These are the PC specs advised by developers to run at minimal and recommended settings. Those requirements are usually very approximate, but still can be used to determine the indicative hardware tier you need to play the game.
Minimum system requirements
Recommended system requirements
Graphics card: nVidia GeForce 6800GT or AMD Radeon X1950 Pro (256MB VRAM with Shader Model 3.0 or higher)
Graphics card: nVidia GeForce 9600GT or higher, AMD Radeon HD3850 or higher (512MB VRAM with Shader Model 4.0)