AC size for a 300 sq ft room
6,000 BTU
for a 300 sq ft room (0.5 tons) · about 500 W at EER 12
Adjust for the room
| Condition | BTU/h |
|---|---|
| Normal room | 6,000 |
| Very sunny (+10%) | 6,600 |
| Shaded (−10%) | 5,400 |
| Kitchen (+4,000) | 10,000 |
| Each extra person over 2 (+600) | +600 |
Rule of thumb: 20 BTU per sq ft with 8 ft ceilings (ENERGY STAR sizing guidance).
Monthly running cost at $0.17/kWh
| Use | Energy | Cost |
|---|---|---|
| 4 h/day | 60 kWh | $10 |
| 8 h/day | 120 kWh | $20 |
| 12 h/day | 180 kWh | $31 |
FAQ
What size AC for 300 square feet?
About 6,000 BTU (0.5 tons); add 10% for a sunny room and 4,000 BTU for a kitchen.
How much does it cost to run a 6,000 BTU AC?
At roughly 500 W, 8 hours a day for a month uses 120 kWh, about $20 at $0.17/kWh.