Answer first
What this calculator tells you
Calculate the kilowatt-hours and cost of running any appliance from its wattage, hours and your rate. Find which appliance is worth replacing by pricing its running cost per month and per year. Formula: kWh = watts ÷ 1,000 × hours per day × days; cost = kWh × price per kWh. At the worked-example inputs, the cost for the period is $61. Holding every other input steady, moving electricity price per kwh from $0.14 to $0.20 moves the result from $50 to $72.
Transparent method
The formula
Find which appliance is worth replacing by pricing its running cost per month and per year.
Worked example
Example inputs
How to interpret the result
Running cost is a multiplication of power, time and price, and time is the number people misjudge. A 1,500 watt heater for eight hours a day uses 360 kilowatt-hours in a month and costs $61.20 at 17 cents. The same wattage on for one hour costs pennies. The annual figure shows what the habit costs, not what one evening costs.
At the worked-example inputs the cost for the period is $61. It rises with hours used per day, electricity price per kwh, power draw (watts) and days of use.
Real energy use depends on how the appliance or vehicle is actually run: duty cycle, weather, driving style, battery age and your utility's rate structure, including tiers and time-of-use pricing. Treat the result as a planning estimate and check it against your own bill or trip log.
Before you rely on it
What to check
Use the rate printed on your bill, including delivery charges. The energy-only rate leaves out part of what you actually pay.
The common error
Where people go wrong with electricity cost calculator
Treating the wattage on the label as steady draw. Thermostat-controlled devices cycle, so a fridge or heater draws its full wattage only part of the time.
Sensitivity evidence
How electricity price per kwh changes the cost for the period
Holding every other input at the worked-example value, moving electricity price per kwh from $0.14 to $0.20 moves the cost for the period from $50 to $72: a spread of $22, or 35% of the worked-example result.
| Electricity price per kWh | Cost for the period | Energy used (kWh) | Cost over a full year at this rate |
|---|---|---|---|
| $0.14 | $50 | 360 | $613 |
| $0.15 | $54 | 360 | $657 |
| $0.17worked example | $61 | 360 | $745 |
| $0.19 | $68 | 360 | $832 |
| $0.20 | $72 | 360 | $876 |
Every input, tested
Which input moves the cost for the period most
Of the 4 inputs, hours used per day moves the cost for the period most ($15 across the range tested) and days of use moves it least ($12).
| Input | Tested from | To | Cost for the period at each end | Swing |
|---|---|---|---|---|
| Hours used per day | 7 | 9 | $54 to $69 | $15 (25%) |
| Electricity price per kWh | $0.15 | $0.19 | $54 to $68 | $14 (24%) |
| Power draw (watts) | 1,350 | 1,650 | $55 to $67 | $12 (20%) |
| Days of use | 27 | 33 | $55 to $67 | $12 (20%) |
Two variables at once
Cost for the period by electricity price per kwh and power draw (watts)
Across the grid the cost for the period runs from $40 to $86. Moving electricity price per kwh from $0.14 to $0.20 shifts it by $22 at the middle column, and moving power draw (watts) from 1,200 to 1,800 shifts it by $24 at the middle row, so power draw (watts) is the bigger lever here.
| Electricity price per kWh \ Power draw (watts) | 1,200 | 1,500 | 1,800 |
|---|---|---|---|
| $0.14 | $40 | $50 | $60 |
| $0.15 | $43 | $54 | $65 |
| $0.17 | $49 | $61 | $73 |
| $0.19 | $55 | $68 | $82 |
| $0.20 | $58 | $72 | $86 |
The highlighted cell is the worked example: $61.
Step by step
The worked example, input by input
| Input | Value used | What it means |
|---|---|---|
| Power draw (watts) | 1,500 | Printed on the appliance's label or in its manual. |
| Hours used per day | 8 | Enter the hours used per day used in this calculation. |
| Electricity price per kWh | $0.17 | Found on your bill, in dollars per kilowatt-hour. |
| Days of use | 30 | Enter the days of use used in this calculation. |
| Cost for the period | $61 | |
| Energy used (kWh) | 360 | |
| Cost over a full year at this rate | $745 | |
Inputs, definitions and assumptions
Power draw (watts)
Printed on the appliance's label or in its manual. The prefilled worked-example value is 1,500.
