Appliance Energy Calculator Formula

Understand the math behind the appliance energy calculator. Each variable explained with a worked example.

Use the Appliance Energy Calculator

Formulas Used

Annual Cost

annual_cost = annual_kwh * rate_per_kwh

Monthly Cost

monthly_cost = annual_kwh * rate_per_kwh / 12

Annual Energy Use

annual_energy = annual_kwh

Daily Energy Use

daily_kwh = wattage * hours_per_day / 1000

Variables

VariableDescriptionDefault
wattageAppliance Wattage(watts)1500
hours_per_dayHours Used per Day(hours)3
days_per_yearDays Used per Year(days)365
rate_per_kwhElectricity Rate(USD/kWh)0.15
annual_kwhDerived value= wattage * hours_per_day * days_per_year / 1000calculated

How It Works

How to Calculate Appliance Energy Cost

Every electrical appliance has a wattage rating that determines how much energy it uses.

Formula

Annual kWh = Wattage * Hours/Day * Days/Year / 1,000

Annual Cost = Annual kWh * Rate per kWh

Common Appliance Wattages

  • Space heater: 1,500W
  • Hair dryer: 1,200W
  • Refrigerator: 150W (average)
  • LED bulb: 10W
  • Desktop computer: 200W

    • Worked Example

    A 1,500W space heater used 3 hours/day for 365 days at $0.15/kWh.

    wattage = 1500hours_per_day = 3days_per_year = 365rate_per_kwh = 0.15
    1. 01Annual kWh: 1,500 * 3 * 365 / 1,000 = 1,642.5 kWh
    2. 02Annual cost: 1,642.5 * $0.15 = $246.38
    3. 03Monthly cost: $246.38 / 12 = $20.53
    4. 04Daily kWh: 1,500 * 3 / 1,000 = 4.5 kWh

    Ready to run the numbers?

    Open Appliance Energy Calculator