If you’re taking an active interest in your household energy efficiency, you may find yourself thinking more about the wattages of the appliances you own or purchase, such as refrigerators, dishwashers, even TVs. Knowing the wattages of your appliances is a helpful way to quantify your overall energy consumption, giving you a better idea of where all that energy is going when you get your bill each month. 

There are a few simple calculations you’ll need to learn to get started, but once you know them, you can estimate the cost of just about every appliance or device in your home.

How Many Watts is a Kilowatt?

The basic unit we use to measure electricity is the watt, named after Scottish inventor James Watt, whose steam engine helped fuel the Industrial Revolution. In most cases, when you look up an appliance’s wattage in an owner’s manual or on an appliance label, it will be expressed in watts with a number followed by a capital “W.”

Your electrical utility may be more likely to communicate in terms of kilowatts (kW) than watts. A kilowatt is equal to 1,000 watts, and is commonly used in calculating monthly electric bills. The wattage formula for converting between these units depends on whether you’re calculating watts (W) to kilowatts (kW) or vice versa:

Watts to kilowatts:

W / 1,000 = kW

Kilowatts to watts:

kW x 1,000 = W

How kWh is Calculated 

On your electric bill, you’ll see that you’re billed based on how many kilowatt-hours (kWh) you use. What is a kilowatt-hour? A kilowatt-hour is equal to the total amount of electricity that is consumed when one kilowatt (1,000 watts) of electricity is consumed for one hour. 

Calculating kWh can help you figure out how much it will cost to run an appliance, as long as you know the appliance’s wattage and how long the appliance will be running. First, calculate the kilowatt-hours by multiplying the wattage by the number of hours, and dividing the product by 1,000:

(W x hours) / 1,000 = kWh

Once you calculate the kilowatt-hours, you can check your latest electric bill to find your kilowatt-hour rate. Then multiply the answer to your previous calculation by the kilowatt-hour rate to estimate the cost of running the appliance.

Here’s an example – let’s say you have an electric clothes dryer that runs on 2,500 watts, and a full cycle takes an hour and a half to complete. Let’s also assume the price of electricity is 13 cents per kWh.

First, calculate the kWh per cycle:

(2,500 W x 1.5 hours) / 1,000 = 3.75 kWh

Next, calculate your electricity costs:

3.75 kWh x .13 = 0.4875

In this case, it costs about 49 cents to run this dryer for a full cycle.

Calculating the Wattage of an Appliance ​​

In many cases, you can find the wattage of an appliance or device without doing any calculations. You may find the wattage listed in the owner’s manual, and if not, you may find it printed on a label or stamped into a metal plate on the appliance itself.

If you don’t see the wattage listed anywhere, look for the amperage. This is measured in amperes, which you may see abbreviated as “A” or “amp.” You can calculate wattage by multiplying the amperage by the voltage (v). The voltage for most standard appliances in the United States is 120 (a standard electrical outlet is a 120v outlet). Larger appliances like dryers and electric ovens may use 240v, and will use a different type of plug and outlet.

How Accurate Are These Calculations?

Some appliances and electronics are very consistent in how they consume electricity, and others are not. Sometimes, this is by design – for example, a refrigerator’s compressor cycles on and off only when needed to maintain a specific temperature. This helps save as much energy as possible while also accommodating variations in how full the refrigerator is, how frequently the door is opened, etc. 

Any appliance or device that has multiple intensity or heat settings – ovens, hairdryers, fans, dimmable lights, etc. – will also consume varying amounts of electricity. So while wattage-based calculations can give us a good idea of how much electricity our appliances are consuming, they don’t tell the whole story.

But you can get much more exact information if you really want it. A low-priced option is to invest in a simple electricity monitor, which usually retails for under $50. These devices can give you a real-time reading of electricity consumption and are simple to use, but they have some limitations. Most of these monitors are only designed for use with 120v plug-in appliances, so you won’t be able to use them on larger appliances or hardwired fixtures. And you can only use the monitor on one appliance at a time.

For more sophisticated data, you can invest in a smart home energy monitoring system. These devices connect to your electrical panel and transmit energy use information electronically, usually through a smartphone app. These systems are designed to detect unique electrical signatures of individual appliances and devices, giving you around-the-clock, real-time data on which appliances are running and how much electricity they’re consuming.

But even the old school, back-of-the-envelope approach can be a good way to get a rough idea of how much electricity appliances use and how much they’ll cost you. It’s all part of being mindful about energy use to reduce waste and save money. If you're curious about your household's energy consumption, take a look at our article on how much energy a typical house uses.