This electricity cost calculator can help you understand how much running a particular appliance in your home costs you. It can be eye-opening. Perhaps it will give you some ideas for making changes in your habits that will save electricity and therefore money. But you can’t manage anything until you can measure it.

## Measuring energy usage vs power

The basic unit of power is the watt. Like the gram, it’s very small, so we mostly use the kilowatt, 1,000 watts. But we don’t want to measure power. We want to measure energy usage, which is power times time. So the most commonly used unit of energy is the kilowatt hour. Very large units include the megawatt hour or even the gigawatt hour. You might also find energy expressed in British thermal units or mechanical horsepower.

To find the annual energy consumption of a product, you need to know the product’s wattage and how many hours per day it runs.

Many appliances have their wattage stamped on a plate on the bottom or back. You may find a range of settings. A fan, for example, uses more power at its top speed than its low speed.

Some appliances list ampere usage instead. To find wattage, multiply the amperes by voltage. In the US, most appliances run on 120 volts. The larger ones run on 240 volts. You can easily enough identify them. They have a weird plug that won’t fit into a regular socket.

But why do all that work just to get a figure to plug into a simple electricity cost calculator? Just look for an online source that will estimate wattage for you. Here are two suggestions: Daftlogic has a very long and exhaustive list of products large and small. Let’s Save Electricity has a smaller chart that may be more practical.

As for the number of hours you use an appliance, you can keep a log for a while or make a rough estimate. The refrigerator presents a bit of a problem. It’s plugged in all the time, but it cycles on and off, so it isn’t always running. Eight hours makes a reasonable estimate.

## How to use the electricity cost calculator

Once you find the power consumption of an appliance, enter that figure. Notice that the default is for watts, which is very handy for light bulbs and smaller appliances. But the field has a pull-down menu where you can choose kilowatts or larger multiples. Or for that matter, British thermal units or mechanical horsepower. Use whatever unit you have found.

Next, enter the price per kilowatt hour, which you find on your electric bill. Then, enter the usage time. The calculator will compute how much power it consumes in a day (or whatever other unit you choose) and how much it costs in a year (or whatever).

Suppose you want to know whether to replace an appliance that’s still working. Find the power consumption of both the one you have and the replacement you’re considering. Use the electricity cost calculator to estimate the cost of running both of them.

Assuming the new appliance will cost less to run, you can compare the annual cost for each to find out how long it will take for the savings to pay for the new one. If it’s a short time, you can save money by upgrading. If it’s a long time, then you can save money by keeping the old one.