how many watts do i need?

[aguwah]

my build consists of:
2x sapphire raedon hd 7850 2gb
ASUS M5A97 R2.0
8 gb ram (1 stick)
1 TB 7200rpm hard drive
4 120mm case fans

i have a 535 PSU and it works fine but i am putting int the second graphics card soon and i want to know if i need a new power supply

 

[Kiora]

I would definitely go for a solid 650 watt power supply just so you have more watts then you need.

 

[Karadjgne]

you'll need a psu capable of @40A on 12vRail and 650w minimum.

http://pcpartpicker.com/part/antec-power-supply-hcg750m
http://pcpartpicker.com/part/evga-power-supply-120pg0650gr
http://pcpartpicker.com/part/seasonic-power-supply-ssr650rm

 

[JackNaylorPE]

Option 1 - Manufacturer's site

http://www.amd.com/us/products/desktop/graphics/7000/7850/Pages/radeon-7850.aspx#2

500W (or greater) power supply with one 75W 6-pin PCI Express power connector recommended7
600W power supply (or greater) with two 75W 6-pin PCI Express power connectors recommended for AMD CrossFire™ technology.

NOTE: Minimum recommended system power supply wattage is based on the specific graphics card and the typical power requirements of other system components. Your system may require more or less power. OEM and other pre-assembled PCs may have different power requirements

Option 2- Guru3D

http://www.guru3d.com/articles_pages/amd_radeon_hd_7850_and_7870_review,7.html

Here is Guru3D's power supply recommendation:

Radeon HD 7850 - On your average system the card requires you to have a 500 Watt power supply unit and 650 Watt if you go with two cards in Crossfire mode.
Radeon HD 7870 - On your average system the cards require you to have a 550 Watt power supply unit as minimum and 700 Watt if you go with two cards in Crossfire mode.

If you are going to overclock the GPU or processor, then we do recommend you purchase something with some more stamina.

Option 3 - PSU Calculator

http://extreme.outervision.com/psucalculatorlite.jsp