AC Sizing Calculator
Find the right AC size for your home based on square footage, climate, and other factors.
AC Sizing Calculator
Enter your home details for an AC size recommendation.
How AC Sizing Works
AC systems are measured in tons (1 ton = 12,000 BTU/hour of cooling capacity). Proper sizing ensures your home cools efficiently without wasting energy or creating comfort problems.
The Tonnage-per-Square-Foot Method
A common rule of thumb is 1 ton per 500–600 sq ft, adjusted for climate:
- Hot/humid climates (FL, TX, AZ, LA): 1 ton per 400–500 sq ft
- Moderate climates (NC, TN, KS, northern CA): 1 ton per 500–600 sq ft
- Cool climates (WA, OR, northern states): 1 ton per 600–700 sq ft
A 2,000 sq ft home in Phoenix might need a 4–5 ton unit, while the same home in Seattle might only need 3 tons.
Why Correct Sizing Matters
- Undersized: Runs constantly, can't keep up on the hottest days, high energy bills, shortened lifespan from overwork, poor humidity control.
- Oversized: Short-cycles (turns on/off rapidly), poor humidity removal (the biggest comfort complaint), uneven temperatures, higher energy bills, premature compressor failure.
- Right-sized: Runs in longer, efficient cycles that properly dehumidify, maintain even temperatures, and maximize equipment life.
Factors That Adjust Sizing
- Insulation quality: Well-insulated homes need 20–30% less cooling capacity
- Window area and orientation: South/west-facing windows with no shade add significant heat load
- Ceiling height: Increase by 10–15% for 9–10 foot ceilings
- Number of occupants: Each person adds ~400 BTU/hour of heat
- Kitchen and appliances: Homes with large kitchens or server rooms need more cooling
Professional Manual J Calculation
For the most accurate sizing, have an HVAC contractor perform a Manual J load calculation. This is the ACCA (Air Conditioning Contractors of America) standard that accounts for all variables. Many contractors will perform this for free as part of a replacement quote. Our calculator uses a simplified Manual J approach for quick estimates.
Frequently Asked Questions
What size AC do I need for my house?
A general rule is 1 ton (12,000 BTU) per 500–600 sq ft, adjusted for climate. A 2,000 sq ft home in a hot climate typically needs a 3.5–4 ton unit, while the same home in a mild climate needs 3–3.5 tons.
What happens if my AC is too small?
An undersized AC runs continuously, cannot cool the home on the hottest days, and leads to high energy bills and excessive wear. It may also struggle with humidity control.
What happens if my AC is too big?
An oversized AC cools too quickly and short-cycles, leading to poor humidity removal, uneven temperatures, higher energy bills, and premature compressor failure.
What is a Manual J calculation?
Manual J is the HVAC industry standard for calculating heating and cooling loads. It considers 8+ factors including square footage, insulation, windows, orientation, climate, and occupants. Our calculator uses a simplified version.
Does insulation affect AC sizing?
Significantly. A well-insulated home with good windows may need 25–30% less cooling capacity. Improving insulation before replacing your AC can mean buying a smaller, more efficient system.
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