. Go up to 18,000 BTU if the room gets a lot of sun or has a double-volume ceiling.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.