What this calculator does
The Device Power Consumption Cost Calculator estimates how much it costs to run an electrical appliance over time. By entering the device's power draw in watts, how many hours per day you use it, the number of days, and your electricity price per kilowatt-hour (kWh), you instantly see the total cost, the daily cost, and the total energy consumed. It works with any currency and any tariff — just enter your local price per kWh.
How to use it
Find the wattage on the device label or its power adapter (e.g. a 100 W bulb, a 1500 W heater, a 50 W TV). Enter the average hours you use it each day, the number of days you want to estimate (30 for a month, 365 for a year), and your electricity rate. The calculator handles the kilowatt conversion automatically.
The formula explained
Power on appliances is rated in watts, but electricity is billed in kilowatt-hours. One kWh is 1000 watts running for one hour. So we divide watts by 1000 to get kilowatts, multiply by hours per day and the number of days to get total kWh, then multiply by your price per kWh to get the cost.
$$\text{Cost} = \dfrac{\text{Watts}}{1000} \times \text{Hours/Day} \times \text{Days} \times \text{Price/kWh}$$The intermediate energy and cost relationships are:
$$\text{kWh} = \dfrac{\text{Watts}}{1000} \times \text{Hours/Day} \times \text{Days}$$$$\text{Cost} = \text{kWh} \times \text{Price/kWh}$$
Worked example
Suppose a 100 W device runs 8 hours a day for 30 days, and electricity costs $0.15 per kWh. Energy per day = \(\frac{100}{1000} \times 8 = 0.8\) kWh. Over 30 days that's 24 kWh. Cost = \(24 \times \$0.15 =\) $3.60, or about $0.12 per day.
FAQ
Where do I find the wattage? Check the rating label, the manual, or the power supply. If only volts and amps are listed, multiply them (\(\text{W} = \text{V} \times \text{A}\)).
What if the device cycles on and off? Appliances like fridges and heaters don't run continuously. Estimate the equivalent full-power hours per day, or use a plug-in energy meter for accuracy.
Does standby power count? Yes — many devices draw 1-10 W on standby. To include it, add the standby hours separately or use the device's average draw.
