How Much Power Does Your Graphics Card Need?

Actual Power Consumption And Current Requirements

Now that it’s clear what the efficiency of a power supply affects, and that all the test measurement values are taken at the socket, you can figure out the actual power consumption by subtracting the losses due to the inefficiency of the power supply. Since the graphics cards have very different load levels, the average used is 82.4% (based on manufacturer statement).

Formula for the calculation:

Actual Consumption in Watts = Measurement at Socket in Watts x efficiency of power supply

300 Watts = 364 Watts x 0.824

This step is necessary because to determine the power supply class, only the actual power consumption of the graphics card is important. The previous value, with efficiency, is only crucial for the calculation of electricity cost.

Unfortunately, now another very important factor comes into play: the current. At these high values, many older power supplies fail when a new high-end graphics card is installed. Not all 500 watts are created equal, especially when it comes to cheap power supplies. Since many components are powered on the 12 V line, the power supply also needs sufficient current (amperage, A).

Let’s take the Radeon HD 4870 as an example. AMD states “500 watt power supply” as a requirement on the packaging. According to the actual measurements, though, the graphics card doesn’t need more than 150 watts even under full load. Now we’ll calculate in 150 watts for the CPU, motherboard and drives, 300 watts should be enough. If we assume from this a 300 watt load on the 12 V line, this means 25 A is required for this rail.

Formula for the calculation:

Current Strength (Amps) = Watt : Volt25 A = 300 Watts : 12 Volts

Cheap power supply 500 watts with 17 A on the 12V line.

As you can see from the stated power rating, you can very quickly run into trouble with this 500-watt power supply, because despite the 500 W figure, it only provides 17 A on the 12 V line—at least 20 A to 25 A is necessary for a current standard PC with the HD 4870. So even if AMD sets 500 watts as a requirement, you can not assume all cheap power supplies will suffice based solely on this parameter.

With current brand name power supplies, things are different: pretty much every 500-watt brand name power supply will provide 25 A on the 12 V line. Even older brand name power supplies with fewer watts achieve the required targets.

Brand name power supply: 433 watts and 33 A on the 12 V line.

If you want to be on the safe side with your power supply, you should determine the maximum power consumption of all components, and then calculate the maximum current needed. Especially when running SLI or CrossFire, the current requirements can quickly become more important than the wattage class with high-end graphics chips (such as the GeForce Ultra 3SLI with 38.8 A at 465.6 watts).

