How am I supposed to know the fan size on my computer case?

there is only one for the back, how do I know if it is 120, or 80 ??How am I supposed to know the fan size on my computer case?
Measure the distance between the screw holes.How am I supposed to know the fan size on my computer case?
120's are pretty standard.





Worst case, just take the old one out, and take it to a computer store (you don't necessarily have to buy it there).





Check on www.tigerdirect.com or www.newegg.com