What this calculator does
This tool estimates how much an electrical appliance costs to run each month based on its power rating in watts, how many hours you use it per day, and the price you pay for electricity per kilowatt-hour (kWh). It works for any device — a fridge, air conditioner, space heater, gaming PC, light bulb or pool pump — and any currency, since you simply enter your own local rate.
How to use it
Enter the device wattage (often printed on a label or in the manual), the average number of hours you run it each day, your electricity rate per kWh from your utility bill, and the number of days in the month (30 by default). The calculator returns the estimated daily, monthly and yearly cost, plus the energy consumed per month in kWh.
The formula explained
Electricity is billed in kilowatt-hours. First convert watts to kilowatts by dividing by 1000. Multiply by the hours of daily use to get daily energy (kWh), then by the number of days to get monthly energy. Finally multiply by your rate:
$$\text{Cost} = \frac{\text{W}}{1000} \times \text{hours per day} \times \text{days} \times \text{rate}$$
Worked example
Suppose a 1000 W space heater runs 5 hours a day at a rate of 0.15 per kWh over 30 days. Daily energy = \(\frac{1000}{1000} \times 5 = 5\) kWh. Monthly energy = \(5 \times 30 = 150\) kWh. Monthly cost = \(150 \times 0.15 =\) 22.50. Daily cost is 0.75 and the yearly cost is about 273.75.
FAQ
Where do I find the watts? Check the device label, nameplate, power adapter, or manual. If only amps and volts are listed, watts = volts \(\times\) amps.
What if usage varies day to day? Use your average daily hours — for example, 0.5 hours if you run something 3.5 hours per week.
Does this include standby power? No. Many devices draw a small amount on standby; add those hours if you want a fuller estimate.
