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[Sticky] How to Calculate REAL +12v Amperage

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I'd like to mention an equation that would let you find how out much amperage your PSU has on the +12v rail(s). The +12v rails are probably the most important rails on a PSU since they supply the power to the CPU and GPU. People usually overlook this part of a PSU, in fact they tend to just buy cheaper PSUs in general which will cause many issues.

If you look on the sticker, near the +12v area, you'll see the amperage of the +12v rail(s), and under that a power measurement in watts. Here is an example of the COOLER MASTER Real Power Pro 1250W PSU.


See, six +12v rails (20A/20A/28A/28A/28A/20A) with 1125W under it. This means the +12v rails combined generate 1125W of power under typical load. Since 1125W is the +12v power,  divide 1125 by 12 to get the real amperage, don't add up the number on each +12v rail. Each of those values is the max load each rail is capable of outputting.

Correct Way:
1125W/12v = 93.75A - nice value by the way

Incorrect Way:
20A + 20A + 28A + 28A + 28A + 20A = 144A

Why is that incorrect?
144A x 12v = 1728W - this is a 1250W PSU

NOTE: This does not have to be done for a PSU with a single +12v rail. Lets use the COOLER MASTER Silent Pro M 600W for example.


It tells you right there it has 40A of +12v power. If you have any doubts...

480W/12v =  40A

Not good at math? Neither am I. Use a calculator!

This topic was modified 2 years ago 2 times by strudinox
Topic starter Posted : 13/04/2009 5:23 pm
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