How Much Electricity Does an Air Conditioner Use?
A typical central air conditioner uses 3,000–3,500 watts while running; a window unit 500–1,500 W; a mini-split 500–1,000 W. In dollars, running a mid-size central AC costs roughly $0.50 an hour at $0.15/kWh — which is why cooling is the single biggest driver of a summer electricity bill in hot climates.
Power use by AC type
| AC type | Cooling capacity | Running watts | Cost/hour* | Cost/month† |
|---|---|---|---|---|
| Small window unit | 5,000–8,000 BTU | 450–750 W | $0.07–0.11 | $16–27 |
| Large window unit | 12,000–14,000 BTU | 1,100–1,500 W | $0.17–0.23 | $40–54 |
| Portable AC | 8,000–14,000 BTU | 900–1,400 W | $0.14–0.21 | $32–50 |
| Mini-split (single zone) | 9,000–12,000 BTU | 500–1,000 W | $0.08–0.15 | $18–36 |
| Central AC (2.5 ton) | 30,000 BTU | 3,000–3,500 W | $0.45–0.53 | $108–126 |
| Central AC (4 ton) | 48,000 BTU | 4,800–5,500 W | $0.72–0.83 | $173–198 |
*at $0.15/kWh, running continuously. †assuming 8 hours a day for 30 days. Real bills are lower than "continuous" because the compressor cycles off once the room hits temperature — see duty cycle below.
The number that really decides your bill: duty cycle
An AC's nameplate watts tell you its draw while the compressor runs — but it doesn't run constantly. On a mild day it might run 30% of the time; in a heatwave, 70–80%. That fraction is the duty cycle, and it's the difference between a $60 and a $150 cooling month for the same unit. Two things lower it more than anything else: a higher thermostat setpoint (every degree warmer cuts run time), and a well-sealed, shaded, insulated room.
How to calculate your own AC cost
The formula is watts ÷ 1,000 × hours run per day × rate. A 1,200 W window unit running an effective 6 hours a day at $0.18/kWh costs 1,200 ÷ 1,000 × 6 × 0.18 = $1.30 a day, about $39 a month. Our AC running cost calculator does this with duty cycle built in, and takes BTU as well as watts.
Five ways to cut AC running cost
- Raise the setpoint. 78°F/26°C instead of 72°F/22°C can cut cooling cost 15–30% — the compressor simply runs less.
- Right-size the unit. An oversized AC short-cycles: it cools fast, shuts off before removing humidity, then restarts — wasteful and clammy. Size it with the BTU calculator.
- Seal and shade. Blocking afternoon sun and sealing gaps around the unit cuts the heat it has to fight.
- Use fans. A ceiling fan (30–75 W) lets you raise the thermostat a few degrees at a fraction of the cost.
- Consider a heat pump / inverter mini-split. Variable-speed units modulate instead of cycling on-off, often using 30–50% less energy than old central systems — and they heat too. Compare in the heat pump savings calculator.
FAQ
How much does it cost to run AC for 24 hours?
A mid-size central AC (3,300 W) at a 60% duty cycle uses about 47 kWh a day — roughly $7 at $0.15/kWh. A window unit (1,000 W) at the same duty cycle is about $2.20 a day.
Does a bigger AC use more electricity?
Per hour, yes — but a correctly sized unit that runs steadily can use less overall than an undersized one running flat out or an oversized one short-cycling. Match capacity to the room.
Is a mini-split cheaper to run than window units?
Usually. Inverter-driven mini-splits modulate their output and have high efficiency ratings (SEER 18–30), so they typically cool for less than older fixed-speed window or central units.
Related tools
- AC / Heater Running Cost — your exact cost by watts or BTU.
- BTU / AC Size — the right size for your room.
- Appliance Wattage Chart — where AC sits among your other loads.