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Home & Garden — HVAC
BTU Calculator
Enter your room size, sun exposure and occupants to size an air conditioner in BTU per hour.
Cooling needed
—
BTU/hr for air conditioning.
| Room area | — |
|---|---|
| Base (20 BTU/ft²) | — |
| Sun adjustment | — |
| Extra occupants | — |
Show our math
Enter your figures above to see the step-by-step working.
Estimate — a load calculation is more preciseEverything computed client-side — nothing leaves this page
How the BTU Calculator Works
A BTU (British Thermal Unit) measures cooling and heating capacity. To size an air conditioner for a room, the rule of thumb is about 20 BTU per hour for every square foot of floor space. This calculator multiplies your room’s area by 20, then adjusts for how much sun the room gets and how many people use it regularly.
A very sunny room needs about 10% more capacity, a heavily shaded one about 10% less, and each person beyond two adds roughly 600 BTU. The result is the cooling load in BTU per hour; dividing by 12,000 gives it in “tons,” the unit used for larger units.
BTU/hr ≈ area × 20 × sun factor + extra occupants
Frequently Asked Questions
How many BTU do I need per square foot?
About 20 BTU per hour per square foot is the standard estimate for cooling. A 180 ft² room needs roughly 3,600 BTU/hr before adjustments for sun and occupancy.
What is a "ton" of air conditioning?
One ton equals 12,000 BTU per hour. So a 3,600 BTU/hr room needs about a third of a ton; window units are usually rated in BTU, central systems in tons.
What raises the BTU requirement?
Strong sun exposure, high ceilings, lots of occupants, kitchens and rooms with many windows all increase the load. This calculator adjusts for sun and extra people; add capacity for kitchens or very sunny glass-heavy rooms.
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