The cost of your AC unit depends on the size, the type, and the cost of electricity in your area. For example: A standard 3-ton AC will use 4.32 kilowatts per hour. If the cost of electricity in your area is $12.65 cents per kilowatt per hour, the cost of your AC is about 55 cents per hour. It doesn’t sound like much, but if you run your unit for 10 hours per day for 30 days, you’re looking at $165 per month.