How to use the electricity cost calculator
Enter the appliance's power in watts, or its current in amps and your voltage. Then enter how many hours a day you use it, on how many days a week, and your electricity price per kilowatt-hour (kWh), which is on your bill. You get the energy used and the cost per hour, day, week, month and year.
Electricity cost formula
Watts = Amps × Volts
kWh = Watts × Hours ÷ 1,000
Cost = kWh × Price per kWh
A year = kWh a day × days a week × 365 ÷ 7; a month = a year ÷ 12
A kilowatt-hour is 1,000 watts used for one hour. Power companies often call it a "unit".
Worked example
A 1,500 W heater used 3 hours a day, every day, at 0.15 per kWh:
1,500 × 3 ÷ 1,000 = 4.5 kWh a day; × 365 = 1,642.5 kWh a year; × 0.15 = 246.38 a year, or about 20.53 a month.
Tips for lowering your bill
- Heating and cooling usually use the most. A degree or two on the thermostat makes a noticeable difference.
- Switch to LED bulbs: a 10 W LED gives about the same light as a 60 W incandescent bulb.
- Check your tariff: some plans charge less at night, which suits washing, drying and car charging.
Planning household spending? Use the budget calculator.
Frequently asked questions
Where do I find an appliance's wattage?
On the rating label, often on the back or underneath, or in the manual. If it only shows amps, use the amps and volts option.
Why is my real bill different?
Bills add fixed daily charges and taxes, and many have tiered or time-of-day prices. Appliances like fridges and air conditioners also cycle on and off rather than running at full power all the time.
Formulas checked 29 October 2026. How we test our calculators. Costs are estimates based on rated power. Your bill also includes fixed charges and taxes, and may use tiered or time-of-day prices.