Estimated running cost of an appliance, from its wattage, daily usage and your electricity rate.
Electricity is billed in kilowatt-hours (kWh), but appliance power is usually rated in watts. Multiplying watts by hours used gives watt-hours, and dividing by 1000 converts that to kilowatt-hours before it's multiplied by your rate.
Check the appliance's nameplate, spec sheet, or box — it's usually listed directly in watts. If only amps and voltage are given, multiply them together (Watts = Volts × Amps) to get an approximate wattage to enter here.
They simply scale the daily cost by 30 (for a month) and 365 (for a year), assuming the appliance is used for the same number of hours every day — actual usage that varies day to day will change the real monthly and yearly totals.