BTU Calculator
Based on the Energy Star room air conditioner sizing guide's square-footage table, with its standard adjustments for sun exposure, extra occupants, and kitchens. An oversized unit cools fast but cycles on/off too often to properly remove humidity — bigger isn't automatically better.
Free BTU calculator for sizing a room air conditioner — based on the Energy Star sizing guide's square-footage table, adjusted for sun exposure, occupants, and kitchens.
How it works
- Enter the room's square footage and how many people usually use it
- Set the sun exposure, and check the box if it's a kitchen
- See the recommended cooling capacity in BTU
Frequently asked questions
Where do these numbers come from?
The base figures come from the Energy Star room air conditioner sizing guide's published square-footage table, not a made-up linear formula — real cooling capacity needs don't scale in a straight line with area. The sun exposure, occupant, and kitchen adjustments are Energy Star's own standard corrections.
Why not just buy the biggest unit I can find?
An oversized air conditioner cools the room quickly but shuts off before it can properly remove humidity, cycling on and off repeatedly — leaving the room feeling cold and clammy rather than actually comfortable.
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Update history
- 2026-09-01 Launched: BTU calculator using the Energy Star sizing table with sun exposure, occupant, and kitchen adjustments. Entirely client-side.