How to Calculate the Wattage of an Appliance

First we must understand that using this formula will show you the MAXIMUM wattage a product can use. Most appliances have multiple settings so the actual usage will vary. For instance, the maximum power a stove oven can use is when all burners and the oven are turned on. The appliance will use less than its maximum rated wattage when only one burner is turned on.

The video above shows several formulas on how to calculate the wattage used by any electrically powered product. It may get a little complicated so here are the basic formulas.

Manual Calculation

  • •   Watts = Volts x Amperes
  • •   1 kilowatt (kW) = 1000 Watts
  • •   Kilowatt-Hours (kWh) = kW x hours used
  • •   Cost = kWh x cost per kWh


  • •   Motor 120 volts, 6 amps on for 12 hours at $0.068 per kWh for 30 days
  • •   120 volts x 6 Amps = 720 Watts
  • •   720 Watts = 0.72kW
  • •   0.72kW x 12 hours = 8.64 kWh used in 12 hours
  • •   8.64 kWh x $0.068 per kWh = $0.58 cost to operate for 12 hours
  • •   0.58 x 30 days = $17.40 cost to operate for 12 hours each day for 30 days

If this seems a little complicated, feel free to visit the NOTL Public library on Anderson Lane and borrow one of our Watt readers. They are easy-to-use devices that will help you measure the electricity used by the electrical appliances in your home. All you need to do is plug a device into the watt reader and it will show you how much kW it is consuming. For more information please click here.