How the calculation works
kWh = W × hours ÷ 1000; cost = kWh × rate. Month = 30.4 days, year = 365.
Worked example
1500 W × 4 h at $0.15: 6 kWh/day → $0.90/day, $27.36/mo, $328.50/yr.
Common mistakes to avoid
- Using nameplate wattage when the load cycles on and off; use average draw.
- Ignoring tiered, time-of-use or demand charges on your bill.
- Forgetting standby power from always-on equipment.
Frequently asked questions
Intermittent loads?
Use average hours the load is actually on (duty cycle).
Where do I find my electricity rate?
Your utility bill lists a rate in $/kWh. For the true cost, include delivery charges and taxes, not only the supply rate.
How do I convert amps to watts?
For single-phase, watts = volts × amps × power factor. For three-phase, multiply by 1.732 as well.
Related calculators
Ohm's Law & Power CalculatorSingle-Phase & Three-Phase Power CalculatorGenerator Sizing CalculatorVoltage Drop CalculatorWire Size & Ampacity Calculator
For informational and educational purposes only. Always consult a licensed electrician and local code authority. See our Electrical & Legal Disclaimer. Found an error? Tell us.