What is this? Air conditioner size is measured in BTUs (British Thermal Units). Undersized units run constantly and can't cool your space. Oversized units short-cycle, waste energy, and fail to dehumidify properly. This calculator finds the right BTU rating for your room.
The rule of thumb: 20 BTU per square foot of living space. But ceiling height, sun exposure, and room occupancy all push that number up or down.
Who it's for: Homeowners buying a new AC window unit or sizing a central air system.
Room Details
Recommended AC Size
BTUs Required
—
minimum cooling capacity
Recommended
—
with 10% safety margin
Room Tonnage
—
for central AC systems
Energy Star Range
—
models to consider
Est. Annual Cost
—
at $0.12/kWh
Room Type
—
typical use case
Estimates only. Consult an HVAC contractor for central air sizing. Actual BTU needs vary by insulation, windows, and appliance heat load.