Enter an appliance's power draw, how long you run it, and your electricity rate. You get the daily, monthly, and yearly cost to run it, with the math shown so you can compare appliances or decide what to unplug.
Watts measure how fast an appliance pulls power right now. A kilowatt-hour (kWh) is what your utility actually bills you for: it is 1,000 watts running for one hour. So a 1,500 watt heater run for one hour uses 1.5 kWh. Multiply that by your rate per kWh and you have the cost. The calculator just does this for a full day, month, and year.
Check the nameplate, the small metal or printed label usually on the back, bottom, or inside the door. It lists the rated watts, or it lists volts and amps, in which case watts equal volts times amps. The manual and the manufacturer's website list the same numbers. If a device only shows a range, use the higher figure for a worst-case estimate, then trim your hours per day to match how you really use it.
Anything that makes heat or runs a motor dominates your bill. Electric heaters, water heaters, dryers, ovens, and air conditioners draw the most watts, so even short daily use adds up fast. Lights, chargers, and small electronics draw little and cost pennies. When you want to cut a bill, start with the high-wattage heating and motor appliances and look at the hours, not the gadgets.