About the BTU Calculator
BTU per hour is the standard way air conditioners and heaters are rated. The base figure comes from room volume, then adjustments for sun exposure, insulation quality, glazing and the number of people give a realistic sizing. Undersizing leaves the room uncomfortable; oversizing short-cycles and wastes energy.
Also known as: btu calculator for room, air conditioner size, how many btu do i need, heating btu, cooling btu.
How to use this calculator
- Enter room length, room width, ceiling height, purpose and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
BTU/h = volume × base load × sun × insulation + occupant and window loads
Worked example
Using the values pre-filled in the calculator above:
- Room length = 5 m
- Room width = 4 m
- Ceiling height = 2.5 m
- Purpose: Cooling
- Sun exposure: Average
- Insulation: Average
- People normally in the room = 2
- Number of windows = 2
the calculator returns:
- BTU required: 6,328 BTU/h
- Recommended unit size: 7,000 BTU/h
- In kilowatts: 1.854
- Air conditioner tonnage: 0.53 tons