How much electricity does an AC use per day?

A typical 8,000 BTU window unit run 8 hours a day uses about 6 kWh, roughly $0.96 at $0.16/kWh. Central air run through a hot day can use 25-40 kWh, costing $4-$6.50 a day at the US average rate.

Does an inverter AC really save money?

Yes, typically 20-40% less electricity than a fixed-speed unit of the same capacity, because it avoids repeated full-power compressor restarts. On a $46 monthly cooling bill that can mean $10-$18 saved per month in peak season.

Is it cheaper to leave the AC on all day or turn it off and on?

For most homes, letting the temperature drift up a few degrees while you are out and cooling down again when you return uses less total energy than holding one constant low temperature all day, especially with a fixed-speed unit.

How many watts does a 12,000 BTU air conditioner use?

Most 12,000 BTU (1-ton) units draw about 1,100-1,300 watts. At $0.16/kWh that is roughly $0.19 per hour of continuous running, or about $46 a month at 8 hours a day.

Does a bigger AC unit cost more to run?

A higher-BTU unit draws more watts, but an undersized unit for the space runs almost continuously, which can cost more overall than a correctly sized larger unit that cycles off once the room reaches temperature.

Cooling

How Much Electricity Does an Air Conditioner Use? (Cost Per Hour, Day and Month)

A small window AC (5,000-8,000 BTU) draws 450-800W and costs roughly $0.07-$0.13 per hour at the US average rate of $0.16/kWh, or about $17-$31 a month running 8 hours a day. A mid-size 12,000 BTU unit draws about 1,200W, costing around $0.19 per hour and $46 a month; in the UK the same unit costs roughly 31p per hour and £75 a month at 26p/kWh.

Air conditioning turns a modest summer electric bill into the biggest line item on the statement almost overnight, and the reason is simple: a compressor is one of the most power-hungry motors in an ordinary home. How much it actually costs depends on the unit's size in BTUs, whether it runs at a fixed speed or with an inverter compressor, and how many hours a day the thermostat calls for cooling. This guide breaks the cost down by wattage, by hour, day and month, and shows where an inverter model earns back its higher price tag.

BTU size and wattage: what you are actually paying for

Air conditioners are rated in BTU (British Thermal Units) of cooling capacity, but the number that determines your bill is the electrical wattage the compressor draws to deliver that cooling. A small 5,000 BTU window unit typically pulls 450-550W, an 8,000 BTU unit around 700-800W, a 12,000 BTU unit near 1,100-1,300W, and an 18,000 BTU unit can draw 1,700-2,000W. Central systems sized in tons rather than BTU (1 ton equals 12,000 BTU) run considerably higher, with a 3-ton central AC drawing 3,000-4,000W including the indoor blower. Bigger is not automatically worse per BTU delivered, but an oversized unit for the room wastes energy cycling on and off rapidly, so matching capacity to room size matters as much as the wattage label.

Cost per hour, day and month by unit size

Once you know the wattage, the arithmetic is the same for every appliance: divide watts by 1,000 for kilowatts, multiply by hours run, then multiply by your electricity rate. An 8,000 BTU window unit running 8 hours a day at the US average of $0.16/kWh costs about 700W × 8h × $0.16 = $0.90 a day, or roughly $27 a month. Run the same unit 24 hours a day through a heat wave and the monthly cost jumps past $80. Central air, drawing 3,500W and cycling roughly 40-50% of the time on a hot day, typically adds $150-$250 a month to a US summer bill. You can enter your own rate and unit wattage into the calculator on the home page to get a number matched to your actual bill rather than a national average.

