Calcaulating Wattage

[Brick1026]

When calculating the total wattage of a computer build do you just add the wattages of each individual component?

[Beef Boss]

Pretty much, but add some leeway too. So if it's 700 watts total, I'd personally get like a 900-1000 watt psu just so the power supply isn't struggling to power your system. 

[Brick1026]

4 minutes ago, aki adaki said:

Pretty much, but add some leeway too. So if it's 700 watts total, I'd personally get like a 900-1000 watt psu just so the power supply isn't struggling to power your system. 

Ok thanks I was not sure if it was that simple but its nice to know it is!

[mariushm]

Pretty much that, as a simplification. You'll want to have a power supply that can provide at least that amount of power to the components.

 

A power supply is most efficient when your components load the power supply up to around 60-80% of its maximum power. If your power supply produces less than around 40% of its rating, or it has to produce more than around 80% of its maximum rating, then its efficiency decreases.

 

For example, if your computer components use only around 200 watts, then you could use any power supply, from let's say 400w to 850w ... but a 450w model may be more efficient compared to let's say a 650w model, because its output will be at around the 50-60% load level. The 650w model may be less efficient, but being oversized, it would probably also produce less heat, so the fan it comes with may not even spin, so that 650w model may be more silent.  So you see there's tradeoffs

 

Also remember, components in a computer use 3 voltages: 12v , 5v and 3.3v. Most components these days use 12v quite a lot, but very little on 3.3v and 5v.  So it's important that the power supply can actually give that amount of power on 12v, not on all three voltages combined.

 

For example, a power supply may output 400w on 12v and 150w on 3.3v and 5v, so it can be labeled as a 550w power supply. BUT, if your components actually need 350-400w from 12v, this power supply would be borderline, for brief moments the components may take more than 400w and the power supply could shut down to protect itself and your components.

 

Also, keep in mind that components don't use the peak power all the time. For example, a video card may use up to 160 watts for example, but in a game like Fortnite which doesn't have super fancy graphics or high fps, the video card may only use 100w.

Also, the CPU may use 100w when it's at 100% load for long periods of time, but when you're gaming the CPU won't stay at 100% all the time, the load will fluctuate.

So when you're gaming, your power consumption won't be 100w (cpu) + 160w (video card) all the time

 

Also, when you add some components like let's say a DVD writer, you would have to use 10w for example, because that could be the power draw when the unit actually burns discs, spinning them at high speed and using the built in laser to burn the discs, but when the dvd drive idles or just reads discs, the power demand could be less than 1-2 watts.

 

 

[Matsozetex]

11 hours ago, aki adaki said:

Pretty much, but add some leeway too. So if it's 700 watts total, I'd personally get like a 900-1000 watt psu just so the power supply isn't struggling to power your system. 

You probably don't even have to,  most power supplies set their OPP 20% above rated wattage. And if you are EVGA a dangerous 40%.

[Gedgn]

11 hours ago, Brick1026 said:

When calculating the total wattage of a computer build do you just add the wattages of each individual component?

I'd advise you not listen to your best chosen answer. To give you a rough outlook what you do is add the cpu and gpu wattage then add an additional 100W. That is by no accurate as there are many factors to consider, just know 450-550W PSU is the max any normal user would need, even OC'ers. You see people getting 650W- 1000W PSUs because they don't know what they're doing.

10 hours ago, VegetableStu said:

https://outervision.com/power-supply-calculator

for a better estimate for your guesswork. has various 80Plus rating PSU suggestions as well

 

PS: when you see TDP and a Watt number, that's not power draw. don't use that number for power draw.

Don't link outervision it's trash and should be banned as it gives users the wrong impression. 

[Beef Boss]

1 hour ago, Gedgn said:

I'd advise you not listen to your best chosen answer. To give you a rough outlook what you do is add the cpu and gpu wattage then add an additional 100W. That is by no accurate as there are many factors to consider, just know 450-550W PSU is the max any normal user would need, even OC'ers. You see people getting 650W- 1000W PSUs because they don't know what they're doing.

Don't link outervision it's trash and should be banned as it gives users the wrong impression. 

