How much electricity does an air conditioner use?

BTU/h and watts answer different questions

Cooling capacity is the rate of heat removal. Electrical input is the power drawn from the circuit. Two units with the same BTU/h can have different input power and efficiency.

Start with the nameplate or EnergyGuide

Use the rated watts, amps and volts, or an annual kWh figure when supplied. If you only have amps and volts, watts are approximately volts multiplied by amps; real equipment can vary while starting or cycling.

Runtime is the biggest swing factor

A unit that runs 30% of the hour uses far less than one that runs continuously. Track a hot day and a mild day separately, and do not turn a short heat wave into a full-season promise.

Planning boundary: the cooling estimator is a screening tool. Insulation, leakage, sunlight, connected rooms, maintenance, and climate can change the load and the actual bill.

A worked monthly example

A window unit drawing 900 watts while its compressor runs, averaging 8 hours of compressor time a day through a 30-day month.

900 W ÷ 1,000 = 0.9 kW, and 0.9 kW × 8 hours = 7.2 kWh a day, or 216 kWh for the month. At an illustrative $0.16 per kWh that is $34.56.

Eight hours means compressor time, not how long the unit is switched on. A unit left on for 12 hours that cycles its compressor two-thirds of the time uses the same eight hours of full power.

What an efficiency rating is worth

Room air conditioners are rated by Combined Energy Efficiency Ratio (CEER). A higher CEER means more cooling for each watt drawn.

The Department of Energy’s purchasing guidance for federal buyers compares three units of the same type. The least efficient, at a CEER of 10.9, is estimated at 826 kWh a year; an ENERGY STAR model at 14.7 uses 612 kWh; the best available at 15.4 uses 584 kWh. Under DOE’s stated assumptions that is $91, $67, and $64 a year.

Those figures come from a standardized use pattern. Your own savings scale with your own runtime and rate, so a unit that runs only a few weeks a year recovers a higher purchase price far more slowly than one that runs all summer.