how can i know if it can fit it

Solution
Physical dimensions of GPU: 4.6 x 6.9 x 1.4 in

If you have more than 7in of clearance from the back of your case to where ever the next obstacle would be, say HD slots, then it will fit. At least length wise. As long as there are no fans on the side panel directly over the PCI-E slot for the GPU, then you are in good shape.

i have a normal black box.. not expensive one
 
Physical dimensions of GPU: 4.6 x 6.9 x 1.4 in

If you have more than 7in of clearance from the back of your case to where ever the next obstacle would be, say HD slots, then it will fit. At least length wise. As long as there are no fans on the side panel directly over the PCI-E slot for the GPU, then you are in good shape.
 
Solution
^^^ That's why I suggested actually measuring the distances in the case. We can see the card's physical dimensions, next step is to bust out the tape measure and, measure.
 


simple


open your case and measure the space

WC8mooJ.jpg



this will give you max length of the gpu you can fit



also make sure your power supply is good enough to power the card

pre-builts usually have crap power supplies