AC size for a 450 sq ft room
9,000 BTU
for a 450 sq ft room (0.8 tons) · about 750 W at EER 12
Adjust for the room
| Condition | BTU/h |
|---|---|
| Normal room | 9,000 |
| Very sunny (+10%) | 9,900 |
| Shaded (−10%) | 8,100 |
| Kitchen (+4,000) | 13,000 |
| 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 | 90 kWh | $15 |
| 8 h/day | 180 kWh | $31 |
| 12 h/day | 270 kWh | $46 |
FAQ
What size AC for 450 square feet?
About 9,000 BTU (0.8 tons); add 10% for a sunny room and 4,000 BTU for a kitchen.
How much does it cost to run a 9,000 BTU AC?
At roughly 750 W, 8 hours a day for a month uses 180 kWh, about $31 at $0.17/kWh.