Find out exactly what size air conditioner your home needs. More accurate than simple square footage rules.
Answer these questions to get a personalized BTU recommendation.
Most online calculators use a simple formula: multiply your square footage by 20-25 BTU. That gives you a ballpark, but it can lead to an oversized or undersized unit — both of which cost you money.
Our calculator goes deeper. We use a modified version of the Manual J load calculation method, factoring in seven variables that significantly impact your cooling needs.
Base BTU = Square Footage × Climate Factor
+ Ceiling Height Adjustment
+ Insulation Adjustment
+ Sun Exposure Adjustment
+ Occupant Adjustment
= Total Recommended BTU
Hot climates (AZ, TX, FL) need 30-35 BTU/sq ft. Cool climates (MN, WI) need only 20-22 BTU/sq ft. This is the single biggest factor.
Standard 8ft ceilings are the baseline. Every foot above 8ft increases the air volume you need to cool by ~12.5%.
Good insulation (new homes, recent upgrades) can reduce your BTU need by 10-15%. Poor insulation increases it by 15-20%.
Heavily shaded homes need ~10% less cooling capacity. Homes with full sun exposure on most windows need ~10% more.
Each person generates about 600 BTU of heat. A household of 5+ adds meaningful cooling load beyond the standard calculation.
Your chosen SEER2 rating doesn't change your BTU need, but higher efficiency units maximize cooling performance at your calculated BTU.
An oversized AC cools quickly but cycles on and off rapidly (called "short cycling"), which wastes energy, wears out the compressor faster, and fails to properly dehumidify your home. An undersized unit runs constantly, struggles to reach your set temperature, and drives up your electricity bill.
The right size hits the sweet spot: efficient operation, proper humidity control, consistent comfort, and a longer equipment lifespan.
This calculator provides an excellent starting estimate. However, for homes with unusual layouts, large ductwork systems, or significant sun exposure variations between rooms, we recommend getting a full Manual J load calculation from a licensed HVAC contractor. This involves a room-by-room analysis that accounts for window orientation, wall construction, ductwork losses, and local design temperatures.
A professional Manual J calculation typically costs $100-300 and is well worth the investment for a system that may cost $5,000-15,000 installed.