The short answer
At a stated constant electrical input, AC hourly cost is input kW multiplied by your price per kWh. Multiply by actual use hours and chosen use days for a period estimate. BTU/h capacity is not electrical input, and thermostat cycling or a seasonal annual label requires an appropriately different basis.
Use electrical input for the hourly cost
Hourly electricity cost at a stated input = input kW × price per kWh.
An illustrative AC drawing 1,000 W continuously costs $0.20 for one hour at an illustrative $0.20/kWh. The 1,000 W must describe electricity input. A BTU/h capacity or a cooling-output kW figure is unsuitable for this field.
The AC calculator applies the same arithmetic to portable, window or other units when you provide a compatible input. It does not assign a universal wattage to each design.
Extend your own routine to a month or season
For a constant 1 kW input, five daily hours and 30 cooling use days:
| Step | Result |
|---|---|
| 1 kW × 5 hours | 5 kWh per use day |
| 5 kWh × 30 use days | 150 kWh |
| 150 kWh × $0.20/kWh | $30.00 |
| The same daily assumption across 90 use days | 450 kWh, costing $90.00 |
Those are illustrative scenarios, not typical monthly bills. Enter the number of days you actually intend to model; a month with 12 cooling days differs from a month with daily use.
Account for changing compressor operation
ENERGY STAR explains that room AC operation includes a compressor and fans, and that energy-saving control can alter fan operation when the compressor turns off.
Consequently, a maximum input rating multiplied by every enabled hour can be an unsuitable estimate of average energy. Variable operating conditions can also make a single watt snapshot unrepresentative.
For a measured alternative, suppose an illustrative appliance-only sample totals 12 kWh across three complete cooling days. Its average is 4 kWh per day. Repeating that average over 30 comparable use days gives 120 kWh and $24.00 at $0.20/kWh.
Keep the conditions, settings and schedule with the sample. A mild three-day period cannot establish energy use during a heatwave.
Use annual label mode on its stated basis
If the appropriate label provides annual kWh, the calculator can price that figure directly. An illustrative 400 kWh annual figure costs $80.00 at $0.20/kWh.
That is a cost for the stated label year, not a revised prediction based on the five-hour routine above. Select the correct cooling or heating figure and climate. Read the EU AC label guide for annual versus hourly information.
Compare units with compatible sources
A portable and a window unit may have different installation and operating conditions. Comparing unrelated nameplate ratings alone does not establish the cost of achieving equal comfort in your room.
Check whether a US specification gives an efficiency metric such as CEER rather than input watts. Read BTU/h versus electrical watts before entering a capacity or efficiency figure in a cost calculation.