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Air Conditioner BTU Calculator

Estimate the air conditioner size in BTU for a room from its square footage, sun exposure, occupants and kitchen use, plus the running cost.

Room area (ft²)

Sun exposure

People regularly in the room

Kitchen?

Efficiency (EER)

Hours per day

Electricity price ($/kWh)

How to use it

Enter the room area.
Adjust for sun and shade, people and kitchens.
EER is on the yellow EnergyGuide label (higher = more efficient).

How it works

Rule of thumb: about 20 BTU per ft², +10% for very sunny rooms, −10% for shaded, +600 BTU per person beyond two, +4,000 BTU for kitchens. Power draw ≈ BTU ÷ EER watts.

FAQ

What size AC for 400 square feet?

About 8,000-9,000 BTU for a typical room; more if very sunny or a kitchen.

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