Air Conditioner BTU Calculator
Find the right cooling capacity for a room — in BTU and kW — and the AC size to buy.
Last reviewed 2026-06-06
Buy an air conditioner that’s too small and it runs flat-out yet never cools; too big and it blasts cold then shuts off, leaving the room humid. Matching the BTU rating to the room is what gets it right.
Enter the room size and a few conditions — sun, how many people use it, and whether it’s a kitchen — and we estimate the cooling capacity in BTU and kW, then suggest a standard unit size.
How to use the Air Conditioner BTU Calculator
- Measure the room length and width.
- Pick the sun exposure and how many people are usually in the room.
- Say whether it’s a kitchen (cooking adds a lot of heat).
- Read the BTU figure and the suggested AC unit size.
Frequently asked questions
What size air conditioner do I need for a room?
A common rule is about 20 BTU per square foot of floor area, adjusted for sun, occupancy and heat sources. A 180 sq ft room needs roughly 3,600 BTU baseline; the calculator refines this and suggests a standard unit size.
How many BTU is 1 kW of cooling?
About 3,412 BTU per hour equals 1 kW. So a 12,000 BTU air conditioner is roughly 3.5 kW of cooling capacity. The calculator shows both figures.
Is a bigger air conditioner always better?
No. An oversized unit cools the air quickly then switches off before it removes humidity, leaving the room cold and damp, and it wears out faster from short-cycling. Sizing it correctly is more comfortable and efficient.
What adds to the BTU requirement?
Strong sun, high ceilings, lots of people, kitchens, and hot climates all increase the load. This calculator adds for sun, extra occupants and kitchen heat; add more for very high ceilings or extreme heat.