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Actual Power Consumption Nvidia Graphic Cards2D Desktop in Watts3D Full Load in WattsCurrent in Amps (A)
GeForce GTX 280 (1024 MB)43.7204.417.0
GeForce GTX 260 (896 MB)38.7191.215.9
GeForce 9800 GX2 (2x512 MB)89.8217.518.1
GeForce 9800 GTX+ (512 MB)45.3126.110.5
GeForce 9800 GTX (512 MB)51.1131.811.0
GeForce 9600 GT (1024 MB)31.368.45.7
GeForce 9600 GT (512 MB)34.685.77.1
GeForce 8800 GTS OC (512 MB)51.9142.611.9
GeForce 8800 GTS (512 MB)51.1136.011.3
GeForce 8800 GT (1024 MB)
GeForce 8800 GT (512 MB)42.0111.29.3
GeForce 8800 ULTRA (768 MB)74.2172.214.4
GeForce 8800 GTX (768 MB)67.6158.213.2
GeForce 8800 GTS (640 MB)61.0125.210.4
GeForce 8800 GTS (320 MB)51.9112.19.3
GeForce 8600 GTS (512 MB)
GeForce 8600 GTS (256 MB)23.956.04.7
GeForce 8600 GT (256 MB)20.646.13.8
GeForce 8500 GT (256 MB)17.329.72.5
GeForce 8400 GS (256 MB)15.726.42.2
GeForce 7950 GX2 (2x 512 MB)46.1110.49.2
GeForce 7950 GT (512 MB)28.865.15.4
GeForce 7900 GTX (512 MB)33.884.07.0
GeForce 7900 GTO (512 MB)
GeForce 7900 GT (256 MB)23.948.64.1
GeForce 7900 GS (256 MB)25.549.44.1
GeForce 7800 GTX (512 MB)33.8107.99.0
GeForce 7800 GTX (256 MB)33.885.77.1
GeForce 7800 GT (256 MB)25.565.15.4
GeForce 7600 GT (256 MB)19.839.63.3
GeForce 7600 GS (256 MB)16.527.22.3
GeForce 7300 GT (256 MB)16.523.92.0
GeForce 7300 GS (128 MB)14.823.11.9
GeForce 6800 ULTRA (256 MB)47.880.86.7
GeForce 6800 GT (256 MB)42.866.75.6
GeForce 6600 GT (128 MB)21.447.03.9
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Actual Power Consumption Nvidia Graphics Cards (SLI)2D Desktop in Watts3D Full Load in WattsCurrent in Amps (A)
GeForce GTX 280 SLI (1024 MB)69.2321.426.8
GeForce GTX 260 SLI (896 MB)75.8379.031.6
GeForce 9800 GTX SLI (512 MB)95.6257.121.4
GeForce 9600 GT SLI (1024 MB)51.9125.210.4
GeForce 8800 GTS SLI (512 MB)91.5243.120.3
GeForce 8800 GT SLI (1024 MB)53.6145.012.1
GeForce 8800 GT SLI (512 MB)69.2199.416.6
GeForce 8800 ULTRA 3SLI (768 MB)221.7465.638.8
GeForce 8800 ULTRA SLI (768 MB)144.2354.329.5
GeForce 8800 GTS SLI (320 MB)94.8222.518.5
GeForce 8600 GTS SLI (256 MB)37.1104.68.7
GeForce 8600 GT SLI (256 MB)29.784.97.1
GeForce 7950 GX2 SLI (4x512 MB)87.3181.315.1
GeForce 7950 GT SLI (512 MB)42.0110.49.2
GeForce 7900 GT SLI (256 MB)34.687.37.3
GeForce 7900 GS SLI (256 MB)29.784.07.0
GeForce 7800 GTX SLI (256 MB)56.0156.613.0
GeForce 7800 GT SLI (256 MB)35.4114.59.5
GeForce 7600 GT SLI (256 MB)21.467.65.6
GeForce 7600 GS SLI (256 MB)14.845.33.8
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Actual Power Consumption AMD Graphics Card2D Desktop in Watts3D Full Load in WattsCurrent in Amps (A)
Radeon HD 4870 X2 (2x1024 MB)113.7268.622.4
Radeon HD 4870 (512 MB)68.4151.612.6
Radeon HD 4850 (512 MB)47.8109.69.1
Radeon HD 4670 (512 MB)
Radeon HD 4550 (512 MB)
Radeon HD 3870 X2 (2x512 MB)56.0202.716.9
Radeon HD 3870 (512 MB)25.592.37.7
Radeon HD 3850 (256 MB)19.872.56.0
Radeon HD 3650 (512 MB)20.651.94.3
Radeon HD 3470 (256 MB)21.429.72.5
Radeon HD 3450 (256 MB)17.323.11.9
Radeon HD 2900 XT (512 MB)64.3169.714.1
Radeon HD 2600 XT (512 MB)
Radeon HD 2600 XT (256 MB)26.456..04.7
Radeon HD 2600 Pro (256 MB)14.838.73.2
Radeon HD 2400 XT (256 MB)14.828.02.3
Radeon HD 2400 Pro (256 MB)
Radeon X1950 XTX (512 MB)31.3110.49.2
Radeon X1950 XT (256 MB)33.8123.610.3
Radeon X1950 Pro (256 MB)31.377.56.5
Radeon X1950 GT (256 MB)29.769.25.8
Radeon X1900 XT (512 MB)35.4130.210.8
Radeon X1900 XT (256 MB)30.5106.38.9
Radeon X1900 GT (256 MB)34.683.26.9
Radeon X1800 XT (512 MB)39.688.27.3
Radeon X1800 XT (256 MB)
Radeon X1800 XL (256 MB)33.857.74.8
Radeon X1800 GTO (256 MB)29.748.64.1
Radeon X1650 XT (256 MB)29.758.54.9
Radeon X1650 Pro (256 MB)
Radeon X1600 XT (256 MB)
Radeon X1600 Pro (256 MB)23.938.73.2
Radeon X1300  XT (256 MB)24.744.53.7
Radeon X1300 Pro (128 MB)19.829.72.5
Radeon X1300 (256 MB)
Radeon X800 XT (256 MB)23.964.35.4
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Actual Power Consumption AMD Graphics Card (CrossFire)2D Desktop in Watts3D Full Load in WattsCurrent in Amps (A)
Radeon HD 4870 CF (512 MB)146.7293.324.4
Radeon HD 4850 CF (512 MB)93.1216.718.1
Radeon HD 3870 X2 CF (4x512 MB)111.2416.934.7
Radeon HD 3870 3CF (3x512 MB)80.8296.624.7
Radeon HD 3870 CF (512 MB)49.4180.515.0
Radeon HD 3850 CF (256 MB)38.7144.212.0
Radeon HD 3650 CF (512 MB)39.6107.99.0
Radeon HD 2900 XT CF (512 MB)130.2359.329.9
Radeon HD 2600 XT CF (512 MB)33.8117.09.8
Radeon HD 2600 Pro  (256 MB)
Radeon X1950 XTX CF  (512 MB)67.6225.818.8
Radeon X1900 XT CF (512 MB)70.0247.220.6
Radeon X1600 XT CF (256 MB)47.886.57.2
Radeon X1600 Pro CF (256 MB)44.573.36.1
  • Inktfish
    Could you please add the Radeon 4830? :)
  • sepuko
    Took the words right out of my mouth.
  • since Core i7 920 has TDP = 130W, how can it consume 85W only?
  • 1.21 Jigawatts !!!
  • nukemaster
    This article was due. No more you need an 800 watt psu for the 4870 , core2 quad ad 1 hard drive anymore :p

