BTU Calculator
Cooling capacity a room needs, in BTU/hr, tons, and watts
Cooling Needed
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Frequently Asked Questions
How many BTUs do I need to cool a room?
A common rule is about 20 BTU per square foot. A 300 sq ft room needs roughly 6,000 BTU. This calculator refines that with ceiling height, number of occupants, kitchen heat, and sun exposure for a better match.
What happens if the AC is too big or too small?
Too small and it runs constantly without cooling well. Too big and it cools fast but short-cycles, leaving the room humid and clammy and wearing out the compressor. Right-sizing matters for comfort, humidity, and efficiency.
How do BTUs convert to tons and watts?
1 ton of cooling = 12,000 BTU/hr. To convert BTU/hr to watts, divide by 3.412. So a 12,000 BTU unit is 1 ton and about 3,517 watts of cooling.
Do kitchens and sunny rooms need more cooling?
Yes. Add about 4,000 BTU for a kitchen because of appliance heat, add roughly 10% for a very sunny room, and subtract about 10% for a heavily shaded one. Each extra person beyond two adds around 600 BTU.
Is BTU used for heating too?
Yes — furnaces and heat pumps are also rated in BTU/hr. Heating needs depend heavily on climate and insulation, so a cooling estimate is only a rough starting point for heating; a Manual J load calculation is best for sizing a furnace.