Air Conditioner Size (BTU) & Heating Calculator
Find the right air conditioner size in BTU for a room using the ENERGY STAR chart, with adjustments for sun, occupants and kitchens — plus a heating BTU estimate by climate.
How to use
- 1Enter the room size in square feet (or metres).
- 2Adjust for shade or sun, the number of people and whether it's a kitchen; choose your climate for heating.
How it's calculated
Cooling: ENERGY STAR room-size chart; −10% if heavily shaded, +10% if very sunny, +600 BTU per person beyond two, +4,000 BTU for kitchens. Heating: area × BTU per sq ft by climate (≈ 30 in hot to 60 in cold climates).
Frequently asked questions
Why not just buy a bigger AC?
An oversized unit cools quickly but switches off before removing humidity, leaving the room cold and clammy and wasting energy.
How do BTU and tons relate?
One ton of cooling = 12,000 BTU per hour.
Is this a replacement for a Manual J calculation?
No — whole-house HVAC systems should be sized by a professional with a Manual J load calculation.