Electricity Cost Calculator: Appliance Load Inventory

How to calculate electricity cost by appliance

1. Enter each appliance’s quantity and electrical input watts. Use measured power or a documented operating value.
2. Enter the hours per day in the selected operating window.
3. Set duty percent to the fraction of that window drawing the entered power. Use 100% for continuous operation, or when watts already represents the average across that window.
4. Choose 1–366 days and enter your own price per kWh. Select the currency label, calculate and compare scenarios.

The initial values are illustrative assumptions, not average appliance consumption or a current electricity price. Selecting another currency changes the label only; it does not perform currency conversion.

Electricity cost formula

Daily kWh per row = quantity × watts ÷ 1,000 × hours per day × duty percent ÷ 100.

Period kWh = daily kWh × days. Energy cost = period kWh × price per kWh. Add the rows to obtain the inventory total. Power in kW describes a rate of use; energy in kWh includes elapsed time.

Six worked energy-cost examples

All examples use a hypothetical USD 0.15/kWh tariff and a 30-day period. The values demonstrate the formula; actual devices and tariffs vary.

Compare consumption before and after a change

Save a baseline scenario, then change one assumption. Reducing ten 10 W lights from five to three hours daily changes the 30-day result from 15 to 9 kWh. At the example tariff, energy cost falls from USD 2.25 to USD 1.35: a USD 0.90 difference. This is a calculated scenario, not a promised saving.

For cycling equipment, measure over a representative period. Enter either active watts with the measured duty fraction, or average watts with 100% duty. Applying a duty fraction to an already averaged watt value would undercount energy.

Electricity bill and calculator questions

Why does the result differ from my bill?

The calculator estimates energy charges at one flat rate. Bills may also contain fixed fees, taxes, tiered rates, demand charges and time-of-use prices. Unlisted devices, standby use and inaccurate operating assumptions also cause differences.

How do I handle off-peak and peak prices?

Calculate each tariff window separately with its matching hours and price, then add the energy charges. Do not treat a flat-rate estimate as a time-of-use bill.

Does a refrigerator use its rated power all day?

Not necessarily. A cycling appliance varies its draw over time. The 24-hour example uses an explicitly entered duty fraction; measure your own appliance or use reliable energy-label data.

Can I use COP instead of USD?

Yes. Select COP and enter your tariff in COP per kWh. The output is then in COP, without exchange-rate conversion.

Can I calculate a whole year?

Use 365 days, or 366 for a leap year. The model repeats the entered daily pattern for every day; use separate scenarios for seasonal or weekday differences.

Unit reference: the U.S. EIA explanation of watts, kilowatts and kilowatt-hours distinguishes instantaneous power from energy accumulated over time. The load inventories and worked scenarios above are this calculator’s own arithmetic examples.