Power is a rate measured in watts; billed energy is commonly measured in kilowatt-hours. The Power Consumption Calculator makes a usage scenario explicit.
Check the units
A constant 100 W for 5 hours uses 100 / 1000 × 5 = 0.5 kWh. Repeated for 30 days, that is 15 kWh. At an illustrative 0.20 per kWh, the energy charge is 3.00 currency units, excluding fixed charges and other tariff components.
Maximum power is not average power
A heater cycles, a refrigerator changes load and a laptop charger’s maximum rating does not equal average laptop consumption. Use measured energy over a representative period when possible, rather than assuming maximum draw whenever a device is plugged in.
Check flat, tiered or time-dependent rates and include standby use separately when relevant. Mixing W and kW creates a factor-of-1,000 error.
The estimate covers the modeled appliance. Other devices, taxes and service charges explain why it will not reproduce an entire household bill.