About

BTU Calculator is a free tool that estimates how much cooling or heating power a room needs, in BTU per hour. Enter the room's size and a few details — ceiling height, sun exposure, occupants, and whether it's a kitchen — and it suggests both a recommended capacity and the nearest standard air conditioner size.

It was built for homeowners and renters trying to buy the right-sized window unit, mini-split, or heater without wading through sales pages. The calculator runs entirely in your browser — nothing you enter is uploaded or stored.

How the estimates are made

Cooling uses the widely cited baseline of about 20 BTU per square foot, scaled for ceiling height and adjusted for sun, occupants, and kitchens. Heating uses a climate-based range of roughly 30–60 BTU per square foot. These are guidelines; insulation, windows, and local climate all affect real-world needs, so use the results as a starting point.

Questions or suggestions? See the contact page.