BTU Calculator (Air Conditioner Size)
Estimate the air conditioner size a room needs.
Sizing an air conditioner
A common rule of thumb is about 20 BTU per hour for each square foot of floor space, adjusted for tall ceilings, sunlight, extra people and heat sources such as a kitchen. One ton of cooling equals 12,000 BTU per hour.
Example
With the starting values shown (Room area 300 sq ft; Ceiling height 8 ft; Sunlight Average; Number of people 2; Is it a kitchen? No), Cooling needed comes out as 6,000. Other results include in tons of cooling: 0.5; in kilowatts: 1.76.
An air conditioner that is too small will run constantly, and one that is too large will cool the room quickly but remove little humidity. For a whole house, or a hot climate, an HVAC professional should run a proper load calculation.
Frequently asked questions
What is a BTU?
A British thermal unit, a measure of heat. Air conditioners are rated in BTU per hour.
Can I round to the next size?
Air conditioners come in set sizes, so choose the nearest size above your result, but not far above it.
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