BTU Calculator
Free BTU calculator for AC sizing — cooling power and AC tonnage for a room from area, sun exposure, and occupants.
Everyday Uses
AC sizing
Match a window or portable AC to the room it needs to cool.
Sun & people
Adjust for sunny rooms, extra occupants, and kitchens.
Efficiency
Avoid an oversized unit that short-cycles and wastes energy.
Any room
From a small office to an open-plan living room.
Frequently Asked Questions
How many BTUs do I need to cool a room?
A common rule of thumb is about 20 BTU per hour for each square foot of floor area. A 250 ft² room needs roughly 5,000 BTU/hr. Add about 10% for a very sunny room (subtract 10% for a shaded one), add 600 BTU for each person beyond two, and add 4,000 BTU for a kitchen. This calculator applies all of those adjustments.
How many tons of AC is that?
One "ton" of air conditioning equals 12,000 BTU per hour. So a 6,000 BTU room needs about a half-ton unit, and a 24,000 BTU load needs a 2-ton system. Tonnage refers to cooling capacity, not the unit's weight.
Is bigger always better for an AC unit?
No. An oversized AC cools the air quickly but short-cycles before it removes humidity, leaving the room cold and clammy and wearing out the compressor. Matching the unit to the calculated load gives steadier temperatures, better dehumidification, and lower running costs.