Electricity Cost Calculator
Calculate the running cost of any appliance by hour, day, month and year.
Please note: For planning and educational use only. Electrical installation is governed by wiring regulations and is dangerous when done incorrectly. Always have work designed, installed and inspected by a qualified electrician.
What the Electricity Cost Calculator does
Running cost is power in kilowatts multiplied by hours of use and the tariff per kilowatt-hour. Because the rating is in watts and tariffs are per kilowatt-hour, the division by 1,000 is where most mental estimates go wrong.
Formula
kW = Watts ÷ 1,000kWh per year = kW × Hours per day × Days per week × 52Cost = kWh × Rate per kWh
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Appliance | one of 11 options | Yes | — |
| Power rating | W | Yes | Check the label or nameplate. Accepts more than 0. |
| Hours used per day | number | Yes | Accepts 0 or more, up to 24. |
| Days used per week | number | Yes | Accepts 0 or more, up to 7. |
| Electricity rate per kWh | selected currency | Yes | Accepts more than 0. |
| Number of units | number | Yes | Accepts 1 or more. |
| Standby power | % | Optional | Percent of rated power drawn when idle. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Appliance and Currency.
- Enter Power rating, Hours used per day, Days used per week and Electricity rate per kWh and 1 more.
- Optionally add Standby power.
- Select Calculate.
Worked example
A 1,500 W air conditioner running 4 hours a day, every day, at $0.28/kWh.
- Watts
- 1500
- Hours
- 4
- Days
- 7
- Rate
- 0.28
1.5 kW × 1,456 hours = 2,184 kWh a year, costing $611.52 — about $50.96 a month.
Reading the result
- Cost scales with total energy — watts multiplied by hours run — not with wattage alone, so a lower-power device left on for most of the day can cost more over a month than a higher-power device used briefly.
Common mistakes
- Comparing appliances by wattage rating alone. A 2,000W heater run for one hour costs the same as a 500W heater run for four; usage pattern matters as much as the power rating.
Frequently asked questions
Where do I find an appliance wattage?
On the rating plate, usually on the back or underside. If only voltage and current are given, multiply them: 230 V × 8 A = 1,840 W.
Does standby power really matter?
Individually no, collectively yes. A device drawing 3 W constantly uses 26 kWh a year, and a typical home has dozens of them.
Method and sources
Method. Energy in kilowatt-hours from power and running time, priced at the tariff entered.
Applies to. None — you supply the tariff
Assumptions
- The appliance draws its rated power continuously while running.
Limitations
- Nameplate power is a maximum, not an average. Anything that cycles — a fridge, a heater on a thermostat — draws far less over time than its rating implies.
- Standing charges, tiered rates and time-of-use pricing are not modelled unless folded into the unit rate.
Sources
- Your own electricity bill or supplier tariff sheet — Varies by supplier. The unit rate and any standing charge, which this calculator does not ship.