What size air conditioner do I need for my house?

Square-foot charts size every house as if it sat in the same summer. Enter your city and get the size for its real design day, from 30 years of NOAA weather, plus what it costs to run there.

Your city

3,206 US cities, each sized from its nearest NOAA weather station.

A sq ft house. The chart says **3.5 tons** everywhere.
City	Design day	Size it needs
Phoenix, AZ	112°F	5 tons	chart is short
Houston, TX	101°F	4 tons	chart is close
Atlanta, GA	96°F	3.5 tons	chart is close
Denver, CO	96°F	3 tons	chart is 29% over
Chicago, IL	90°F	2.5 tons	chart is 41% over
Seattle, WA	82°F	2 tons	chart is 93% over

Why bigger is not safer

Of 3,206 cities here, the square-foot chart oversizes 2,150 and undersizes 171. Oversizing is the common mistake and the one people do not notice. A unit that is too big hits the thermostat in a few minutes and shuts off before the coil has pulled water out of the air, so the room reads 72°F and feels damp. It also starts and stops more, which wears the compressor.

Industry sizing (ACCA Manual S) allows a central unit up to 15% over the calculated load. The sizes here assume average insulation and sun; your city's page lets you change both. A contractor's room-by-room Manual J is still the final word on a whole-house system.

Every city, by state