Electricity Cost Calculator
Estimate the running cost of any appliance from its wattage, daily usage hours, and your electricity rate — with daily/weekly/monthly/yearly energy and cost, plus a yearly CO2 estimate.
Input
Power rating of the device, in watts. Check the label or spec sheet.
Your price per kilowatt-hour. Used when the preset is set to Custom.
Total identical devices running under the same conditions.
Output
| Period | Energy (kWh) | Cost |
|---|---|---|
| No data yet | ||
Guides
What does this calculator do?
The Electricity Cost Calculator turns an appliance's wattage and how long you run it into the real cost of keeping it on — broken down by day, week, month, and year — plus an estimate of the CO2 emissions that usage produces. It is the fast way to answer "how much does this thing actually cost me to run?" for anything from a phone charger to a space heater.
How the numbers are worked out:
- Daily energy in kilowatt-hours:
dailyKwh = (watts × hoursPerDay × devices) ÷ 1000. - The other periods scale from that: weekly
× 7, monthly× 30(a nominal 30-day month), yearly× 365. - Cost for each period is
energyKwh × ratePerKwh. - Yearly CO2 is
yearlyKwh × 0.417 kg/kWh, a global-average grid emissions factor, also shown in tonnes.
Worked example: a 100W device left on 8 hours a day uses (100 × 8 × 1) ÷ 1000 = 0.8 kWh per day. At $0.12/kWh that is about $0.10 a day, $2.88 a month, and $35.04 a year — and roughly 121.8 kg of CO2 over the year.
How to use it
- Enter the device wattage (watts) — usually printed on the device, its power supply, or the spec sheet.
- Enter the hours per day you run it (up to 24).
- Pick a rate preset for your region, or leave it on Custom and type your own price per kWh from your utility bill.
- Set the number of devices if you are running several identical ones.
The table and CO2 estimate update as you type. You can copy the CO2 figure or copy/download the full breakdown table as CSV.
Where do I find my electricity rate?
It is on your utility bill, usually shown as a price per kWh (kilowatt-hour). If you cannot find it, the regional presets give a reasonable average for the US, UK, EU, Australia, Canada, and India. The rate is currency-agnostic — enter your local price and the costs come out in that same currency (the "$" shown is just a label).
Why is my monthly cost different from my actual bill?
This tool models one device at a constant power draw and uses a nominal 30-day month and 365-day year. Real bills bundle many devices, standby draw, tiered or time-of-use pricing, taxes, and fixed connection fees. Treat the result as a solid estimate for a single appliance, not a replacement for your metered bill.
How accurate is the CO2 estimate?
It uses a single global-average factor of 0.417 kg CO2 per kWh. Your actual grid may be much cleaner (lots of renewables/nuclear) or dirtier (coal-heavy), so the true figure can vary substantially. It is meant for rough comparison, not carbon accounting.
Privacy
This calculator runs entirely in your browser. Your wattage, hours, rate, and device count are never sent to a server, logged, or stored — the math happens locally on your device.