Hours used per day
Enter the hours used per day used in this calculation. The prefilled worked-example value is 8.
Electricity price per kWh
Found on your bill, in dollars per kilowatt-hour. The prefilled worked-example value is $0.17.
Days of use
Enter the days of use used in this calculation. The prefilled worked-example value is 30.
How to use this calculator
- 1Verify the inputs. Gather power draw (watts), hours used per day, electricity price per kwh and days of use from your own documents; the prefilled values are examples.
- 2Save a baseline. The worked example puts the cost for the period at $61. Store your own version of it as Scenario A.
- 3Test one change. Start with hours used per day, the input with the biggest effect here: moving hours used per day from 7 to 9 takes the cost for the period from $54 to $69, a swing of 25% of the worked-example figure.
- 4Check the extremes. At half the example hours used per day (4) the cost for the period is $31; at double (16) it is $122.
People also ask
Frequently asked questions
How do you calculate electricity cost?
kWh = watts ÷ 1,000 × hours per day × days; cost = kWh × price per kWh. Enter electricity price per kwh in dollars. At the worked-example inputs the cost for the period is $61.
What does the electricity cost result mean?
Find which appliance is worth replacing by pricing its running cost per month and per year. At the worked-example inputs the cost for the period is $61. It rises with hours used per day, electricity price per kwh, power draw (watts) and days of use.
How much does electricity price per kwh change the cost for the period?
Holding every other input at the worked-example value, moving electricity price per kwh from $0.14 to $0.20 moves the cost for the period from $50 to $72, a spread of $22.
What are the limits of this electricity cost calculator?
Real energy use depends on how the appliance or vehicle is actually run: duty cycle, weather, driving style, battery age and your utility's rate structure, including tiers and time-of-use pricing. Treat the result as a planning estimate and check it against your own bill or trip log. The tables on this page test electricity price per kwh only from $0.14 to $0.20; a value outside that range is not tabulated here.
Which input moves the cost for the period most in the electricity cost calculator?
Ranked by how far each moves the cost for the period across the range tested: hours used per day ($15, 25%), electricity price per kwh ($14, 24%), power draw (watts) ($12, 20%) and days of use ($12, 20%).
If I double hours used per day in the electricity cost calculator, does the cost for the period double?
Doubling it from 8 to 16 takes the cost for the period from $61 to $122, which is 2.00 times the worked-example figure. So the result scales almost exactly in proportion. Halving it to 4 gives $31.
How much does power draw (watts) matter in the electricity cost calculator?
The worked example uses 1,500. With the other inputs left at the worked example, moving power draw (watts) from 1,350 to 1,650 takes the cost for the period from $55 to $67, a swing of 20% of the worked-example figure.
How much does hours used per day matter in the electricity cost calculator?
The worked example uses 8. Holding every other input at its worked-example value, moving hours used per day from 7 to 9 takes the cost for the period from $54 to $69, a swing of 25% of the worked-example figure.
How much does days of use matter in the electricity cost calculator?
The worked example uses 30. With the other inputs left at the worked example, moving days of use from 27 to 33 takes the cost for the period from $55 to $67, a swing of 20% of the worked-example figure.
Which inputs change the energy used (kwh) in the electricity cost calculator?
At the worked-example inputs it is 360. Power draw (watts) takes it from 324 to 396, hours used per day takes it from 315 to 405 and days of use takes it from 324 to 396.
Which inputs change the cost over a full year at this rate in the electricity cost calculator?
At the worked-example inputs it is $745. Power draw (watts) takes it from $670 to $819, hours used per day takes it from $652 to $838 and electricity price per kwh takes it from $657 to $832.
Is my electric rate the same for every kilowatt-hour?
Not always. Many utilities charge tiered or time-of-use rates and add delivery fees and taxes. For an all-in rate, divide your whole bill by the kilowatt-hours you used.
What is a kilowatt-hour?
The energy used by a 1,000 watt device running for one hour. A 100 watt bulb left on for ten hours uses one.
Why is standby power worth counting?
Devices left plugged in draw a few watts around the clock. Across a house of chargers, screens and set-top boxes that adds up, and it runs all 8,760 hours of the year.
Sources and evidence
Free Calculators Online is independent and is not affiliated with or endorsed by the source organizations. Educational estimates only.