How central AC size is estimated
Air conditioners are sized in tons – one ton of cooling removes 12,000 BTU of heat per hour. A whole-house system for a typical US home is between 1.5 and 5 tons. The quick estimate starts from floor area and a climate factor (about 20 – 35 BTU per square foot), then adjusts for ceiling height, insulation, windows and the number of occupants.
BTU/h ≈ sq ft × climate factor × (ceiling ÷ 8 ft) × insulation × sun + 400 per extra occupant
Typical sizes
| Home size | Moderate climate | Hot climate |
|---|
| 1,000 sq ft | 2 tons | 2.5 tons |
| 1,500 sq ft | 3 tons | 3.5 – 4 tons |
| 2,000 sq ft | 4 tons | 5 tons |
| 2,500 sq ft | 5 tons | 2 systems |
These are average-construction figures. A well-insulated new home may need 25 – 30 % less; an older house with single-pane windows may need more.
Why not just buy bigger?
An oversized air conditioner cools the air quickly and shuts off before it has run long enough to remove moisture. The house feels cold and clammy, temperatures swing, energy use rises and the compressor wears out from frequent starts. Undersized units run constantly on the hottest days and can't hold the setpoint. Correct sizing gives the best comfort and lowest bills.
Manual J, S and D
Professional HVAC design uses three ACCA standards: Manual J calculates the heating and cooling load room by room; Manual S selects equipment that matches the load at local design conditions; Manual D sizes the ductwork to deliver the right airflow to each room. Good contractors perform these calculations instead of copying the size of the old unit.
Choosing the equipment
- Single-stage: lowest price; runs at full capacity or off.
- Two-stage: runs at about 65 – 70 % most of the time – quieter, better dehumidification.
- Variable-speed (inverter): modulates continuously for the best comfort and efficiency.
- Heat pump vs AC: a heat pump also heats efficiently and costs a little more than a cooling-only AC.
- Matched system: the outdoor unit and indoor coil should be an AHRI-certified match.
Frequently asked questions
What size AC do I need for a 2,000 sq ft house?
Usually around 3.5 – 4 tons in a moderate climate and up to 5 tons in hot climates, depending on insulation and windows.
How many square feet does a ton of AC cool?
Roughly 400 – 600 sq ft per ton, depending on climate and construction.
Is a bigger air conditioner better?
No. Oversized units short-cycle, remove less humidity and wear out faster.
What is a Manual J load calculation?
A room-by-room calculation of heat gain and loss from the ACCA standard, used to size heating and cooling equipment correctly.
How much airflow does a central AC need?
About 350 – 400 CFM per ton of cooling.
About TonRight
TonRight is an independent, free estimator for sizing central air conditioners and heat pumps. It uses rule-of-thumb load factors; a room-by-room ACCA Manual J calculation by a qualified contractor is the standard for final sizing. We are not an HVAC contractor or manufacturer.
Every formula on this page runs entirely in your web browser. The numbers you type are never uploaded, stored or shared. Our goal is simple: give you an honest starting point so you can compare product specifications with confidence and avoid paying for capacity you do not need – or buying something too small to do the job.
The methodology combines widely published engineering rules of thumb, manufacturer data sheets and the electrical code practices that installers use every day. We review the assumptions regularly and update the calculator when typical product specifications change.
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Last updated: October 28, 2026
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