Air conditioner BTU calculator
Enter the room size and a few details about it. You’ll get the BTU rating to shop for and the nearest standard unit size.
Cooling capacity
6,000 BTU/hr
- Look for a unit of
- 6,000 BTU (0.5 tons)
- Room size
- 180 sq ft
- Chart starting point
- 6,000 BTU/hr
How it works
The starting point is the room air conditioner sizing chart published by Energy Star, which matches square footage ranges to a BTU rating. The calculator then applies Energy Star’s adjustments: 10% less for a heavily shaded room, 10% more for a very sunny one, 600 BTU for each regular occupant beyond two, and 4,000 BTU if the room is a kitchen.
It then rounds up to the next common unit size you’ll actually find on a store shelf.
Example
With room length 15 ft, room width 12 ft, sun exposure: average, people who regularly use the room 2, is it a kitchen: no, the answer is 6,000 BTU/hr.
Tips before you buy
- Bigger isn’t better. An oversized unit cools the room fast and shuts off before it removes much humidity, leaving the room cold and clammy.
- Ceilings over 8 feet, poor insulation or a hot, humid climate can push you up a size. Lots of shade and good insulation can pull you down.
- For a whole house or central system, get a professional load calculation (Manual J) rather than using a room chart.
- One “ton” of cooling is 12,000 BTU per hour.
Common questions
What size air conditioner do I need for a 500 sq ft room?
12,000 BTU per Energy Star’s chart, before adjustments for sun, people or a kitchen.
What size AC for a 12×12 bedroom?
144 square feet calls for 5,000 BTU on the chart. A very sunny room or more than two occupants may need the next size up.
How many BTU is a ton of air conditioning?
12,000 BTU per hour. A 24,000 BTU unit is a 2-ton unit.