BTU Calculator
Find the right BTU for your room — for air conditioners or heaters.
Room Details
What is the BTU Calculator?
The BTU (British Thermal Unit) Calculator helps homeowners and HVAC technicians size air conditioners and heaters. If you buy a unit with too few BTUs, it won't cool the room; if it has too many BTUs, it will short-cycle and leave the air feeling clammy.
How It Works (Formula)
The tool multiplies the square footage of the room by a baseline cooling factor (typically 20 BTUs per square foot). It then adds adjustments for ceiling height, sun exposure, and the number of people occupying the room.
$$ \text{Base BTUs} = \text{Room Area (sq ft)} \times 20 $$
Add 600 BTUs for each additional person regularly in the room.
How to Use It
Enter the dimensions of the room you want to cool or heat. Select your insulation quality and sun exposure. The calculator will output the exact BTU rating you should look for when buying a window AC, mini-split, or furnace.