Standby Power Calculator Formula

Understand the math behind the standby power calculator. Each variable explained with a worked example.

Use the Standby Power Calculator

Formulas Used

Annual Standby Cost

annual_cost = annual_kwh * rate_per_kwh

Monthly Cost

monthly_cost = annual_kwh * rate_per_kwh / 12

Annual Standby Energy

annual_energy = annual_kwh

Total Standby Load

total_watts = total_standby_watts

Variables

VariableDescriptionDefault
num_devicesNumber of Devices15
avg_standby_wattsAverage Standby Wattage(watts)5
rate_per_kwhElectricity Rate(USD/kWh)0.15
total_standby_wattsDerived value= num_devices * avg_standby_wattscalculated
annual_kwhDerived value= total_standby_watts * 8760 / 1000calculated

How It Works

How to Calculate Standby Power Cost

Standby power (phantom load) is electricity consumed by devices when they are turned off but still plugged in.

Formula

Annual kWh = Devices * Avg Standby Watts * 8,760 hours / 1,000

Annual Cost = Annual kWh * Rate

Common Standby Draws

  • TV: 5-10W
  • Game console: 2-25W
  • Cable box: 15-30W
  • Phone charger: 0.5-2W
  • Microwave (with clock): 3-5W

    • Worked Example

    15 devices averaging 5W standby power at $0.15/kWh.

    num_devices = 15avg_standby_watts = 5rate_per_kwh = 0.15
    1. 01Total standby: 15 * 5 = 75 watts
    2. 02Annual kWh: 75 * 8,760 / 1,000 = 657 kWh
    3. 03Annual cost: 657 * $0.15 = $98.55
    4. 04Monthly cost: $98.55 / 12 = $8.21

    Ready to run the numbers?

    Open Standby Power Calculator