Air Conditioner BTU Calculator
The Air Conditioner BTU Calculator estimates the cooling capacity (in BTU/hr) needed to cool a room, based on its dimensions, climate, sun exposure and number of occupants. It also converts the result into tonnes of cooling and kilowatts.
Formula
BTU = Length × Width × Height × 300 × ClimateFactor × SunFactor + (Occupants−2) × 600
- Room dimensions are entered in metres; the base load is about 300 BTU per cubic metre of space.
- Climate factor scales the load (mild 0.8, hot 1.0, very hot 1.2) and sun exposure adjusts it (shaded 0.9, average 1.0, sunny 1.1).
- Each occupant beyond the first two adds about 600 BTU/hr.
- Results are converted to tonnes (BTU ÷ 12,000) and kilowatts for convenience. Treat this as a sizing estimate, not a substitute for a professional load calculation.
Example Calculation
Inputs
- Room Length: 5 m
- Room Width: 4 m
- Ceiling Height: 3 m
- Climate: hot
- Sun Exposure: average
- Occupants: 2
A 5 × 4 × 3 m room (60 m³) in a hot climate with average sun and 2 occupants needs about 60 × 300 × 1.0 × 1.0 = 18,000 BTU/hr, or roughly 1.5 tonnes of cooling.
Frequently asked questions
How many BTU do I need to cool a room?
Enter the room size, climate, sun exposure and occupants, and the calculator estimates the BTU/hr cooling capacity required.
How do BTU convert to tonnes?
One tonne of cooling equals 12,000 BTU/hr, so the calculator divides the BTU result by 12,000.
Why do climate and sun matter?
Hotter climates and sunnier rooms gain more heat, so they need proportionally more cooling capacity.
Why add BTU for occupants?
Each person gives off body heat, so rooms with more occupants need extra cooling — about 600 BTU/hr per person beyond the first two.
Is this a professional load calculation?
No. It is a quick sizing estimate. For precise sizing, a full Manual J or equivalent load calculation is recommended.