Quick answer: A very sunny 5 m × 4 m room (20 m², 215 ft²) with a 3 m ceiling and three people needs about 6,000 × 1.23 × 1.1 + 600 = 8,720 BTU/h, about 0.73 tons — a 9,000 BTU split unit.
How it's calculated
The starting point is the ENERGY STAR room air conditioner chart, which gives a capacity for each range of floor area (about 20 BTU/h per square foot). The chart assumes 8 ft (2.44 m) ceilings; for a higher ceiling this calculator scales the chart figure by ceiling height ÷ 8 ft, because the room holds more air. Some calculators use a smooth BTU-per-area rule instead of the chart's steps, so their figure can differ by a few percent.
Then the ENERGY STAR adjustments: take off 10% for a heavily shaded room, add 10% for a very sunny one, add 600 BTU/h for each person over two who regularly uses the room, and add 4,000 BTU/h for a kitchen.
One ton of cooling is 12,000 BTU/h (3.517 kW). Split units in the Gulf are sold as 9,000, 12,000, 18,000, 24,000 BTU and up (0.75 to 2 tons or more). An oversized unit cools in short bursts and removes less humidity, so round up to the nearest size rather than far beyond.
Worked examples
- 5 m × 4 m, 3 m ceiling, very sunny, 3 people: 6,000 × 1.230 × 1.1 + 600 = 8,720 BTU/h (0.73 t)
- 16 ft × 13 ft (208 ft²), 8 ft ceiling, normal sun, 2 people: 6,000 BTU/h (0.5 t)
- Kitchen 4 m × 3 m (129 ft²), 2.4 m ceiling, normal: 5,000 + 4,000 = 9,000 BTU/h
ENERGY STAR sizing chart (8 ft ceiling)
| Floor area | BTU per hour |
|---|---|
| 100 – 150 ft² (9 – 14 m²) | 5,000 |
| 150 – 250 ft² (14 – 23 m²) | 6,000 |
| 250 – 300 ft² (23 – 28 m²) | 7,000 |
| 300 – 350 ft² (28 – 33 m²) | 8,000 |
| 350 – 400 ft² (33 – 37 m²) | 9,000 |
| 400 – 450 ft² (37 – 42 m²) | 10,000 |
| 450 – 550 ft² (42 – 51 m²) | 12,000 |
| 550 – 700 ft² (51 – 65 m²) | 14,000 |
| 700 – 1000 ft² (65 – 93 m²) | 18,000 |
| 1000 – 1200 ft² (93 – 111 m²) | 21,000 |
| 1200 – 1400 ft² (111 – 130 m²) | 23,000 |
| 1400 – 1500 ft² (130 – 139 m²) | 24,000 |
| 1500 – 2000 ft² (139 – 186 m²) | 30,000 |
| 2000 – 2500 ft² (186 – 232 m²) | 34,000 |
Frequently asked questions
How many tons of AC do I need for a 20 m² room?
About 6,000 BTU/h (0.5 ton) by the ENERGY STAR chart with a standard ceiling and normal sun; a sunny room with a high ceiling and three people needs about 9,000 BTU/h (0.75 ton).
What is one ton of air conditioning?
12,000 BTU per hour, the heat needed to melt one short ton of ice in 24 hours. It equals about 3.5 kW of cooling.
Is a bigger AC better?
No. An oversized unit switches on and off often, leaves the room clammy because it removes less moisture, and wastes energy.
Does this work for a whole villa?
It sizes one room at a time. For a whole house or open-plan spaces over 232 m², an engineer should do a heat-load calculation (for example ASHRAE or ACCA Manual J).
How much electricity does an air conditioner use?
Roughly its cooling capacity divided by its efficiency. An 18,000 BTU (1.5-ton) split unit with an EER around 10 pulls about 1.8 kW while the compressor runs. The electricity cost calculator turns that into a monthly bill.
Does a top-floor room need a bigger unit?
Often. A room under a roof baking in the sun, or with big west-facing windows, picks up a lot more heat. Pick the sunny option, and if you land between two sizes, go for the larger one.