The kilowatt-hour is the basic measurement used to calculate your bill. Any electronic device has a certain amount of electricity it needs to function, also known as its wattage.
For example, the average ceiling fan is 50 watts. If you use that fan for 20 hours in 1 month, your ceiling fan will have consumed 1 kilowatt-hour. You can do the math by multiplying the wattage (50) by the number of hours used (20), and then dividing the sum by 1,000.
Here’s another example: If you run a 1,500-watt space heater for 8 hours a day, every day of the month, that will use up about 360 kWh for the month. Here’s the math: You used it for a total of 240 hours that month, because 8 hours a day x 30 days = 240. So, multiply the wattage (1,500) by the number of hours used (240), and then divide that by 1,000.