How to Calculate Watts to KWH

Watts and kilowatt-hours, or kWh, are units of power commonly employed to measure electrical power usage. Watts are usually encountered with light bulbs; for instance a 100 watt bulb. A kWh, on the other hand, is a unit that also includes time, and corresponds to 1,000 watts used for a full hour (think of ten such light bulbs burning together for one hour.) The kWh is the unit used to figure your electric company bill. By adding up the watts used and the amount of time they are used for, you can calculate kilowatt hours, and even make an estimate of your household efficiency or what your electric bills will be.

A watt is a unit of power.
  1. Find the wattage of the electrical items you are measuring. If the wattage is not printed on the unit, check the manual to see what the wattage is.

  2. Figure out, measure or estimate the number of hours each unit will run for the time period you are measuring.

  3. Multiply the wattage by the number of hours used to get a figure for watt-hours for each unit. As an example, if you have an appliance that runs at 200 watts, and you use it for 4 hours, that is 800 watt-hours.

  4. Add the total of watt-hours for all the units you are measuring.

  5. Divide the watt-hours total by 1,000 to get a figure for kWh. If your watt-hour total is 15,000, for instance, your kWh total is 15.

About the Author

Bill Brown has been a freelance writer for more than 14 years. Focusing on trade journals covering construction and home topics, his work appears in online and print publications. Brown holds a Master of Arts in liberal arts from St. John's University and is currently based in Houston.