BTU / AC Sizing Calculator

Free tool — embed on your site for free.

Room / area square footage sq ft

Climate zone

Home construction quality

Regular occupants

Is this a kitchen? Yes

Heavily shaded (covered porch, north-facing, mature trees)? Yes

Sun-exposed (south/west-facing, lots of windows)? Yes

You need

BTU capacity needed

12,500 BTU/hr

500 sq ft × 25 BTU/sq ft × 1 construction factor + occupancy and solar adjustments
Equivalent tons

1.04 tons

1 ton of cooling = 12,000 BTU/hr
Recommended AC unit size

15,000 BTU

Closest standard unit ≥ calculated BTU needs. Oversizing causes short-cycling — avoid going bigger.

This is a rule-of-thumb estimate good to ±20%. For a new whole-house system, have an HVAC contractor run a Manual J load calculation — it accounts for window orientation, duct losses, and infiltration rates that this simple formula does not.