View Full Version : How to Determine REAL +12v Amperage on Your PSU

04-13-09, 08:01 PM
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. Lets look at my PSU for example, the COOLER MASTER Real Power Pro 650W.


See, three +12v rails with 19A on each and beneath it 540W. This means the +12v rails combined generate 540W of power at max load. Since 540W is the +12v power, divide 540 by 12 to get the real amperage, don't do 19 times 3 since that gives you 57.

Correct Way:
540W/12v = 45A - nice value by the way

Incorrect Way:
19A + 19A + 19A = 57A

Why is that incorrect?
57A x 12v = 684W - this is a 650W 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

I prefer multiple +12v rail power supplies since they are more stable (generally speaking). Here is what I recommend you look for in a PSU.

Below 400W: Above 20A on the +12v rail(s)
400W-450W: Above 20A on the +12v rail(s)
451W-500W: Above 25A on the +12v rail(s)
501W-550W: Above 30A on the +12v rail(s)
551W-600W: Above 34A on the +12v rail(s)
601W-650W: Above 40A on the +12v rail(s)
651W-700W: Above 45A on the +12v rail(s)
701W-750W: Above 50A on the +12v rail(s)
751W-800W: Above 50A on the +12v rail(s)
801W-900W: Above 60A on the +12v rail(s)
901W-1000W: Above 70A on the +12v rail(s)
1001W-1200W: Above 80A on the +12v rail(s)

Pretty much anything above 1200W has a solid +12v line, but that doesn't mean the unit is good.

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


Also check out my PSU guide.


bob saget
04-14-09, 03:21 AM
nice post!