How much electricity does an air conditioner use?
It depends on the electrical power, not on the BTU rating.
A domestic 12,000 BTU/h unit of average efficiency draws roughly 1,000-1,300 W, a little over 1 kWh for every hour of continuous running. The BTU rating says nothing about consumption.
Typical consumption by unit size
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| Unit | Power input | kWh per hour | kWh per month (8 h/day) |
|---|---|---|---|
| 6,000 BTU (0.5 ton) | 500-700 W | 0.5-0.7 | 120-168 |
| 9,000 BTU (0.75 ton) | 750-1,000 W | 0.75-1.0 | 180-240 |
| 12,000 BTU (1 ton) | 1,000-1,300 W | 1.0-1.3 | 240-312 |
| 18,000 BTU (1.5 ton) | 1,500-2,000 W | 1.5-2.0 | 360-480 |
| 24,000 BTU (2 ton) | 2,000-2,700 W | 2.0-2.7 | 480-648 |
The BTU confusion
A 12,000 BTU/h unit does not consume 12,000 W. BTU/h measures the heat it pulls out of the room; the watts on your bill are the electricity going in. The relationship between them is precisely the efficiency rating.
In fact an air conditioner moves more thermal energy than it consumes in electricity: it does not create cold, it relocates heat outside. That is why a unit with an EER of 3 delivers three times as much cooling as the electricity it uses.
How to find your unit's consumption
- Check the rating plate on the outdoor unit: look for "power input" or "rated consumption", in W or kW.
- If it is not listed, use the capacity and the EER: power = capacity / EER.
- Multiply by hours of use to get kWh.
Why real consumption is usually lower
The table assumes continuous running at rated power, which is the worst case. In practice:
- An inverter unit drops to part load once the room is at temperature, drawing a fraction of its rating.
- The unit only works flat out during the hottest hours.
- A well-insulated home holds temperature with less input.
It is reasonable to expect real consumption between 50 and 70 % of the continuous-running figure, if the unit is correctly sized.
Sources and methodology
Conversions use exact constants: 1 BTU/h = 0.29307107 W and 1 frigorie/h = 1 kcal/h = 1.163 W. The component sizing model (load per volume by insulation level, 120 W per person, solar gain by glazed area) is set out in full on the air conditioner size calculator. It is a guideline estimate: a professional heat-load calculation considers considerably more variables.
Frequently asked questions
How much power does a 12,000 BTU air conditioner use?
Roughly 1,000 to 1,300 W depending on efficiency, so a little over 1 kWh per hour of continuous running.
Does a 12,000 BTU unit use 12,000 watts?
No. BTU/h measures cooling capacity, not consumption. That unit draws around 1,000-1,300 W.
How many kWh per month does an AC use?
At 1,000 W for 8 hours a day over 30 days, about 240 kWh. With a well-sized inverter, considerably less.
How do I calculate consumption from the EER?
Divide the capacity by the EER: 12,000 BTU/h with an EER of 10 gives 1,200 W.
Does it use more when starting up?
Yes, start-ups have a consumption spike. That is why switching on and off constantly costs more than holding a steady temperature.