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Electricity Cost Calculator

Work out how much it costs to run an appliance or device per day, month and year, from its watts, hours of use and your electricity rate.

Results

ItemValue
Check your electricity bill for your real rate per kWh, including delivery charges. Many devices use less than their rated watts most of the time, so real costs can be lower.

Quick Answer

Electricity cost = watts × hours ÷ 1,000 × price per kWh. A 1,500-watt space heater used 4 hours a day uses 6 kWh. At $0.17 per kWh, that is $1.02 a day, about $31.03 a month or $372.30 a year.

Last updated: 2 November 2026 ·How we calculate this: kilowatt-hours times your rate

Table of Contents

How This Electricity Cost Calculator Works

Enter a device’s power in watts, how many hours a day it runs, and your electricity rate. The calculator turns watts and hours into kilowatt-hours (kWh), the unit on your bill, then multiplies by your rate.

Quick explanation: kWh = watts × hours ÷ 1,000, and cost = kWh × rate.

  • Watts: on the device label, charger or manual.
  • Rate: on your bill, in dollars or cents per kWh.
  • Devices: multiply for several identical items, such as light bulbs.

How to Use the Electricity Cost Calculator

  1. Find the device’s power in watts on its label or charger.
  2. Enter how many hours a day it is used.
  3. Enter your electricity rate from your bill, in dollars per kWh.
  4. Enter how many of the same device you use, then press Calculate.
  5. Read the cost per day, month and year, and the energy used.

Core Formulas

  • Energy per day: kWh = watts × hours ÷ 1,000
  • Cost per day: kWh × price per kWh
  • Cost per month: daily cost × 365 ÷ 12
  • Cost per year: daily cost × 365

If a label shows amps instead of watts, multiply amps by volts. In the US, most outlets supply about 120 V.

Key Terms

  • Watt (W): a unit of power, the rate at which energy is used.
  • Kilowatt-hour (kWh): 1,000 watts used for one hour, the unit on electricity bills.
  • Rate: the price you pay per kWh.
  • Standby power: power a device uses while switched off but still plugged in.

Worked Example

Twenty 10-watt LED bulbs are on for 5 hours a day, at $0.17 per kWh.

  • kWh per day = 10 × 5 × 20 ÷ 1,000 = 1 kWh
  • Cost per day = 1 × 0.17 = $0.17
  • Cost per year = 0.17 × 365 = $62.05

Real-Life Examples

  • Space heater: 1,500 W for 4 hours a day costs about $31.03 a month at $0.17 per kWh.
  • Switching bulbs: replacing a 60 W bulb with a 9 W LED, used 5 hours a day, saves about $15.82 a year per bulb.
  • Gaming PC: a 400 W computer used 3 hours a day costs about $74.46 a year.
  • Electric car charging: adding 30 kWh a week at $0.17 costs about $5.10 a week, or $265.20 a year.

Watts vs Kilowatt-Hours

  • Watts (W): how fast a device uses power at a moment.
  • Kilowatt-hours (kWh): how much energy it uses over time. You pay for kWh.
  • The link: 1,000 watts running for 1 hour uses 1 kWh.
  • Example: a 100 W bulb for 10 hours uses 1 kWh, the same as a 1,000 W heater for 1 hour.

Yearly Cost by Watts and Hours

At $0.17 per kWh.

Watts1 hour/day4 hours/day8 hours/day24 hours/day
10 W$0.62$2.48$4.96$14.89
60 W$3.72$14.89$29.78$89.35
100 W$6.21$24.82$49.64$148.92
500 W$31.03$124.10$248.20$744.60
1,000 W$62.05$248.20$496.40$1,489.20
1,500 W$93.08$372.30$744.60$2,233.80

What Changes Your Cost

  • Rate plans: some plans charge more at peak times.
  • Cycling: fridges, heaters and AC units switch on and off, so they rarely draw full power all the time.
  • Standby power: TVs and chargers can use a little power even when off.
  • Efficiency: newer, efficient models usually use less for the same job.

Common Mistakes to Avoid

  • Using only the energy charge. Delivery and other per-kWh fees raise your real rate.
  • Assuming full power all the time. Thermostat-controlled devices cycle on and off.
  • Mixing cents and dollars. 17 cents per kWh is 0.17.
  • Forgetting standby use. Devices left plugged in can add up.
  • Ignoring seasons. Heating and cooling costs change through the year.

Frequently Asked Questions

Multiply watts by hours used, divide by 1,000 to get kWh, then multiply by your price per kWh.

At $0.17 per kWh, about $0.26 an hour.

It varies by model. Check the yellow EnergyGuide label, which shows yearly kWh use.

Divide your total bill by the kWh used that month. This gives an all-in rate including fees.

Only if your plan has lower night or off-peak rates. Check your plan.

Multiply amps by volts. A 10 A device on 120 V uses about 1,200 W.

A 100 W TV on for 24 hours uses 2.4 kWh, about $0.41 a day at $0.17 per kWh.

A little. Devices in standby can use a few watts each, which adds up over a year across many devices.

Use a plug-in electricity usage monitor. It shows the actual watts and kWh over time.

Heating, cooling and water heating are usually the biggest users.

References & Sources

SourceUsed ForLink
Wikipedia, Kilowatt-hour The unit used on electricity bills. https://en.wikipedia.org/wiki/Kilowatt-hour
U.S. Energy Information Administration, Electricity explained How electricity is measured and priced. https://www.eia.gov/energyexplained/electricity/