Use our interactive calculator to easily convert watts to watt hours (W to Wh):
Watts to Watt Hours Conversion Calculator
Or would you instead like to convert watt hours to watts?
What Is a Watt Hour?
A watt hour (Wh) is a unit of energy equal to 1 watt (W) of power sustained for 1 hour. When talking about devices and appliances, using watt hours is a way of conveying how much electricity they use.
For example, a 10 watt LED lightbulb that runs for 1 hour uses 10 watt hours (10 Wh) of electricity. If that same lightbulb runs for 2 hours, it uses 20 watt hours (20 Wh) of electricity.
Here's the formula for converting watts to watt hours:
Formula: watt hours = watts × hours
Abbreviated: Wh = W × hrs
Why Calculate Watt Hours?
Calculating watt hours tells you how much electricity your devices and appliances use. This is useful information when trying to reduce your electricity usage and lower your monthly power bill.
Once you know which appliances are using the most energy, you can choose to use them less often or replace them with energy efficient alternatives.
For example, if you realize that a couple of your lamps still use incandescent lightbulbs, you can replace them with LED lightbulbs which use at least 75% less energy.
Also, if you want to power stuff with a battery or solar generator -- such as when going camping -- totaling up how many watt hours all your devices use is an important part in figuring out how big of a battery to buy.
How to Convert Watts to Watt Hours (W to Wh)
To convert watts to watt hours, multiply watts times hours.
Formula: watt hours = watts × hours
Abbreviated: Wh = W × hrs
For example, let's say you have a 50-watt fan, and you leave it on for 3 hours one night. Here's how to calculate its total energy consumption in watt hours:
50 W × 3 hrs = 150 Wh
So the fan's total energy consumption that night was 150 watt hours.
How to Calculate Watt Hours of an Appliance
I'll cover two ways to find out how many watt hours an appliance uses:
- Estimate watt hours from appliance specifications
- Get actual watt hours with an electricity usage monitor
Let's walk through each method.
1. Estimate Watt Hours from Appliance Specifications
Look at the appliance label or product manual for its claimed energy usage. The number will be listed in watts (W) or amps (A).
Note: The label is usually on the back or bottom of the appliance. For appliances like fridges and dryers, you may have to pull them out to find it.
For example, here are the specifications for an electric kettle I own. According to the label, it uses 1200 watts (W).
And here are the specifications for a blender I own. According to the label, the blender uses 12 amps (A).
If your appliance lists its energy usage in amps, convert amps to watts. You do that by multiplying amps times volts (W = A × V). The label should also list the voltage, which is usually 120 volts in the US and Canada. If it doesn't, look up the standard outlet voltage for your country and use that.
For my blender, the label says its voltage is 120 volts. So I do the following calculation: 12 A × 120 V = 1440 W. Turns out it uses 1440 watts.
Estimate how many hours per day you use the appliance. Convert minutes to hours if necessary by dividing minutes by 60. For instance, I estimate that use my electric kettle 6 minutes per day. 6 min ÷ 60 = 0.1 hrs.
Calculate watt hours by multiplying watts times hours (Wh = W × hrs). To estimate my kettle's energy usage, I'd do the following calculation: 1200 W × 0.1 hrs = 120 W. Thus I estimate its daily energy usage to be 120 watt hours.
2. Get Actual Watt Hours with an Electricity Usage Monitor
This is an electricity usage monitor:
You can use it to -- you guessed it -- measure how much electricity an appliance uses. Here's how:
Plug the monitor into the wall, then plug your appliance into the monitor. I used an electricity monitor called Kill A Watt, into which I plugged my electric kettle. Make sure the appliance's max current in amps is less than the monitor's current limit.
Set up your monitor, if needed. Follow the instructions in the product manual.
Wait as the monitor records the appliance's electricity usage. You decide how long to wait. For my kettle, I only use it once a day in the morning, so I decided to check it once I was done making my morning coffee.
See how much electricity the appliance used. Locate the energy usage total on your monitor, which will be displayed in watt hours (Wh) or kilowatt hours (kWh). After using my kettle, my monitor recorded 0.08 kWh.
Convert kilowatt hours (kWh) to watt hours (Wh) if necessary. To convert kWh to Wh, you multiply kWh times 1000. So I did the following: 0.08 kWh × 1000 = 80 Wh. My kettle actually uses around 80 watt hours per day.
Using an electricity usage monitor has the benefit of being exact. Recall that I estimated my kettle's electricity usage to be 120 Wh per day. In reality it's only 80 Wh -- 33% less than my estimate.
How to Calculate Watt Hours of a Battery
Watt hours tell you how much energy an appliance uses. They can also tell you how much energy a battery stores.
To calculate watt hours of a battery, multiply amp hours times volts.
Formula: watt hours = amp hours × volts
Abbreviated: Wh = Ah × V
Calculator: Amp Hours to Watt Hours Calculator
Let's say you have a 12V 50Ah car battery. Here's how to calculate its watt hours:
12 V × 50 Ah = 600 Wh
So, in this example, your car battery has a capacity of 600 watt hours.
How to Convert Watt Hours to Watts
Need to convert the other way? To convert watt hours to watts, divide watt hours by hours.
Formula: watts = watt hours ÷ hours
Abbreviated: W = Wh ÷ hrs
Let's say you use an electricity usage monitor to track the power consumption of your TV when it's turned on. One evening you watch 2 hours of TV, and afterward the monitor shows a total of 196 watt hours consumed.
Here's how to calculate how many watts your TV uses when on:
196 Wh ÷ 2 hrs = 98 W
So, in this example, your TV uses 98 watts when turned on.
Note: Most TVs consume a little power when turned off as well, so you could also repeat this test with the TV off to see how much power it uses then.
How to Convert Watts to Kilowatt Hours (W to kWh)
You won't see the words "watt hours" on your power bill. Instead, your energy consumption will be listed in kilowatt hours (kWh). 1 kilowatt hour is equal to 1000 watt hours, like how 1 kilometer is equal to 1000 meters.
To convert watts to kilowatt hours (W to kWh), first convert watts to kilowatts by dividing watts by 1000. Then multiply kilowatts times hours.
Formula: kilowatt hours = watts ÷ 1000 × hours
Abbreviated: kWh = W ÷ 1000 × hrs
Let’s say your fridge uses on average 500 watts. It runs for 24 hours a day. Here’s how to calculate how many kilowatt hours it consumes in a day:
500 W ÷ 1000 × 24 hrs = 12 kWh
So, in this example, your fridge consumes 12 kWh of electricity per day. Yep, fridges use a lot of electricity.