What this calculator does
The Appliance Energy Cost Calculator estimates how much electricity an appliance uses and what it costs you over a day, a month, and a full year. Enter the device's power rating in watts, how many hours you run it, how many days a week you use it, and your electricity price per kilowatt-hour (kWh) — the same unit shown on your power bill. The calculator works with any currency, since the answer comes out in whatever currency your rate is in.
How to use it
Find the wattage on the appliance label or its manual (e.g. a 1500 W heater). Estimate the hours you use it on a typical day and how many days per week. Look up your rate per kWh on your latest utility statement. The tool converts watts to kilowatts, multiplies by usage, and scales to longer periods.
The formula explained
Energy in kWh equals power in kilowatts times hours: $$\text{kWh} = \left(\text{watts} \div 1000\right) \times \text{hours}$$. To get an average per calendar day, we multiply by days-per-week \(\div\) 7. Cost per day is that energy times your rate. Monthly cost uses an average of \(30.4375\) days and yearly cost uses \(365.25\) days, so the figures stay consistent across a full year.
Worked example
A 100 W device run 5 hours a day, every day (7 days/week), at $0.15/kWh: daily energy $$= (100/1000) \times 5 = 0.5 \text{ kWh}.$$ Daily cost $$= 0.5 \times 0.15 = \$0.075.$$ Yearly cost $$= 0.075 \times 365.25 \approx \$27.39,$$ and monthly \(\approx \$2.28\).
FAQ
Where do I find the wattage? It is on the appliance's rating label, often near the power cord, or in the manual. If only amps and volts are listed, \(\text{watts} = \text{amps} \times \text{volts}\).
What if I don't use it every day? Set "Days per week used" to match — e.g. 3 for a weekend-only appliance. The daily and monthly figures become averages.
Why 365.25 and 30.4375? These account for leap years and the fact that months have different lengths, giving a more accurate annual estimate.
