BTU Calculator
Estimate the BTU capacity a room needs from its size.
Size the AC to the room
Air conditioners and heaters are rated in BTUs, and matching the capacity to the room matters: too small and it never keeps up, too large and it cools without removing humidity. A square-footage rule gets you close.
Enter the room dimensions and it estimates the BTUs needed at about 20 per square foot, adjusting for sun exposure and extra occupants. A 15 by 12 foot room needs roughly 3,600 BTU before adjustments.
Useful and private
The estimate is computed in your browser, so nothing you enter is uploaded.
Frequently Asked Questions
What is a BTU?
A British Thermal Unit measures heating and cooling energy. Air conditioners and heaters are rated by how many BTUs per hour they move.
How is the estimate made?
It uses about 20 BTU per square foot as a baseline, then adjusts for sunny rooms and how many people use the space.
Is bigger always better?
No. An oversized air conditioner cools too fast to remove humidity, leaving the room clammy. Match the capacity to the room.
Browse the full set of free, private, in-browser tools.