Guide
What Size Air Conditioner Do I Need? BTU by Room Size
The 20-BTU rule, the adjustments that matter, and why bigger is not better.
Updated September 2026
Start with 20 BTU per square foot
A good baseline for a room air conditioner is about 20 BTU per square foot of floor space. A 12 × 14 room is 168 sq ft, so roughly 3,400 BTU before adjustments — which rounds to a common 5,000 BTU unit.
Try it AC BTU Calculator → Size a room air conditioner in BTU from the room size, sun exposure and occupants — and see the unit size to buy.Adjust for sun, people and kitchens
The rule of thumb shifts with the room:
- Very sunny room: add about 10%.
- Heavily shaded room: subtract about 10%.
- More than two people regularly in the room: add ~600 BTU per extra person.
- Kitchen: add about 4,000 BTU for the appliances.
Why bigger isn't better
An oversized AC cools the air fast but shuts off before it removes humidity, leaving the room cold and clammy and short-cycling the compressor. Right-sizing runs longer, dehumidifies properly and uses less energy. Use the number our calculator gives you rather than rounding way up.
FAQ
How many BTU for a 12x14 room?
About 3,400 BTU by the 20-BTU-per-sq-ft rule — a 5,000 BTU unit — adjusted up for a sunny room, extra people or a kitchen.
Is a bigger AC better?
No. An oversized unit short-cycles and leaves the room humid. Match the BTU to the room for comfort and efficiency.
Does sun exposure change the size?
Yes — add about 10% for a very sunny room and subtract about 10% for a shaded one.