Electricity Cost & Energy Calculator
Turn power (W, or A × V) and usage time into energy in kWh and electricity cost per day, month and year. The rate is editable for your own tariff, and the tool converts between kWh, J, MJ and kcal.
Enter the rate from your bill. The default 31 ¥/kWh is the Japanese industry guideline value (revised July 2022).
Try an example
Enter the values and press Calculate.
Done
Electricity Cost & Energy Calculator
How to use
- 1
Choose the calculation
Select electricity cost or energy unit conversion.
- 2
Enter power and usage
Enter power in W (or current A and voltage V), hours per day and your rate in ¥/kWh.
- 3
Check the result
See energy and cost per day, month and year, conversions to J, MJ and kcal, and the working.
Features
- Energy and cost per day, month and year from power and usage time
- Enter power directly in W/kW or from current A and voltage V
- Editable rate (¥/kWh) so the result matches your tariff
- Energy unit conversion for kWh, Wh, J, kJ, MJ and kcal
- See the working and the monthly energy in other units
- Runs entirely in your browser; no sign-up and nothing uploaded
Use cases
Compare appliances
See the monthly cost of a hair dryer, air conditioner and more at the same rate.
Plan savings
Check how changing usage hours affects the bill and where to cut first.
Learn the units
Practise the relationships between W, kW, kWh, J and cal with real numbers.
Details
Energy in kWh is power in kW multiplied by time in hours. A 1200 W (1.2 kW) hair dryer used for 0.2 h (12 minutes) uses 1.2 × 0.2 = 0.24 kWh. The cost is energy × rate, so 0.24 × 31 = 7.44 at 31 per kWh.
The rate depends on your tariff, so the tool lets you change it. The default 31 per kWh is the guideline value published by the Japan Electrical Fair Trade Council on 22 July 2022 (previously 27). Check your bill or your utility account for the actual rate.
The estimate covers the energy charge only. Standing charges, fuel-cost adjustments, renewable levies and taxes are not included. Appliances such as air conditioners and refrigerators vary their draw with operating conditions; a refrigerator cycles its compressor, so if you know the daily energy (Wh/day) use that instead.
Energy converts as 1 kWh = 3.6×10⁶ J = 3.6 MJ, and 1 Wh = 3600 J. In heat units, 1 kWh ≈ 860 kcal (1 cal = 4.184 J). Note that W is power and Wh/kWh is energy — they are different quantities.
FAQ
What is the difference between kW and kWh?
kW is power, the rate of energy use, while kWh is energy, the total amount used. A 1000 W appliance running for one hour uses 1 kWh. Tariffs are usually quoted per kWh.
Which rate should I use?
Use the energy charge per kWh from your bill or utility account. The 31 per kWh guideline was set by the Japan Electrical Fair Trade Council in July 2022; actual rates differ by utility, plan and usage.
Why does my bill differ from this estimate?
This covers the energy charge only, excluding standing charges, fuel-cost adjustments, renewable levies and taxes. Appliance power also varies with operating conditions, so the catalogue figure is not constant.
Does it work for air conditioners and refrigerators?
Yes, but their actual draw varies — air conditioners with temperature and load, refrigerators by cycling the compressor. If you know the annual energy consumption or daily kWh from the product label, enter that in the energy conversion mode instead.
How many joules is 1 kWh?
1 kWh = 3.6×10⁶ J = 3.6 MJ, or about 860 kcal using 1 cal = 4.184 J. A 1 kWh electric heater delivers roughly 860 kcal of heat, which you can compare with the heat calculator.
Can I estimate standby power?
If you know the standby wattage, enter it as the power, 24 h per day and 30 days per month to estimate the monthly cost. Actual standby power varies by device; use the manual or a power meter for real values.
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All processing happens in your browser. Your files are never uploaded.
Verified: Known values (1200 W × 0.2 h giving 7.44 per day, 600 W × 8 h giving 4.8 kWh/day and 4,464 per month, 10 W × 8 h giving 2.48 per day, 150 W × 24 h giving 111.6 per day, 1400 W × 0.1 h giving 4.34 per day, 100 V × 10 A giving 1000 W, and 1 kWh giving 3.6×10⁶ J, 1,000 Wh and 860.4 kcal) plus invalid, out-of-range days and zero-rate errors are covered by browser tests
Did you know?
1 kWh is the energy used by a 1000 W appliance running for one hour, equal to 3.6×10⁶ J (3.6 MJ) or about 860 kcal (1 cal = 4.184 J). Note that W measures power while Wh and kWh measure energy — different quantities.