Electricity Cost Calculator
Calculate the electricity cost of an appliance from its wattage and usage time. You enter your own per-kWh unit price from your utility bill, rather than the tool assuming any specific utility's rate. Includes rough wattage presets for common appliances like refrigerators and air conditioners. All calculations run in your browser, so nothing you enter is sent anywhere.
Everything you enter is processed entirely in your browser and is never sent anywhere.
Enter power consumption, usage time, and unit price, then press "Calculate".
- Cost
- Energy used
Monthly estimate (30-day basis)
- Cost
- Energy used
Yearly estimate (365-day basis)
- Cost
- Energy used
How to use
- Enter the power consumption (W). Choosing an appliance preset fills this in automatically, and you can still edit it freely.
- Enter the usage time (hours) and the unit price (yen/kWh) shown on your electricity bill.
- Press "Calculate" to see the cost. Enter a daily usage time too, and you'll also get monthly and yearly estimates.
How it works
Formula
Energy used (kWh) = Power (W) x Usage time (h) / 1000
Cost (yen) = Energy used (kWh) x Unit price (yen/kWh)
Watts are converted to kilowatts by dividing by 1000, multiplied by the usage time to get kWh, then multiplied by the unit price to get the cost.
Why we don't hardcode a utility's rate
Per-kWh unit prices vary by utility company and plan, and change nearly every month due to fuel cost adjustments and renewable energy surcharges. Baking a specific rate into the tool risks showing a figure that no longer matches reality. Instead, this tool asks you to enter the unit price shown on your own electricity bill. This also means no external rate data needs to be fetched — everything from input to calculation stays inside your browser.
About the appliance presets
The preset wattage values are representative figures based on the ranges published by Only Style, an electrical parts retailer, in their household appliance power consumption list (https://eco-power.jp/power_list.html, in Japanese). Actual power consumption varies substantially by model, age, and operating mode (air conditioners in particular can differ by an order of magnitude between standby and full-power cooling). For an accurate figure, check the rated power consumption printed on your actual appliance or in its manual, and enter that value instead.
About the monthly/yearly estimate
If you enter a "daily usage time", the tool multiplies the single-use energy and cost by 30 (monthly) and 365 (yearly) as a simple estimate. It does not account for variations in actual usage days or hours, so treat it as a rough guide only.
FAQ
Is the power consumption or unit price I enter sent to a server?
No. All calculations happen entirely inside your browser.
Why isn't the unit price field pre-filled?
Per-kWh unit prices vary widely by utility and plan and change frequently. Pre-filling a value risked being mistaken for an actual rate, so the field is left blank on purpose. Please enter the unit price shown on your own electricity bill.
How accurate are the appliance presets?
They are rough guides only, based on representative values from a published wattage range (Only Style's appliance power consumption list). Actual consumption varies a lot by model, age, and operating mode -- air conditioners especially can vary enormously depending on how hard they're running. For an accurate cost, check the rated wattage on the appliance itself or its manual and enter that value instead.
Does this include the base charge or fuel adjustment fees?
No. This tool only estimates the energy charge (power x time x unit price). Your actual electricity bill also includes a base charge (based on your contracted amperage), fuel cost adjustments, and renewable energy surcharges, so the total will differ from what's on your bill.
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