    Guest11since Core i7 920 has TDP = 130W, how can it consume 85W only?The TDP is more of a design thing. Almost all of Intels initial Core2 line had a TDP of 65 watts yet many took much less power. Intel gives a worst case of that type number and does not measure every cpu.

    AMD does the same thing. They listed almost all the initial Athlon 64's at 89 watts yet many did not take that or give off that amount.

    zxv9511.21 Jigawatts !!!You act like you would need a small fusion reactor or maybe a bolt of lightning to get that?
  • neiroatopelcc
    So my system actually has a too big power supply to be effective?
    I'm running a 3,4ghz c2d with 5x500gb sata drives, a dvdrw and a 4870 on a p35 board.
    According to the article that's not going to draw the ~400W needed to get within effective range of my corsair 620 ....
  • cynewulf
    There's a mistake in the power under load for the 3870X2. It shows the same as the idle consumption. If only that were true! :D
  • Inneandar
    The TDP (thermal design power) is meant to be a guideline for the cooling solution, not the power consumption. To qualify for a cpu with a TDP of 120W, a cooler must be able to dissipate 120W. Practically, of course, this means it is an upper bound to (sensible) power consumption.

    also small note: Is it just me or is it strange to see the 260 SLI consume more than the 280 SLI. maybe in need of a beefier test scene...
  • zodiacfml
    nice collection of data. i hope many learn from this and avoid recommending too powerful supplies.
  • roofus
    better off with too much power supply than not enough. at least if you over-spec the power supply you leave some breathing room for any additional components.