The Asus website and your owner's manual should tell you what you need. The Crosshair Formula III can use up to 16 GB. of RAM which means 4 x 4 Gb. DIMMs per the link below. You will want to buy a MATCHED TESTED SET of 4 x 4 GB. specifically for your Mobo/CPU - to be sure the DIMMs will all work together properly. You may also need to update your mobo BIOS.