Estimate electricity use and cost from appliance power, hours used, electricity price and number of days. For cycling appliances, use an average measured wattage or kWh figure where possible.
Fridges, dehumidifiers, heat pumps, ovens and other controlled appliances do not necessarily draw their rated power continuously. The result is therefore only as good as the average power or runtime assumption entered.
Electricity is billed in kilowatt-hours (kWh), not simply by the wattage printed on an appliance. Convert watts to kilowatts by dividing by 1,000, multiply by the time used, then multiply the resulting kWh by your electricity unit rate. For example, a 2,000 W heater running for one hour uses 2 kWh; a 200 W device running for ten hours also uses 2 kWh.
Simple resistive appliances such as kettles and electric heaters can be reasonably close to their rated power while actively heating. Fridges, ovens, dehumidifiers, washing machines and many other appliances cycle or change power during operation. For these, a measured kWh-per-cycle or average draw is usually more useful than nameplate watts.
A smart plug can provide a useful real-world figure for plug-in appliances within its rated load. For built-in or high-current appliances, use manufacturer energy data or appropriate metering rather than connecting an unsuitable monitoring device.
Run the calculator with your current unit rate, then test a higher and lower rate to understand sensitivity. If you are comparing two appliances, use the same amount of useful work: the same cooking task, drying load, room-heating requirement or hours of entertainment. A lower-wattage appliance is not automatically cheaper if it needs to run much longer.
The appliance worked examples provide realistic starting structures, but they are deliberately editable. Your own runtime, cycle energy and tariff should replace the illustrative values before you use the result for budgeting or a purchase decision.