WattBasis | Understand what your home costs to run

A window air conditioner drawing 800 watts for six effective cooling hours per day would cost $28.80 over 30 days at $0.20 per kilowatt-hour. That is an illustrative calculation, not a national average or a prediction for your particular model.

Your estimate depends on the electricity the unit uses, how long it draws that power, and your electricity rate.

How to calculate your running cost

Use this formula:

Monthly cost = (watts ÷ 1,000) × effective hours per day × days × electricity rate in dollars per kWh.

Watts describe power; kilowatt-hours measure energy used over time. Dividing watts by 1,000 converts them to kilowatts. See the U.S. Energy Information Administration's explanation of electricity measurements:

https://www.eia.gov/energyexplained/electricity/measuring-electricity.php

For our example:

800 watts ÷ 1,000 = 0.8 kilowatts.

0.8 × 6 hours = 4.8 kWh per day.

4.8 × $0.20 = $0.96 per day.

$0.96 × 30 days = $28.80 per month.

Find the correct inputs

Look for electrical input power in watts on your model's label or specifications. Cooling capacity, often listed in BTU/h, is not the electrical wattage to enter in the calculator.

Use the variable electricity charges applicable to your account. For 20 cents per kWh, enter 0.20, not 20. This simple estimate excludes fixed charges and separately billed taxes. If your rate changes by time of day, calculate each period separately and add the results.

Why hours switched on can be misleading

Conventional air conditioners cycle their compressors on and off. Variable-speed models can adjust compressor output instead. ENERGY STAR explains these differences in its room air conditioner guidance:

https://www.energystar.gov/products/room_air_conditioners

For a simplified example, a unit switched on for eight hours with its compressor operating half that time has four compressor-running hours. That 50% assumption is only an example; do not assume it applies to your room.

Our calculator uses constant power during the hours you enter. It does not separately model fan-only operation or standby consumption. Using rated cooling power for every hour switched on can overestimate usage; counting only compressor hours can omit other consumption. Measured energy use gives a better basis when available.

Compare three usage scenarios

Using the same assumed 800-watt input, $0.20/kWh rate, and 30-day month:

• Four effective hours per day: 96 kWh and $19.20.

• Six effective hours per day: 144 kWh and $28.80.

• Eight effective hours per day: 192 kWh and $38.40.

These are calculated scenarios, not product test results. They show how changing one input affects the estimate.

Does a larger air conditioner always make sense?

Choose capacity for the space you need to cool. ENERGY STAR notes that oversized units may cool a room before removing enough humidity. Its guidance also recommends following installation instructions and sealing around the unit to reduce air leaks. See its room air conditioner buying guidance above.

Would replacing your unit pay for itself?

Suppose a replacement costs $150 more than an alternative and saves 40 kWh per cooling month under comparable conditions. At $0.20/kWh, that saves $8 per month. Recovering the extra $150 would take about 19 cooling months, or nearly five years if used four months each year.

Those figures are hypothetical. Compare documented consumption, purchase prices, and your usage before making a decision.

Try your own numbers

Open Calculators in the menu and enter your wattage, effective daily hours, electricity rate, and days. Compare a lighter-use scenario with a heavier-use scenario to see a range based on your assumptions.

This guide provides energy-cost estimates. It does not report hands-on product testing or guarantee savings.