Electricity Calculator

What this calculator does

The Electricity Calculator estimates how much energy an appliance uses and what that energy costs over a day, week, month, and year. It multiplies the power rating by the capacity percentage and operating hours, converts the result to kilowatt-hours, and multiplies by your electricity price.

Power can be entered in watts, kilowatts, BTU per hour, metric horsepower, or tons of refrigeration. Usage can be expressed per day, week, month, or year.

How to use this calculator

1. Enter the appliance's rated power and choose the power unit.
2. Enter the percentage of capacity at which it typically runs. Use 100 for a device that runs at its rated load.
3. Enter the usage amount and choose the time unit, such as hours per day or days per week.
4. Enter your electricity price in dollars per kilowatt-hour.
5. Click Calculate.

The default example is a 1,000 W appliance running at 100% capacity for 24 hours a day at $0.15 per kWh. It uses 24 kWh per day and costs $3.60 per day, $25.20 per week, $109.58 per month, and $1,314.90 per year.

Electricity cost formulas

Effective power (W) = rated power (W) × capacity / 100
Energy per day (kWh) = effective power / 1,000 × hours per day
Cost = energy (kWh) × price per kWh
Monthly energy = daily energy × 30.44
Yearly energy = daily energy × 365.25

The usage unit is converted to hours per day first. Minutes per day are divided by 60. Hours per week are divided by 7. Days per week are multiplied by 24 and divided by 7. Days per month and days per year use the same average month and year lengths as the cost conversion.

What the results mean

The daily, weekly, monthly, and yearly figures show the same underlying rate of use over different time spans. The monthly and yearly values are estimates based on average month and year lengths, not calendar-specific billing periods. The effective power is the rated power after the capacity percentage is applied, and the average use is the number of hours per day implied by your usage entry.

A label usually shows maximum power, not typical power. A refrigerator cycles its compressor, and a laptop rarely draws its full charger rating. Realistic capacity and usage estimates give better results than assuming continuous full-load operation.

Assumptions and limitations

• The calculator treats the capacity percentage and usage as constant. Real appliances cycle, and their draw varies with load and temperature.
• Monthly results use 30.44 days and yearly results use 365.25 days. Utility billing periods and rate structures can differ.
• The price is a single flat rate per kWh. It does not model tiered rates, time-of-use pricing, demand charges, taxes, or fees.
• Standby power, power-factor penalties, and charger efficiency losses are not included.
• BTU per hour is converted as 0.29307107 W, metric horsepower as 735.5 W, and a ton of refrigeration as about 3,516.85 W.

Frequently asked questions

How do I find the appliance's power rating?

Check the label or nameplate on the appliance, the owner's manual, or the manufacturer's website. The label usually lists watts, amperes, or BTU per hour. If it lists amperes and volts, multiply them to estimate watts for a resistive load.

Why is my bill different from the estimate?

The estimate uses one flat price and constant usage. Bills often include tiered rates, time-of-use pricing, taxes, transmission charges, and fees. Weather, occupancy, and appliance aging also change actual consumption.

Should I use hours per day or hours per week?

Use whichever unit matches how you think about the appliance. A space heater used two hours each evening is easiest as hours per day. A washing machine used five times a week might be easier as hours per week. The calculator converts both to a daily average.

Reference tables

Common appliances

Wattage varies by model, age, and settings. Check the appliance label or manual for a more precise value.

Example electricity cost at $0.15 per kWh

The cost column uses a $0.15 per kWh example rate. Replace it with the rate on your bill; utility rates vary by location and time of use.

Source

Reference: Calculator.net — Electricity Calculator.

Disclaimer

This calculator provides estimates for educational and planning purposes. Actual energy use and billed cost depend on the appliance, your usage patterns, and your utility's rate structure.