What size AC unit do I need for 500 square feet?
Check it with your own numbers
Open the BTU Calculator with these values
| Room length | 25 ft |
| Room width | 20 ft |
| Sun exposure | Average |
| Regular occupants | 2 |
| Is it a kitchen? | No |
| Recommended capacity | 10,000 BTU |
| Room area | 500 ft² |
| Tons (cooling) | 0.83 |
The base number
At 20 BTU per square foot, 500 ft² × 20 = 10,000 BTU. In tons, that is 0.83. This assumes 8 ft ceilings, average sun, decent insulation and two people.
What a 500 sq ft space usually is
At this size you are usually cooling a studio apartment, a large living room, a finished basement or a garage converted to living space. Each has its own twist:
- Studio with a kitchen. Cooking adds heat. Set "Is it a kitchen?" to Yes and the calculator adds 4,000 BTU, pushing you to about 14,000.
- Finished basement. Below-grade rooms stay cool. You can often drop 10 to 20%.
- Converted garage. Often poorly insulated, with a big door. Size up and insulate first.
- Open plan. If the 500 ft² opens to a hallway or stairs, cool air will spill out. Measure the whole connected area.
Unit options around 10,000 BTU
Window unit
10,000 BTU window units still run on standard 115-volt power. Check that the outlet is on a 15 or 20 amp circuit without much else on it.
Through-the-wall
A good choice for a garage conversion where windows are small. Sleeve sizes vary by brand, so buy the sleeve and unit together.
Mini split
A 9,000 BTU mini split head is a common match. Variable-speed inverter compressors handle a slight undersize better than a window unit does, since they run longer at low speed and dehumidify well. A 12,000 BTU head covers you if the room is sunny or has a kitchen.
Central air note
If you are adding 500 ft² to a house with central air, do not assume the existing system can absorb it. A typical 3-ton system is sized for the original house; an addition often needs its own mini split.
Related questions
For other sizes, use the full BTU Calculator or browse all answers.