The short answer
Electricity cost equals electrical input watts ÷ 1,000 × hours of use × your price per kWh. For several comparable use days, multiply by that day count. The formula assumes the entered power is drawn throughout the time; accumulated kWh is a better input when the draw varies or cycles.
The calculation in one line
Electricity cost = input watts ÷ 1,000 × hours of use × price per kWh.
Use the electrical power the appliance draws, the time over which that draw applies, and your electricity unit rate. Reading Municipal Light Department explains this power, time and energy relationship in its electricity-use guidance.
For several similar days, multiply the daily result by the number of use days. The electricity cost calculator accepts W or kW and hours or minutes, so you can keep the units used in your source.
Turn minutes into hours
Suppose an illustrative appliance draws 1,200 W continuously for 25 minutes:
| Step | Calculation |
|---|---|
| Convert input power | 1,200 ÷ 1,000 = 1.2 kW |
| Convert time | 25 ÷ 60 hours |
| Calculate energy | 1.2 × 25 ÷ 60 = 0.5 kWh |
| Apply an example tariff | 0.5 × £0.28 = £0.14 |
| Repeat on 20 use days | 10 kWh, costing £2.80 |
The tariff and appliance figures are illustrative. Enter 0.28 for 28 pence per kWh, or 0.20 for 20 cents per kWh in the matching dollar or euro currency. Read pence and cents conversion if your bill uses smaller units.
Choose the correct watts
Electrical input is the number needed for this estimate. Cooling capacity, microwave cooking output and a water-removal capacity describe different things. A maximum power rating also does not establish an appliance’s average draw throughout a session.
For equipment that changes power or switches on and off, either use a representative average over the entered time or choose measured accumulated kWh. Do not enter both a reduced average and an additional assumed cycling reduction.
Use measured energy when the draw varies
For complete-day measurements, choose the calculator’s measured mode. If an appliance-only sample records 4.8 kWh over three complete days, its sampled daily average is 1.6 kWh. Projecting that average onto 20 comparable use days gives 32 kWh, costing £8.96 at the illustrative £0.28 tariff.
The measurement already includes the operation captured during those days. A single active-hour reading is unsuitable for the complete-day field. Read how to record a useful sample before extrapolating.
Decide what period the result represents
Enter actual use days for a month, season or other period. A heater used during winter needs a different schedule from a continuously operating fridge. Keep a note of the mode, setting and conditions that your estimate assumes.
This calculation covers electricity at a constant entered unit rate. Fixed charges are excluded. If use crosses different tariff periods, calculate the energy in each period separately and add the costs, following the time-of-use guide.