5,000 BTU window unit (~500W): about $0.08/hour, $19/month at 8 h/day
8,000 BTU window unit (~750W): about $0.12/hour, $29/month
12,000 BTU unit (~1,200W): about $0.19/hour, $46/month
18,000 BTU unit (~1,850W): about $0.30/hour, $71/month
3-ton central AC (~3,500W, 45% duty cycle): about $150-$250/month in peak summer

Inverter vs fixed-speed compressors

A fixed-speed (non-inverter) air conditioner runs its compressor at full power until the room hits the target temperature, then switches off completely, and repeats that cycle all day. An inverter unit instead varies compressor speed continuously, ramping down to a fraction of full power once the room is close to temperature rather than switching off and restarting. Because restarting a compressor is one of the most electrically demanding moments in its cycle, inverter units typically use 20-40% less electricity than a fixed-speed unit of the same cooling capacity over a full day, and they hold room temperature far more steadily. The trade-off is upfront price: inverter window and split units usually cost 25-50% more to buy, so the payback period is generally two to four cooling seasons in a hot climate and longer in a mild one.

SEER and EER ratings: comparing efficiency properly

US central and split systems carry a SEER (Seasonal Energy Efficiency Ratio) rating, and window units carry an EER (Energy Efficiency Ratio); both describe cooling output divided by electricity input, so a higher number means less electricity for the same cooling. Federal minimums have risen to SEER 14-15 in most US states, but older systems installed a decade or more ago may sit at SEER 10-13, using roughly 20-30% more electricity than a new minimum-efficiency system for identical cooling. Upgrading a genuinely old central AC to a modern SEER 16-18 unit commonly cuts the cooling portion of a summer bill by a fifth to a third, though the upfront cost of replacement is substantial and should be weighed against remaining equipment life.

Practical ways to lower AC running costs

Set the thermostat to 78°F (25-26°C) rather than 72°F; each degree lower adds roughly 3-5% to cooling energy use
Use a programmable or smart thermostat to let the house warm slightly while nobody is home
Close blinds and curtains on sun-facing windows during the hottest hours to cut heat gain before it reaches the AC
Replace or clean the air filter monthly in cooling season; a clogged filter forces the compressor to work harder for the same cooling
Size any replacement unit correctly for the room or house; an oversized unit cycles inefficiently and cools unevenly

Air conditioner running cost by size and electricity rate (8 hours/day, 30 days)

Unit	Watts	Per hour @ $0.16	Per month (US)	Per month @ 26p (UK)
5,000 BTU window unit	500W	$0.08	$19	£31
8,000 BTU window unit	750W	$0.12	$29	£47
12,000 BTU unit	1,200W	$0.19	$46	£75
18,000 BTU unit	1,850W	$0.30	$71	£115
3-ton central AC (45% duty)	~1,575W avg	$0.25	$180*	£293*

Frequently asked questions

How much electricity does an AC use per day?: A typical 8,000 BTU window unit run 8 hours a day uses about 6 kWh, roughly $0.96 at $0.16/kWh. Central air run through a hot day can use 25-40 kWh, costing $4-$6.50 a day at the US average rate.
Does an inverter AC really save money?: Yes, typically 20-40% less electricity than a fixed-speed unit of the same capacity, because it avoids repeated full-power compressor restarts. On a $46 monthly cooling bill that can mean $10-$18 saved per month in peak season.
Is it cheaper to leave the AC on all day or turn it off and on?: For most homes, letting the temperature drift up a few degrees while you are out and cooling down again when you return uses less total energy than holding one constant low temperature all day, especially with a fixed-speed unit.
How many watts does a 12,000 BTU air conditioner use?: Most 12,000 BTU (1-ton) units draw about 1,100-1,300 watts. At $0.16/kWh that is roughly $0.19 per hour of continuous running, or about $46 a month at 8 hours a day.
Does a bigger AC unit cost more to run?: A higher-BTU unit draws more watts, but an undersized unit for the space runs almost continuously, which can cost more overall than a correctly sized larger unit that cycles off once the room reaches temperature.

Key takeaways

Wattage, not BTU alone, determines your electricity cost; check the unit's watt rating on the nameplate
A window unit typically costs $0.08-$0.30 per hour depending on size; central AC costs $150-$250 a month in peak summer
Inverter compressors use 20-40% less electricity than fixed-speed units of the same capacity
Every degree above 72°F on the thermostat saves roughly 3-5% on cooling costs
Enter your unit's wattage and local rate into the calculator on the home page for an exact monthly figure

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