❄️ BTU Calculator
Work out what size air conditioner or heater you need for a room – in BTU per hour, tons and kilowatts.
Quick answer: Cooling BTU/h ≈ room area (sq ft) × 20, adjusted for ceiling height, sun, people and climate. A 400 sq ft room with 8 ft ceilings in a temperate climate needs about 8,000 BTU/h (0.67 tons, 2.34 kW) – an 8,000 BTU air conditioner.
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BTU Calculator inputs
Result
Air conditioner size needed
8,000 BTU/h
0.67 tons · 2.34 kW
| Base load (400 sq ft) | 8,000 BTU/h |
| Cooling needed | 8,000 BTU/h |
- Recommended unit
- 8,000 BTU/h
- Tons of cooling
- 0.67
- Kilowatts
- 2.34 kW
- Per unit area
- 20 BTU/h per sq ft
Standard unit sizes for your conditions
| Unit size | Tons | Kilowatts | Room up to |
|---|---|---|---|
| 5,000 BTU/h | 0.42 | 1.47 kW | 250 sq ft |
| 6,000 BTU/h | 0.5 | 1.76 kW | 300 sq ft |
| 8,000 BTU/h ✓ | 0.67 | 2.34 kW | 400 sq ft |
| 10,000 BTU/h | 0.83 | 2.93 kW | 500 sq ft |
| 12,000 BTU/h | 1 | 3.52 kW | 600 sq ft |
| 14,000 BTU/h | 1.17 | 4.1 kW | 700 sq ft |
| 18,000 BTU/h | 1.5 | 5.28 kW | 900 sq ft |
| 24,000 BTU/h | 2 | 7.03 kW | 1,200 sq ft |
| 30,000 BTU/h | 2.5 | 8.79 kW | 1,500 sq ft |
| 36,000 BTU/h | 3 | 10.55 kW | 1,800 sq ft |
| 48,000 BTU/h | 4 | 14.07 kW | 2,400 sq ft |
| 60,000 BTU/h | 5 | 17.58 kW | 3,000 sq ft |
Room sizes use your ceiling height, climate, sun exposure, occupants and kitchen settings. Rules of thumb – for whole homes, ask an HVAC professional for a Manual J load calculation.
How to size an air conditioner or heater
Measure the room’s length and width, multiply to get the area, then enter the ceiling height and the conditions. The calculator uses widely used rules of thumb for single rooms.
Cooling BTU/h = area (sq ft) × 20 × (ceiling ÷ 8 ft) × climate × sun + 600 per person above 2 + 4,000 for a kitchen
Heating BTU/h = area (sq ft) × 20–50 (by climate) × (ceiling ÷ 8 ft) × sun · 1 ton = 12,000 BTU/h · 1 BTU/h = 0.293 W
Worked example
A 400 sq ft (37 m²) living room with 8 ft ceilings, average sun, two people and a temperate climate: 400 × 20 = 8,000 BTU/h, which is 0.67 tons or 2.34 kW – an 8,000 BTU unit. The same room in Dubai or Riyadh (× 1.5) needs 12,000 BTU/h, a 1-ton unit; add 600 BTU/h for every extra person and 10% if it gets strong afternoon sun.
Adjustment factors
| Factor | Cooling adjustment |
|---|---|
| Cold climate | × 0.85 |
| Warm climate | × 1.1 |
| Hot & humid climate | × 1.25 |
| Very hot (Gulf / desert) | × 1.5 |
| Very sunny room / heavily shaded | +10% / −10% |
| Each person above two | +600 BTU/h |
| Kitchen | +4,000 BTU/h |
Common AC sizes
| BTU/h | Tons | kW | Room (temperate) |
|---|---|---|---|
| 6,000 | 0.5 | 1.76 | up to 300 sq ft (28 m²) |
| 9,000 | 0.75 | 2.64 | up to 450 sq ft (42 m²) |
| 12,000 | 1 | 3.52 | up to 600 sq ft (56 m²) |
| 18,000 | 1.5 | 5.28 | up to 900 sq ft (84 m²) |
| 24,000 | 2 | 7.03 | up to 1,200 sq ft (111 m²) |
Tips
- Poor insulation, large west-facing windows or top-floor rooms under a hot roof need 10–20% more capacity.
- For open-plan spaces, add the areas of connected rooms that share the air.
- Inverter units run efficiently over a wide range, so slight oversizing is less of a problem than with fixed-speed units.
Frequently asked questions
How many BTU do I need per square foot?
About 20 BTU/h per square foot of floor area for cooling a room with 8 ft ceilings in a temperate climate – roughly 215 BTU/h per m². Hot climates need 25–30 BTU/h per sq ft or more.
How many square feet does a 12,000 BTU air conditioner cool?
Around 500–600 sq ft (46–56 m²) in a temperate climate with average sun and 8 ft ceilings, but only about 400 sq ft (37 m²) in a very hot Gulf climate.
What is a ton of air conditioning?
One ton of refrigeration is 12,000 BTU per hour (about 3.5 kW) – the cooling from melting one short ton of ice in 24 hours. A 1.5-ton split AC is 18,000 BTU/h.
What size AC do I need in the UAE or Saudi Arabia?
Choose the “very hot (Gulf / GCC)” climate. It applies a 1.5× factor, giving about 30 BTU/h per sq ft (≈ 320 BTU/h per m²), so a 20 m² bedroom needs roughly 6,500–7,000 BTU/h – a 0.75-ton or 1-ton split unit.
Is a bigger air conditioner better?
No. An oversized unit cools the room quickly then switches off before removing humidity, leaving it clammy and wasting energy. Choose the nearest standard size at or just above the calculated load.