AC Size (BTU) Calculator
Enter the room's length and width. The calculator suggests the cooling capacity to look for, adjusted for sunlight, extra people and kitchens.
Type a number and the answer appears straight away.
Cooling capacity needed7,000 BTU per hour
- Room area
- 300 sq ft
- Base size for that area
- 7,000 BTU
- In tons of cooling
- 0.58
- In kilowatts
- 2.05
An approximate guide for rooms with 8-foot ceilings, based on ENERGY STAR sizing guidance. A unit that is too big cools quickly but leaves the air damp; for whole-house systems ask an HVAC contractor for a load calculation.
The math behind it: AC Size (BTU)
base BTU for the room's area, plus 10% if sunny or minus 10% if shaded, plus 600 per person beyond two, plus 4,000 for a kitchen
A 15 ft by 20 ft room is 300 square feet and needs about 7,000 BTU per hour. A small 12 ft by 12 ft bedroom needs about 5,000 BTU.
This is an approximate guide for rooms with 8 foot ceilings, based on ENERGY STAR sizing guidance. An oversized unit cools the room quickly but switches off before it has removed the humidity, leaving the air clammy.
Common questions
What size air conditioner do I need?
Work out the room's area in square feet. Up to 150 square feet needs about 5,000 BTU, 250 to 300 square feet about 7,000, and 450 to 550 square feet about 12,000.
How many BTU do I need per square foot?
Roughly 20 to 30 BTU per square foot for a single room, with smaller rooms at the higher end. Sunny rooms, kitchens and extra people need more.
How many BTU is one ton of cooling?
12,000 BTU per hour. A 24,000 BTU unit is a 2-ton air conditioner.
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