AC BTU Calculator
Estimate the air conditioner cooling capacity (in BTU/hour) needed to efficiently cool a room.
How AC BTU works
Sizing an air conditioner correctly is vital for climate control. A unit that is too small cannot keep up, while one that is too large will cycle off too quickly, leaving the room damp.
This calculator uses standard US Department of Energy rules: 20 BTU of cooling power per square foot of room area, adjusted for thermal variables like occupant heat load, direct solar heating, and ovens.
Base BTU/hr = Room Area (sq ft) × 20Adjusted BTU = Base BTU ± Solar Offset (+10% Sunny / -10% Shaded) + Occupant Load (+600 BTU per person > 2) + Kitchen Offset (+4,000 BTU)1 ton of refrigeration = 12,000 BTU/hr.
AC BTU conversion table
| Room Area (sq ft)↕ | Required AC Capacity (BTU/hr)↕ | AC Class Sizing↕ |
|---|---|---|
| 100 to 150 sq ft | 5,000 BTU/hr | Small Bedroom / Office |
| 150 to 250 sq ft | 6,000 BTU/hr | Medium Bedroom / Den |
| 250 to 350 sq ft | 8,000 BTU/hr | Large Bedroom / Small Living Room |
| 350 to 450 sq ft | 10,000 BTU/hr | Large Living Room / Suite |
| 450 to 550 sq ft | 12,000 BTU/hr (1 Ton) | Open Plan Floor / Large Room |
| 550 to 700 sq ft | 14,000 BTU/hr | Large Studio / Small Apartment |
FAQ: AC BTU
How do you determine what size AC I need?
Calculate the square footage of the room (Length × Width). Multiply that by 20 to get the base BTU load. Add 600 BTUs per person if more than two people occupy the room, and add 4,000 BTUs if the room is a kitchen.
What happens if an AC is too big for a room?
It cools the room too fast, which sounds good but is highly inefficient. The unit will satisfy the thermostat before it has had time to remove humidity from the air, resulting in a clammy, cold, and humid room.