I am looking for the formula which will allow me to take any GPU I desire and find out if it can fit in a pci-e 2.0 or 3.0 etc

**Any ideas where I can find this mysterious ...mythical piece of math wonder ?**

[strike]For example, I am here looking at this gtx 770 and it says

* "Memory Bandwidth (GB/sec) = 224.3" (As stated here : http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-770/specifications)

What the heck does that even mean ?? Does it run at 100% in a PCI-e 2,0 slot ? Even tho the card is PCI-e 3.0 !?

* "PCI-e v3.0: 15.75 GB/s (128 GT/s)" (As stated here : http://en.wikipedia.org/wiki/PCI_Express)

What in Einsteins name is going here ??? [/strike]

I just want to find out this formula :

*<Insert GPU here> : <insert Formula here> = <insert PCI-e here>*

**EDIT 1 :**Sorry for the misunderstanding gentlemen, after reading some replies I re-formulate my question.

How can I calculate how much PCI any given GPU consumes ? Is there a formula for that or it's grunt work, I stick it in and use software ?