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What is a “Watt” Anyway?

Your Sense app speaks in the language of watts. But what is a watt? How many watts are too many? Why do we use watts for the Sense app? Why do we use them even though electric bills show “kilowatt-hours” instead of watts?

Your Sense app speaks in the language of watts, but not everybody really knows what a watt is. Luckily, Sense is here to shed some light on the situation, so you’ll know the answer to burning questions like “how many watts is ‘too many watts’?”, “what does ‘kW’ even mean?” and “what are all of these ‘kilowatt-hour’ things on my electric bill?” Knowing what a watt is is the first step to lowering your electric bill, so lets dive right in!

Watts

A watt (W) is a unit that measures electricity. Specifically, it measures the rate at which electricity is flowing. Different devices need different rates of energy to run, which is why a coffeemaker might use 900W, but a ceiling fan would use 65W. You can think of watts as the electrical equivalent of horsepower. (Fun fact: 1 horsepower=745W)

Orders of Magnitude

On your Sense app, your appliances’ power usage is usually measured in watts (W), but your house’s total power usage is often measured in kilowatts (kW). A single kilowatt is equal to 1000 watts. So for example, if your house is using 2kW, it’s consuming 2000 watts. Kilowatts are just an easier way to measure large amounts of electricity.

So What is Too Many Watts?

Well, the answer is different for everybody, but here are a few numbers that will help to establish some kind of scale:

Watt visualization

Data from: Source 1,  Source 2, Source 3, Source 4, Source 5

What About “Kilowatt Hours”?

Many electric bills will charge by the “kilowatt hour,” or “kWh.” One kilowatt hour is equal to the amount of energy consumed if work is done at an average rate of one thousand watts (one kilowatt) for one hour.

We know, we know, it’s such an awkward term! Think of it as similar to how “light-years” aren’t actually a measure of time, they’re a measure of distance. Even though “kilowatt-hour” sounds like it should measure a rate because it has the word “hour” in it, it actually measures a quantity of energy, while watts are the real measure of rate.

When Do You Use Kilowatt Hours and When Do You Use Watts?

Electric-bill

Kilowatt hours are used for electric bills because they can represent the amount of electricity used historically. In contrast, watts cannot be used in energy bills because they are the rate at which you are using electricity at some given time. Sense shows you watts because in order to give you real-time home energy monitoring, we have to use a unit of measurement that applies to real-time. Sense also sometimes uses average watts over some time period – this just allows you to directly compare your usage right now to your average over the time period.

Example Time!

Think of watts as a measure of speed, (miles-per-hour), and of kilowatt-hours as a measure of distance traveled, (miles). When you are driving a car, you can say “I am currently traveling 60 miles-per-hour.” However, were you to add up the amount of miles you drove in the last month, you would not say “I drove 60 miles-per-hour this month” to represent the total amount of miles you drove. You would say “I drove 800 miles this month.”

To translate this into the real world: when your microwave is on, it is using somewhere between 750 watts and 1100 watts, depending on the type of microwave. However, on the average monthly electric bill, your microwave might contribute 10 kilowatt-hours, and it wouldn’t make any sense to try to swap those two units.

How Can I Calculate Kilowatt Hours?

You can calculate kilowatt hours yourself by multiplying the wattage of a device by the number of hours it was used. Or, skip the math and use this converter.

What Are “A Lot of Kilowatt Hours”?

Here are the estimated kWh usages of the devices mentioned previously:

Kilowatt visualization

Data from: Source 1, Source 2,

And here are some total home kWh/month stats from across the country:

Kilowatt US Map

Data from: Source

You may notice that these same eight devices measure up differently in watts versus kilowatt hours. For example, a microwave uses significantly more watts than the plasma TV, but significantly less kilowatt hours. This is because kilowatt hours are time-dependent. While a microwave uses more watts, it only runs for a couple of minutes maximum each time it runs, so it has a low kWh. Meanwhile, a TV uses less watts, but in most houses will run for hours at a time, so it has a high kWh.

You can see this difference in your Sense app. For example, while you may see a noticeable bubble pop up in your “now” page when your aquarium heat is turned on, the percentage of power it takes up over time (as seen in the trends chart) is actually quite small.

Hopefully this clears up the mystery of the watt!

Happy energy saving,

-The Sense Team