BTU calculator
Estimate the BTU per hour of cooling a room needs, with adjustments for sun, people, ceiling height and kitchens.
About this calculator
Enter the room area and ceiling height, then choose how sunny the room is and how many people use it. A kitchen adds heat from cooking, so tick the box if that applies.
The result is a guide to unit size. Windows, insulation and climate matter, so ask an installer for a final recommendation.
Measurements and terms explained
- BTU
- British thermal unit. The heat needed to warm one pound of water by one degree Fahrenheit.
- BTU/h
- BTU per hour, the rate a unit heats or cools. Air conditioners are sized this way.
- Ton of cooling
- 12,000 BTU/h, about 3.5 kW.
- Ceiling height
- Taller rooms hold more air, so need more cooling than a standard 8 ft (2.4 m) room.
Common questions
How many BTU per square foot?
A common rule is about 20 BTU an hour for each square foot of floor, then adjusted for the room.
How many kW is that?
Divide BTU per hour by 3,412 to get kilowatts.
More free calculators
Concrete calculator
Volume and bags of concrete for a slab.
Square footage calculator
Area of a room, plot or shape in any unit.
Stair calculator
Steps, riser height and stringer length for a staircase.
Roofing calculator
Roof area, squares and shingle bundles from pitch.
Tile calculator
How many tiles and boxes you need for a floor or wall.
Mulch calculator
Cubic yards, metres and bags of mulch for a bed.