*ahem* people with 1000k+ watt power supplies normally have more than one over clocked gpu. My answer I stated earlier was an answer I used on my comptia secondary school class, and was correct on every test I took. 

Hard drives take watts too, including USB devices and other devices in the system. Any additional sound cards, or anything. Adding 100 watts will just cover the motherboard and maybe a hard drive your answer was very inaccurate tbh. 

[seon123]

5 minutes ago, aki adaki said:

*ahem* people with 1000k+ watt power supplies normally have more than one over clocked gpu. My answer I stated earlier was an answer I used on my comptia secondary school class, and was correct on every test I took. 

Hard drives take watts too, including USB devices and other devices in the system. Any additional sound cards, or anything. Adding 100 watts will just cover the motherboard and maybe a hard drive your answer was very inaccurate tbh. 

People with ≥1000W PSUs, more often than not, have no clue, or they're miners. (I'm assuming you mean either 1kW or 1000W, and not >10^6W). A dual GPU gaming PC with overclocks will draw maybe 750W, more likely less. 

And ah, yes, a motherboard and HDD consumes 100W. Presumably all to heat. Totally. You can see all of the cooling they have in order to dissipate the heat. Right... 

How much power do you reckon a 7820X with a 1080 Ti will draw from the wall using a platinum efficiency PSU during BF1?

Spoiler

130W more than the GPU's TDP. Remove 8% for the PSU, and you have about 100W more than the GPU. Keep in mind that's for the entire system. Meaning the GPU+CPU+100W is overkill. 

https://www.anandtech.com/show/11717/the-amd-radeon-rx-vega-64-and-56-review/19

 

USB devices draw well under 1A each, and a sound card doesn't have to drive any significant amount of power. The NF-F12 has a peak draw of 0,05A or 0,6W, so 10 of those will draw 6W peak. 

[Gedgn]

44 minutes ago, aki adaki said:

*ahem* people with 1000k+ watt power supplies normally have more than one over clocked gpu. My answer I stated earlier was an answer I used on my comptia secondary school class, and was correct on every test I took. 

Hard drives take watts too, including USB devices and other devices in the system. Any additional sound cards, or anything. Adding 100 watts will just cover the motherboard and maybe a hard drive your answer was very inaccurate tbh. 

lol comptia.. most of it outdated crap they still want you to answer on tests.

 

Back on topic, you listed 700W as a total which is uncommon among normal users even power users with only one gpu. Don't know how you're calculating 700W max draw (not including disk/ usb, board), but you do not need a 1000W psu. I don't know where you're getting "1000k+ watt power supplies normally have more than one over clocked gpu" from.

 

Hard drives typically use 6W when reading/writing and 0.8 idle/sleep. Meaning you need 10 HDDs to use up 60 watts and be at load all at the same time.. I've had a 10x4TB drives, an i3, 8GB of RAM, an SSD, and 6 case fans and my server only consumes 78W at idle at the wall as measured with a kill-a-watt device, 105W at load.

 

Not sure how you're reading is, but I said a rough overall look at power estimation. In any case you need to stop giving people bad advice. Nothing you have said made any sense.

[Beef Boss]

17 hours ago, Gedgn said:

lol comptia.. most of it outdated crap they still want you to answer on tests.

 

Back on topic, you listed 750W as a total which is uncommon among normal users even power users with only one gpu. If it's 750W max draw you do not need a 1000W psu.. that doesn't even logically make any sense.

 

Hard drives typically use 6W when reading/writing and 0.8 idle/sleep, volts x amps is accurate here. Meaning you need 10 HDDs to use up 60 watts and be at load all at the same time.. I've had a 10x4TB drives, an i3, 8GB of RAM, an SSD, and 6 case fans and my server only consumes 78W at idle at the wall as measured with a kill-a-watt device, 105W at load.

 

Not sure how you're reading is, but I said a rough overall look at power estimation. In any case you need to stop giving people bad advice.

It was just for a reference. The op didn't state what the system would be, so you cannot assume it's this or that. It was supposed to be a general rule of thumb, to add some leeway. 

