Start with the right kind of watts
A label that says 800 watts does not mean an air conditioner consumes 800 watts every moment it is switched on. Its compressor may stop and restart, or vary its speed. For a useful cost estimate, use average power over the period you want to model.
If a compatible energy monitor reports 4.8 kWh across eight hours, average power for that period was 4.8 ÷ 8 × 1,000 = 600 watts. Check the monitor’s electrical rating and the appliance instructions before using one. Built-in consumption reporting can also be useful; record what period the reading covers.
Work through one example
Suppose average power is 600 watts, daily use is eight hours, and the appliance operates on 30 days. At an illustrative rate of $0.18 per kWh:
- 600 ÷ 1,000 = 0.6 kW.
- 0.6 × 8 = 4.8 kWh per day.
- 4.8 × 30 = 144 kWh per month.
- 144 × $0.18 = $25.92 per month.
Four identical months would cost $103.68. That is a scenario, not a measured national average or a promise about any model.
Check how sensitive the answer is
| Illustrative average draw | Monthly kWh | Monthly cost |
|---|---|---|
| 400 W | 96 | $17.28 |
| 600 W | 144 | $25.92 |
| 800 W | 192 | $34.56 |
All three rows use eight hours per day, 30 days and $0.18/kWh. Keeping the other inputs fixed helps you see which assumption matters. It does not establish that a particular appliance will average any of these values.
Use your rate, not your whole bill
Find the usage-based price on your electricity bill. Include relevant per-kWh supply and delivery charges; leave fixed account fees out when estimating the extra cost of this appliance. If your tariff changes by time of day, calculate each time band separately.
Measure again during different weather before treating one day as representative of the entire summer. Save the dates and conditions alongside your reading, then update your planning estimate.
Compare tariffs, then make the example yours
At an average 600 W, one hour uses 0.6 kWh. At $0.18/kWh that hour costs $0.108, or about 11 cents. Changing the tariff changes the cost without changing energy use.
| Rate | Cost per hour | Cost over 30 days |
|---|---|---|
| $0.12/kWh | $0.072 | $17.28 |
| $0.18/kWh | $0.108 | $25.92 |
| $0.30/kWh | $0.180 | $43.20 |
These rates are illustrative, not current national or state averages. The same 144 kWh is used in every row. Open this AC example in the calculator, then change the tariff or schedule. For consumption that changes across the summer, use a separate row for each month.
Window AC cost planner
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Sources & further reading
Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.