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Smart Plug Energy Cost Calculator

Turn a smart plug power reading into daily energy use and the monthly and annual cost of whatever is plugged into it.

About Smart Plug Energy Cost Calculator

Power in watts times hours of operation gives watt-hours; dividing by 1,000 converts to the kilowatt-hours your bill is denominated in. Carbon is estimated at roughly 0.4 kg CO2e per kWh, a mid-range grid intensity. An always-on appliance looks trivial at 10 W until it is multiplied by 8,760 hours — running cost, not purchase price, dominates the lifetime total.

Formula

Smart Plug Energy Cost

kWh = watts × hours ÷ 1,000; cost = kWh × tariff

Measured appliance power draw
Continuous power draw
tariff
Price paid per kilowatt-hour

Worked example

With the default values below, Smart Plug Energy Cost Calculator returns Monthly Running Cost of $1.62. Change any input above and every figure here is recalculated in your browser.

Inputs used

Measured appliance power drawminimum 0 W
60 W
Number of devicesminimum 1
1
Hours running per dayaccepts 0–24 h
6 h
Electricity priceminimum 0 per kWh
0.15 per kWh

Results

Monthly Running Cost
$1.62
Annual Running Cost
$19.71
Energy Used per Day
0.360 kWh
Energy Used per Year
131.4 kWh
Estimated CO2e per Year
52.6 kg

Step by step

  1. 1Values used
  2. 2Smart Plug Energy Cost
  3. 3Monthly Running Cost= 1.62
  4. 4Annual Running Cost= 19.71
  5. 5Energy Used per Day= 0.360 kWh
  6. 6Energy Used per Year= 131.4 kWh
  7. 7Estimated CO2e per Year= 52.6 kg

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Smart Plug Energy Cost calculated?

kWh = watts × hours ÷ 1,000; cost = kWh × tariff Power in watts times hours of operation gives watt-hours; dividing by 1,000 converts to the kilowatt-hours your bill is denominated in. Carbon is estimated at roughly 0.4 kg CO2e per kWh, a mid-range grid intensity.

Why does Smart Plug Energy Cost matter?

An always-on appliance looks trivial at 10 W until it is multiplied by 8,760 hours — running cost, not purchase price, dominates the lifetime total.

What values do I need to enter?

This calculator takes 4 inputs: Measured appliance power draw, Number of devices, Hours running per day, Electricity price. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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