Power supply: How to calculate the power I need

Power supply: How to calculate the power I need

If you have decided to build a computer , it is likely that you will have some doubts , especially if it is the first time you do it.

The most typical doubts that arise are usually about the amount of RAM memory that is needed , about the compatibility between components, and also the amount of energy or power of the power supply.

It is precisely to this last point that I will dedicate this tutorial, where you can learn in a simple way to calculate the watts you need so as not to fall short or go overboard with the acquisition of the ideal power supply or PSU. Especially important if you purchase a non- modular power supply .

Can I calculate the power manually?

The most rudimentary way is to use a pencil, paper (or do it digitally) and write down all the components that you are going to include in your PC.

In one column you write down the component and in the other the consumption in watts (w) that each of those components has. When you have them all, add the watts and you will have the result.

For example , imagine that the result is 640w. You shouldn’t buy a 650w power supply as it’s too tight. Keep in mind that

if you have the idea of updating a component in the future or if you need to add some other component to expand it, then 10w is a minimum amount that does not leave you freedom for more.

For this reason, the ideal would be to buy a somewhat larger source, such as a 700w one. That way, if you decide to expand your system,

you won’t have to buy a new power supply or use adapters/splitters to try to get more connectors out of the molexes, etc.

The problem

The problem?

If you do not have knowledge about the consumption of the components you will have it complicated. You will have to look for the information one by one.

Where can you see consumption? That is the biggest problem with this method, that if you have no idea what the consumption of each component is, you will not be able to make the list with the data.

In many online stores and product descriptions, some consumptions usually come, but it is not usual. They are not given on the manufacturer’s own website if they are not relevant data.

If you use the PC configurators such as PCComponentes, Alternate, etc., you will not need to perform this calculation, since they automatically guide and help you to choose the compatible components and adequate power.

Therefore, it is recommended to use the following procedure suitable for all users.

How to calculate power with the help of a tool

If you prefer another way to calculate the power of your future equipment and the ideal power supply, you can use an online calculator created by Geeknetic. It is very intuitive to use and quick to know what you really need. To do this, you can follow these simple steps:

  • Enter the online calculator to obtain the power of the power supply you need.
  • Now you can see the simple interface of this web app . As you can see, there are several selection menus to help you calculate the power you need.
  • You must first choose the type of motherboard . In this case, since it is a desktop PC, you should leave Desktop selected. But in case it is an ITX board or a small server, you should go for the other options.
  • The second thing is to choose, in the Processors section , between AMD / Intel, the number of sockets, in this case 1, and the CPU model you want to install. If it is a server or MP board you can choose more than 1.
  • Then you go to the RAM Memory section . There are up to 4 lines to be able to choose more modules. In principle, for a desktop PC with one is enough. For example, choose DDR4, 2 modules and 8 GB to add 16 GB (or whatever you plan to install).
  • Now it’s the turn of the Graphics Cards section . As with RAM, there are several lines, but it is common to install only one, so the first line is enough. Choose the type AMD/NVIDIA, the quantity 1, and the model.
  • Scroll down to the Storage section . In this case, it is more typical to have more than one hard drive, especially if you install an SSD. Select the quantity and type. For example, if you are going to install a primary NVMe SSD and a secondary HDD, then go to the first line, select 1, then NVMe SSD. Then in the second line choose 1 and HDD SATA 7200 RPM.
  • In Optical Units you can leave it blank or add some if you are going to include them. The current desktops do not usually have them, but if you want to install a DVD player, BluRay, recorder, etc., select what you need. There are also floppy drives, although they are increasingly in disuse.
  • PCI Express Cards and PCI Cards are two sections that are usually left blank. But if you add any type of expansion card to your computer, you must add whatever type it is: dedicated sound card, network card, TV capture card, etc.
  • Then it is the opportunity to choose the mouse and keyboard .
  • If you have a Liquid Cooling Kit / Pump you can also select it, since these make extra energy consumption. If you are only going to install CPU air cooling, then leave it blank.
  • In Fans it does not refer to the CPU / GPU, but to those that are installed in the case / tower. Select the number and diameter, for example 3x 12 cm (120mm).
  • Finally, in the Other devices section you can add some extras, especially for modding. For example if you have LED strips, RGB lighting, etc. If you have nothing, leave it blank.
  • Click the Calculate button . It will show you the result of the calculation. For example, in my case 440w estimated. But it is advisable to install a 500-600w one for what I mentioned in the previous section (for future extensions). In addition, below it also recommends some fonts that correspond to that result that you can buy.

This way you can have an idea of the source you need to buy for your PC configuration and not make a mistake. But if you have any extra devices that are not included in the Geeknetic item list, then you can do two things:

  • Add the consumption of said device manually to the final result that the web shows.
  • Add any of the existing devices as a substitute. Let me explain, imagine that you want to add a device X that is not on the list, and you know that it has an approximate consumption such as a SATA optical drive. Well, add a unit of that type and it will be added to the final result.

Choosing a good PSU or power supply

Now that you know the power required for your PSU or power supply , you can choose the brand and model of power supply.

If you also have doubts about this, you can consult our specific guide to choose the best among all the available ones, as well as to know the most important technical details.

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