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Edited August 14, 2018 by SansVarnic

[LienusLateTips]

15 hours ago, VegetableStu said:

https://outervision.com/power-supply-calculator

for a better estimate for your guesswork. has various 80Plus rating PSU suggestions as well

 

PS: when you see TDP and a Watt number, that's not power draw. don't use that number for power draw.

If you half the estimate they give you you'll be closer to the actual amount required

[Stefan Payne]

17 hours ago, Brick1026 said:

When calculating the total wattage of a computer build do you just add the wattages of each individual component?

Yes, you add Graphics card and CPU TDP, the rest doesn't matter much or is in the 5-10W Area, so negligable.

 

Or you use PSU Calculator in easy mode, where you have exactly 2 Drop Down menus. Be quiet has something like that...

 

As soon as you input memory or harddrives, the result is just utter garbage and overestimated by 50% or more...

17 hours ago, aki adaki said:

Pretty much, but add some leeway too. So if it's 700 watts total, I'd personally get like a 900-1000 watt psu just so the power supply isn't struggling to power your system. 

I wouldn't because you'd overestimate what components really use by a mile or 10.

 

So let me ask this question:

A Ryzen 7/1700x

ASUS X370-F Strix

2x8 GiB DDR4-2400 Memory (well, I'm happy about the Capacity...)

2x Radeon 7970GHz/280x

 

With Prime and Heaven Benchmark

 

Does it work with a 550W or not?

Does it stay inside the 550W Margin or go over?

 

16 hours ago, VegetableStu said:

https://outervision.com/power-supply-calculator

for a better estimate for your guesswork. has various 80Plus rating PSU suggestions as well

Urgh, not again with that thing.

You know that Outervision works with some PSU companys and thus has a financial interest in overestimating?

 

Try i7-3930K (non OC) and a Radeon RX480 OC (1330MHz Core, 2000MHz Memory).

If you get something over 450W, its bullcrap.

Because in real world conditions (Prime + Heaven) we are talking about ~350W Secondary or something like that...

 

And I know that Outervision will recomend something like a rather crappy, system integrator level 700W Bronze PSU...

[Stefan Payne]

5 minutes ago, VegetableStu said:

I don't o_o when was this?

Since the beginning.

They started with Enermax and more companys used that thing.

 

And some other Companys, like be quiet, do their own Power Supply Calculator thingy....

[Brick1026]

I thought I had my best answer but now I think I have sparked a debate xD.

[SansVarnic]

@Brick1026 when calculating the power needs of your system to decide on the type of PSU you will need is quite simple.

 

As @aki adaki and @Stefan Payne both have pointed out and to add my bit; Add up all the nominal and peak usage of each major component and then add around 50-100 watts for your other components. When you have that choose the PSU that your Idle and Peak usage fit in the power curve of the psu that interests you. The key is to the find a PSU with both good efficiency and a good power curve, ideally you want to hit that 40/50% - 60/70% for best performance 40/50 being nominal and 60/70 being your max load. This way your not buying an over powered or under powered PSU. @Gedgn makes good points as well on pointing out usage and what to look for.

 

The following is found in the Cases and Power Supplies Sub-Forum;

I suggest you review this topic as it relates to this conversation; [its a long thread but the information is updated semi-regularly]

and this video [bit old but still very relevant];

This one is also a good resouurce;

and last but not least;

 

 

As @Gedgn mentioned about those that buy 1k PSU is not necessarily true, more than half those bought normally go to miners and multi-gpu systems, the other half can broken down to Water cooling, Multi-cpu systems, server style, systems with multiple HDD's and etc... and then those random ones that are purchased just like anything else are those that buy big because they can or because they dont know better (of which is a much smaller percentage than he lets on).

Now I am not saying you need a 1k watt PSU (take a look at my system stats HERE) as you most likely wont need it but just take into consideration what you need for a build vs what it is you want and most importantly what your system will need to both function normally and under load. 1k watt systems are no longer a common thing any more, I had a 900watt system a number of years ago but that was before systems became as efficient as they are now and they will continue to be come more efficient and more power hungry (depending on use case) as time goes on.

 

Hope that helps.