Electricity Calculator
W
8
30
$
Monthly Cost$2.88
Monthly kWh24.00
Annual Cost$34.56
Every appliance has a wattage rating, and turning that rating into a real dollar figure on your power bill comes down to how long you run it and what your utility charges per kilowatt-hour. This calculator converts an appliance wattage and usage schedule into the energy it consumes in kilowatt-hours, then multiplies by your rate to show the monthly cost and the annual cost of leaving that device running.
Formula
monthly kWh = (watts × hours/day × days/month) ÷ 1000; monthly cost = kWh × rate; annual = monthly × 12
- watts
- Appliance power draw in watts
- hours/day
- Hours the device runs each day
- days/month
- Days per month the device is used
- rate
- Electricity price per kilowatt-hour in your currency
How it works
- Enter the appliance power draw in watts, how many hours per day you run it, and how many days per month it is in use.
- Multiply watts by hours and days, then divide by 1,000 to convert watt-hours into kilowatt-hours (kWh) consumed per month.
- Multiply the monthly kWh by your cost per kWh to get the monthly bill impact, and multiply that by 12 for the annual cost.
Worked example
A 100 W device run 5 hours a day, 30 days a month, at $0.15 per kWh.
- Monthly energy = (100 × 5 × 30) ÷ 1000 = 15,000 ÷ 1000 = 15 kWh.
- Monthly cost = 15 × $0.15 = $2.25.
- Annual cost = $2.25 × 12 = $27.00.
15 kWh per month costing $2.25, or $27.00 per year.
Frequently asked questions
- Where do I find an appliance wattage?
- Check the label or nameplate on the device, the manufacturer specifications, or a plug-in power meter. If only volts and amps are listed, multiply them (watts = volts × amps) to get the wattage.
- What is a kilowatt-hour?
- A kilowatt-hour (kWh) is the energy used by a 1,000-watt load running for one hour, and it is the unit utilities bill by. Running a 100 W device for 10 hours uses exactly 1 kWh (100 × 10 ÷ 1000).
- Does this include standby or phantom power?
- Only if you account for it. The calculator uses the wattage and hours you enter, so for devices that draw power on standby, add those idle hours at the lower standby wattage as a separate estimate.
- Why is my actual bill higher than this estimate?
- Real bills include fixed connection fees, taxes, tiered or time-of-use rates, and many appliances running at once. This tool isolates the cost of a single device, so it shows that device share, not your whole bill.