Air Conditioner Size Calculator
BTU capacity for a room.
Reviewed by James Whitfield · How we check our maths
Your values
ⓘ Live results
Results
- Required capacity
- 6,000 BTU/h
- In tons
- 0.5
- Typical unit to buy
- 1 ton
- Estimated running watts
- 600
- Room area
- 300 sq ft
Quick answer
Start from 20 BTU per square foot, then adjust for sunlight, ceiling height, kitchens and extra occupants.
The formula
BTU = area × 20 + adjustments
Worked example
Worked example
Using the values the calculator loads with.
Inputs
- Room area300 sq ft
- Ceiling height8 ft
- Regular occupants2
- Sun exposureAverage
- Is it a kitchen?No
Result
- Required capacity6,000 BTU/h
- In tons0.5
- Typical unit to buy1 ton
- Estimated running watts600
- Room area300 sq ft
How to use the Air Conditioner Size Calculator
- 1Measure the room's floor area in square feet.
- 2Enter ceiling height and occupancy.
- 3Adjust for sun exposure and kitchen heat.
Frequently asked questions
Is bigger better?
No — an oversized unit short cycles and leaves the room humid.
What about insulation?
Poorly insulated rooms need 10–20% more capacity.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error