Building a computer, depending on how powerful you make it, can be a pricey endeavor. Components aren’t going to be the only thing you’re paying for, though. You’ll be paying for all the electricity it uses as well. That begs the question: well, how do you determine how much you’re paying in electricity for your computer?

Thankfully, it’s actually a fairly easy equation to figure out. Be sure to follow along below!

Editor’s Note: This article was originally published in late 2013, and was now re-published in November 2016 with new and helpful information.

Determining how much your PC costs per month

The easiest way to determine how much your computer uses by the kilowatt hour (kWh) is to buy the Kill-a-Wat electricity usage monitor and plug your PC into it. Now, the average price for electricity in the United States is almost $0.13 per kWh. To determine how much your computer is using, the equation is: watts multiplied by hours used divided by 1000 times the price of electricity per kWh.

To explain that equation, your computers energy used is measured in watts. Next, we multiply how many watts were used by how long the computer is on. Then, we divide by 1000 to get our kWh usage. Finally, we multiply how many kWh were used by the price of electricity. And that’s how much you’re paying for in electricity for your PC!

ge-kwh-meterA more practical example: if your computer uses 200 watts per hour and is on 24 hours a day, the equation would look like 200 (watts) multiplied by 24 (hours in a day). That’s 4,800 watts used per day. Next, multiply 4,800 (watts) by 30 (days in a month). This gives us 144,000 watts. Now, we need to convert our watts into kilowatts. To do this, divide 144,000 (watts) by 1000. This gives us 144 kW. Finally, multiply your kilowatts — in this case 144 — by your electricity cost. Using the national average, it would be 144 multiplied by $0.13. This gives us a grand total of $18.72 per month. Assuming you use the same wattage per day, you’re paying close to $225 per year in electricity for your computer.

To get a better idea how much your electricity costs, consult your electricity bill. It’s different for everyone. For example, in Kentucky you could be paying $0.11 per kWh, but in Hawaii, you could have a steeper $0.27 per kWh.

Other ways to determine wattage used

Now, we’ve gone over the equation to determine how much wattage your computer is using, but not everyone wants to purchase a electricity usage monitor. A tool like this will give you a more precise figure, but you can also use software to determine your computer’s wattage output.

joulemeterMicrosoft makes a free software tool called Joulemeter. This gives you a breakdown of how much wattage each component is using, but also gives you a grand total at the end. Like we mentioned, Joulemeter is only going to give you an estimation — it isn’t precise by any means. That’s why Microsoft recommends you use it in conjunction with a electricity usage monitor. You can use the Kill-a-Watt tool we linked to a little while ago, but Microsoft recommends a pricier WattsUp meter.

As for the software itself, you can grab it from CNET for free, as Microsoft no longer offers it for public use because they’ve integrated into their Visual Studio software instead.

Once again, using software will only provide you with a generic estimation for wattage used. You’ll almost always need to use an electricity monitor for a precise figure.

Reducing your electricity usage

If you want, you can try and reduce your wattage used. Do you need to? Not necessarily, as there’s not going to be a whole lot you can do. Using less powerful components will help, but usually won’t be enough to make a big difference. As far as reducing the wattage components use goes, the best thing is to opt for an SSD. They use very little wattage; however, it may not be an option for some that need larger amounts of storage space for, say, video editing or gaming.

Honestly, the most practical way to reduce your wattage is to turn off the computer when you’re not using it. On the basis that your machine is using 200 watts per hour and you shut it off for 8 hours during the night, you’re reducing how much wattage you use by 1,600 watts per day. At work all day and not able to use your computer? If you keep it off for another 8 hours during that period, you’ve now doubled how much wattage you’re saving between having it shut off while at work and while sleeping at night — 3,200 watts per day.

That’s the best way to do it because, unfortunately, swapping out components isn’t going to give you as big of a difference as keeping your computer off while not using it will.

Calculating the power usage of a component

Calculating the power usage of individual components is a difficult task. Vendors don’t generally publish wattage information, and that’s likely because there’s no single “for certain” number. It all varies, and there’s so many different conditions and scenarios to take into account. For example, a processor’s wattage consumption is going to vary based on the computer being idle, working minimally, doing some hefty lifting or whether that processor is overclocked or not. So as you might imagine, the wattage consumption would be all over the map in those different scenarios.

That said, without extensive testing and research, you’re not going to get a solid figure for individual components. You can try with using Thermal Design Power (TDP) values, but it’s still not going to be an accurate figure without extensive testing. The most you can come close to is by using a power supply estimator site.

The most accurate one out there is OuterVision Power Supply Calculator, and provides an estimated power range for a wide variety of modern components. There’s two parts to it — Basic and Expert calculations. Expert calculations take into account a ton of other values, including processor and video card overclocking. The Basic option will give you quick estimates out of what you can expect from specific products. Of course, there’s other calculator options, too. Cooler Master offers one and so does Newegg.


Being aware of how much electricity you’re using can most certainly help you reduce your electricity bill by making more conscious efforts to negate your usage. As we’ve already mentioned, swapping out parts for more efficient components can help a little, but not necessarily enough to make a difference. Really, the best way to reduce your usage is to keep the computer off when you’re not using it, and that’s, really, a general rule for all household items that use electricity.

What do you do to save on your home electric bill? Let us know in the comments section below or join us over in the PCMech Forums!