kWh = (watts ÷ 1,000) × hours. Estimated cost = kWh × your entered price per kWh.
What this calculator tells you
This estimate separates energy use from the price charged for that energy. Watts describe power at a moment; kilowatt-hours (kWh) describe energy accumulated over time. The distinction matters because an appliance that draws 1,000 watts for one hour uses about 1 kWh, while a 100-watt device running for ten hours uses the same amount.
How to get a useful estimate
- Find the rated input power on the appliance label or manual. Do not use a motor’s output power when the label lists electrical input.
- Estimate average hours of operation. For a refrigerator or air conditioner, the compressor may cycle instead of drawing full power continuously.
- Enter the actual per-kWh rate from your bill. If your bill contains a fixed service charge, taxes, tiered rates, or time-of-use prices, the simple estimate will not reproduce the complete bill.
- Compare the monthly result with your bill over a similar period. A mismatch is a useful reason to inspect assumptions, not proof that either number is wrong.
Worked example
A 500-watt device used for four hours per day consumes 0.5 kW × 4 hours = 2 kWh per day. Over 30 days that is 60 kWh. At an example rate of 0.20 currency units per kWh, the energy charge would be 12 currency units. This excludes fixed charges and taxes.
Limits to keep in mind
The calculation is only as accurate as the power and runtime values entered. Variable-speed equipment, thermostatically controlled appliances, standby modes, and changing workloads can make actual consumption different from a simple rated-power estimate. A plug-in energy meter or a utility interval meter can improve the input data where appropriate.
Related tools and guides
For the basic relationship between watts and kWh, read Watts vs. kilowatt-hours. You can also use the Home Energy Planner to combine several devices in one estimate.