Electricity Cost Calculator
Enter device wattage, daily usage hours and electricity rate to see daily, monthly and yearly costs. Add multiple devices for a total estimate. Runs locally.
Updated July 11, 2026
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Electricity Rate
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Formula Reference
Daily energy (kWh) = Watts (W) x Hours per day / 1000
Daily cost = Daily energy (kWh) x Rate ($/kWh)
Monthly cost = Daily cost x Days per month
Yearly cost = Monthly cost x 12
How to use
- 1
Enter device wattage and daily usage.
- 2
Enter your electricity rate.
- 3
See daily, monthly and yearly costs.
How it works
Why kW and kWh are different
Power (watts, W) is an instantaneous rate — how fast energy flows right now. Energy (kilowatt-hours, kWh) is power accumulated over time: a 1000 W heater running for one hour consumes 1 kWh.
Your utility bill is denominated in kWh because that is the quantity of energy delivered, not the rate at which it was drawn. This is why a hair dryer (1,500 W) used for 5 minutes costs far less than a refrigerator (150 W) running all month — the fridge accumulates vastly more kWh despite its lower wattage.
- 1 kWh = 1,000 watts sustained for 1 hour (or any equivalent product)
- Nameplate wattage is usually a max — typical draw is lower
- Standby ("vampire") draw of 1–5 W per device adds up across a whole home
How this is calculated
- Formula:
- Energy (kWh) = power (W) × time (h) ÷ 1000. Cost = kWh × electricity rate ($/kWh).
- Applies to:
- Reference rates; confirm with your local utility and tariff.
Wattage labels are typically nameplate maxima — real-world draw is often lower and varies with load. Electricity rates vary by provider, time of use (peak/off-peak), tier, and currency. Results are estimates for comparison only; not financial advice. Verify actual figures on your utility bill or with your provider.