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Bill Calculation

If you think your electric usage has increased in certain months, first check to see what new electric items you may be using. Run some calculations on how much energy a certain item may use. Your question, "how did I use so much electricity" may be answered with a few simple calculations.

By using OHM'S LAW, electric customers can calculate electrical usage of their electrical products. The nameplate on your tool has key information needed to calculate its electrical usage. In OHM'S LAW, there are four electrical factors to use.

Voltage or Power = V
Amps or Current = I
Ohms or Resistance = R
Watts = P

Use watts to calculate electric usage. Your electric meter measures your electric consumption in kWh, or Kilo Watt Hours. Every time an electric meter measures One thousand Watts of electric use in one hour, the meter will record one kilo watt hour. This may sound complicated but after calculating a few products, it will become easy. Remember, it takes one thousand watts in one hour, for the electric meter to record one kWh. Check out the examples of some electric products below. Remember 1000 watts equals ONE kilowatt.



If the nameplate specifies wattage:

  • 100 watt light bulb = 10 hours of use to equal one kilo watt-hour.
    100 watts x 10 hours = 1000 watts or one kWh

  • One plug in electric heater rated at 1000 watts = 1 hour of use equals one kilo watt-hour.
    1000 watts x 1 hour = 1000 watts or one kWh

If the nameplate does not specify wattage, it must be calculated:

The name plate on an electric tool rates it at 120 volts drawing 10 amps at full load. Use the following example to calculate watts.

  • 120 volts x 10 amps = 1,200 watts = this tool would use 1.2 kWh per hour of use.

If the name plate states that this appliance is rated at 240 volts and will draw 10 amps at full load.

  • 240 volts x 10 amps = 2,400 watts = this appliance would use 2.4 kWh per hour of use.

To calculate the monthly cost of operation for a 500 watt tank heater that operates for 12 hours a day, use the following formulas:

  • 500 watts x 12 hours = 6,000 watts per day or 6 kWh per day.
    6 kWh x .10680 cents per kWh = .64 cents per day.
    .64 cents per day x 30 days = $19.20 per month cost to use this tank heater.

This calculation can be used in this way for anything we use in our homes and businesses.

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