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 out there meant to help you figure out how much power your build will use, they all share one major weakness: they are all based on the build’s maximum power requirements. They then take into account the PSU’s maximum 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 power consumption when the computer is idle. As we pointed out on page three, that’s where things tend to get really ugly, efficiency-wise.

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

 Component Type
    Description Idle (W)Load (W)Number Installed
CPUCurrent dual-core CPU
Current dual-core CPU, overclocked
Current 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 CPU
20
25
35
40
45
35
55
35
65
90
95
125
140
90-125
125-140
60-90
1
MotherboardCurrent microATX board without graphics
Current microATX board with graphics
Normal mid-range board without graphics
Normal mid-range board with graphics
High-end board
High-end board, overclocked
15
30
20
25
35
40
25
40
35
50
45
55
1
RAMCurrent DDR2 or DDR3 RAM, per 2 GB module
Current DDR2 or DDR3 RAM, per 4 GB module
Overclocked RAM per module (estimated)
2
3
4
4
5
6
1 - 4
HDDConventional hard drive28 - 10Varies
SSDCurrent solid-state drives14Varies
ODDDVD-ROM only
DVD burner
Blu-ray reader/burner
1
1
2
6
10
12
1
FanNormal CPU fan, mandatory
Silent case fan
Performance case fan
1
2
3
1 - 3
2
3
1
Varies
Varies
Add-In CardExternal sound card
TV card
Controller card
2
1
1
8
2 - 5
2
0 - 1
0 - 1
Varies
Graphics Cards
Current office-oriented card
Current mid-range gaming card
Current high-end gaming card
10 - 16
16 - 30
25 - 35
35 - 75
75 - 180
180 - 375
1
1 - 2
1 - 2
OtherCold cathode lighting, modding parts, etc.See manufacturer infoVaries


Now that we have an idea of how much power each of these components draws, calculating the overall power consumption when idling and under load is simple. Based on this information, we will define a power window in the next chapter and choose the best PSU for the job based on their individual characteristics.