AC Size Calculator
What size air conditioner do I need?
A quick estimate from the area you're cooling, adjusted for sun, people and a kitchen. For a whole-house system, a contractor's load calculation (Manual J) is the real answer.
- In tons
- 0.7 tons
Central AC is sold in tons: 1 ton = 12,000 BTU/hr.
An estimate to plan and budget with. Measure carefully and check the product’s own figures before you buy.
Results update as you type.
How it’s calculated
- 1
The starting point is about 20 BTU per square foot of space with 8 ft ceilings (the ENERGY STAR room AC guideline), scaled for taller ceilings.
- 2
We take off 10% for a heavily shaded space, add 10% for a very sunny one, add 600 BTU for each regular occupant past two, and 4,000 BTU for a kitchen.
Before you buy
Bigger isn't better: an oversized AC cycles on and off, wastes energy and leaves the air clammy.
Insulation, windows, climate and duct leaks change the answer a lot for a whole house.
For central air or a heat pump, ask for a Manual J load calculation rather than a rule of thumb.
Questions
How many BTUs do I need per square foot?
About 20 BTU per square foot is a common starting point for a room with 8 ft ceilings, adjusted for sun, occupants and heat from a kitchen.
What size AC do I need for 1,500 sq ft?
The rule of thumb gives about 30,000 BTU, or 2.5 tons, but whole homes vary widely with insulation and climate. An HVAC contractor's load calculation gives the right size.