BTU Calculator for Heating/Cooling
Air conditioner/heater capacity by room size.
Tip: Quick rule: ~20 BTU per ft² or ~7,000 BTU for a 10 m² room.
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About this digital tool
The BTU calculator for heating and cooling helps you choose the right capacity of air conditioner or heater for a room. Enter the length, width and height of the room, choose the quality of insulation and sun exposure, and get the capacity in BTU/h and kW.
The calculation starts from the room's volume (m³) and multiplies it by a base coefficient of 42, by the insulation factor (0.7 for good, 1.0 average, 1.5 poor) and by the exposure factor (from 1.0 to 1.1). The result is converted to kW by dividing by 3412 and the tool suggests the nearest air-conditioner size, such as 9000, 12000, 18000 or 24000 BTU. It is a practical estimate for buying, not a full thermal design.
How to use
- Enter the room area (m²) and the height.
- Choose the insulation and the sun exposure.
- See the recommended capacity in BTU.
Frequently asked questions
How is BTU converted to kW?
1,000 BTU/h ≈ 0.293 kW. E.g. a 12,000 BTU air conditioner ≈ 3.5 kW.
How many BTU are needed for a 20 m² room?
It depends on height, insulation and exposure. With a height of 2.7 m, average insulation and neutral exposure it comes to about 2268 BTU/h, and the tool suggests the nearest air conditioner. Enter your room's details for an exact result.
What affects the capacity of an air conditioner?
The room volume, the insulation of walls and windows, sun exposure, the number of people and heat-producing appliances. The tool takes volume, insulation and exposure into account; for rooms with many appliances add a little capacity.
Is it good to buy an air conditioner bigger than the result?
A big surplus is not recommended. An oversized unit cycles on and off often, uses more energy and doesn't remove humidity well. Choose the standard size closest to the result.