BTU Calculator
Find the right air conditioner size. A 300 sq ft room needs about 6,000 BTU per hour of cooling.
The BTU sizing rule
A common guide is 20 BTU per square foot for a room with 8 ft ceilings. Adjust upward for tall ceilings, sun, kitchens and extra occupants, and downward for shade.
Formula: area x 20 x (ceiling height / 8) x sunlight factor + 600 BTU per person beyond two + 4,000 for a kitchen. For 300 sq ft that is 6,000 BTU, or 0.5 tons.
Do not oversize
An air conditioner that is too big cools quickly and shuts off before it removes humidity, leaving the room clammy. One that is too small runs nonstop. Choose a unit close to the calculated BTU. This is for cooling a single room. For whole-house systems use the HVAC sizing calculator.
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Frequently asked questions
How many BTU do I need for 300 square feet?
About 6,000 BTU for a normal room with 8 ft ceilings.
How many square feet does a 12,000 BTU AC cool?
About 550 to 600 square feet.
What is a ton of AC?
One ton equals 12,000 BTU per hour.
Does the same calculation apply to heating?
No, heating needs depend on climate and insulation and are usually larger. Use the HVAC sizing calculator.
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