Quick answer
Electricity Cost Calculator: what it calculates
Electricity Cost Calculator calculates electricity cost from watts, hours per day and days. The core method is Cost = watts / 1000 x hours per day x days x electricity rate per kWh.
Everyday Calculators
Electricity Cost Calculator
Use this electricity cost calculator to estimate appliance energy use and cost from watts, hours per day, days used, and cents per kWh.
Reviewed May 25, 2026EstimateFormula shown
ResultElectricity cost
InputsWatts, Hours per day, Days, Electricity rate
FormulaElectricity cost formula
Live calculator
Electricity cost
Estimated cost$24.30
135 kWh over 30 days.
Daily cost$0.81
Average cost per day for the usage pattern.
30-day estimate$24.30
Daily cost scaled to a 30-day month.
Formula
Electricity cost formula
Cost = watts / 1000 x hours per day x days x electricity rate per kWhUse the wattage listed on the device or a measured average. Actual energy use can vary by setting and duty cycle.
How to use
Steps
- Enter the appliance wattage.
- Enter how many hours per day it runs.
- Enter the number of days to estimate.
- Enter your electricity rate in cents per kilowatt-hour.
Example
Sample calculation
Watts1,500
Hours/day3
Rate18 cents/kWh
30-day cost$24.30
Calculator use
Best for
- Quick electricity cost from watts, hours per day and days.
- Quick everyday math with the result and formula in one place.
- Shopping, date, time, unit, school, or household comparisons.
- A fast check before moving the numbers into a spreadsheet.
Before relying on it
Check first
- Entering watts, hours per day and days from different time periods or scenarios.
- Mixing units, dates, or original values across the same calculation.
- Rounding early and then using the rounded number in another step.
- Copying a result without checking whether the inputs match the real-world question.
Benchmarks
How to read the result
The calculator is a decision aid, not a fixed rule. Use the output to compare scenarios and document your assumptions.
Under 100WLow draw
Common for LED bulbs, chargers, small fans, and efficient electronics.
500W - 1,500WMedium to high draw
Common for space heaters, microwaves, hair dryers, and kitchen appliances.
Runs many hoursCost adds up
Low wattage devices can still cost more when they run all day.
Calculator accuracy
Methodology and assumptions
The formula, inputs, example, and limitations are shown so the result is checkable, not just a number in a box.
Formula
Cost = watts / 1000 x hours per day x days x electricity rate per kWh
Inputs used
Watts, Hours per day, Days, Electricity rate
Limitations
Results are estimates for quick planning and should be checked before important financial, legal, tax, health, or business decisions.
Last reviewed
May 25, 2026
Cite this page
Toolkit Shelf. Electricity Cost Calculator. Retrieved May 25, 2026, from https://toolkitshelf.com/tools/electricity-cost-calculator
FAQ
Common questions
How do I calculate appliance electricity cost?
Divide watts by 1,000 to get kilowatts, multiply by hours used, then multiply by your cost per kWh.
What is a kilowatt-hour?
A kilowatt-hour is 1,000 watts used for one hour. Electric bills usually charge by kWh.
Why is the result only an estimate?
Many devices cycle on and off or use different power levels, so listed wattage may not equal average wattage.