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Picking The Right Power Supply: What You Should Know

How To Determine Your Power Requirements

A Matter Of Simple Addition

While there are many online calculators meant to help you figure out how much power your build will use, they all estimate its maximum requirement. They then take into account the PSU’s peak efficiency at a load of 50 to 55 percent and make a (generous) projection based on those numbers. The drawback is that this method does not consider consumption when the computer is idle, which we already determined is where efficiency often appears worst.

The following table is meant as a guideline, showing you how much power a certain component is likely to use under a specific load. If you know the exact figures for your components, plug them in instead and do the math.

 Component Type    Description Idle (W)Load (W)Number Installed
CPUCurrent dual-core CPUCurrent dual-core CPU, overclockedCurrent quad-core CPU (Mid-range)Current quad-core CPU (High-end)Current quad-core CPU, overclocked (High-end)Older dual-core CPU (AMD)Older dual-core CPU (Intel)Older single-core CPU202535404535553565909512514090-125125-14060-901
MotherboardCurrent microATX board without graphicsCurrent microATX board with graphicsNormal mid-range board without graphicsNormal mid-range board with graphicsHigh-end boardHigh-end board, overclocked1530202535402540355045551
RAMCurrent DDR2 or DDR3 RAM, per 2GB moduleCurrent DDR2 or DDR3 RAM, per 4GB moduleOverclocked RAM per module (estimated)2344561-4
HDDConventional hard drive28-10Varies
SSDCurrent solid-state drives14Varies
ODDDVD-ROM onlyDVD burnerBlu-ray reader/burner112610121
FanNormal CPU fan, mandatorySilent case fanPerformance case fan1231-3231VariesVaries
Add-In CardExternal sound cardTV cardController card21182-520-10-1Varies
Graphics CardsCurrent office-oriented cardCurrent mid-range gaming cardCurrent high-end gaming card10-1616-3025-3535-7575-180180-37511-41-4
OtherCold cathode lighting, modding parts, etc.See manufacturer infoVaries

Now that we have an idea of how much power each component draws, calculating the overall consumption at idle and under load is easier. Based on this information, we will define a power window in the next chapter and choose the best PSU for the job.