What Size AC Do I Need for a Room?
A quick room-by-room BTU estimate for a window unit or a ductless mini-split — useful for a garage, sunroom, addition, or a single hot room.
A rough starting point is about 20 BTU per square foot, adjusted up for a sunny room, extra occupants, or high ceilings, and up again for Florida humidity.
Why this matters
Use this to right-size a window unit or mini-split for one room before buying — undersizing leaves it humid, oversizing short-cycles.
The public-safe rule
This page gives an educational planning result. Final quote, rebate, payment, package, and installer details wait until the customer and home record are saved inside the assessment flow.
Start exact assessmentRun the numbers.
About 8,000 BTU for this room
For a 300 sq ft room with average sun, plan around a 8,000 BTU window unit or ductless mini-split.
Recommended size
8,000 BTU
Estimated load
6,300 BTU
Room area
300 sq ft
Best fit
Window or mini-split
This is a single-room estimate using the ~20 BTU/sq ft rule with adjustments for sun, occupancy, ceiling height, and Florida humidity. A whole-home system is sized differently (Manual J).
For a converted garage, sunroom, or addition, a ductless mini-split usually beats a window unit on comfort, humidity, and efficiency.
Don't oversize: a too-big room unit cools fast but leaves the room humid and short-cycles.
This is a planning estimate, not a final quote or engineering report. Field conditions, permits, equipment selection, ducts, electrical work, and installer verification can change the result.
How this estimate is grounded.
The visible result, assumptions, and schema match. Structured data does not claim anything that is not also shown on the page.