Stallion, you and Lotust crack me up. Ever try looking at a ruler? At any rate, 10mm = 1cm. ~2.54cm = 1".
As for fans, anyone with more than a couple is wasting their time and electricity. I'll tell you why. Cases have CRAPPY flow characteristics. NOTHING in the case is aerodynamic or designed to allow the smooth passage of air. As a result, people tend to employ tons of fan power to get rid of the hot air. Easiest way to do it is in two or three steps.
First, turn the fan on your CPU around. Regardless of what kind of heatsink you have, you'll end up with a hot-air-rotor around your heatsink and CPU if it blows air into the fins. Turn the fan around, and it'll pull the air in across the fins, and blow the hot air AWAY from the cpu.
Second, take a 4" case fan, or a little bigger if you want, and mount it at/on/under the top of the case. Have it blowing out. Hot air rises, and it'll help pump the heat out of your box.
Thirdly, take a holesaw, jigsaw or whatever, and cut as many holes in the sides of your case as you can. Most fans don't move as much air as they can because the airflow is restricted coming in. Make lots of holes, and there will be no problem. What about pulling in all the dust bunnies? Simple. Take a Scotchbrite pad(like the kind you can use to wash dishes) and glue/tape/fasten them over the holes. They are simple, cheap, and trap an amazing amount of dust and lint for you.
I have 6 machines all running from 558 to 930, and NONE of them are over 84 degrees. Also, none of them have any more than 2 fans in the case(not including the power supply fan). One on the CPU and on the case itself. Only exception is a dual 366 @ 616 - it has 4 fans - 2 CPUs, one case and one power supply.
Flipping the fan over will get you a min of 2 degrees C cooler right off the bat. If you want to get extreme, you can locate the power supply outside the case on top, and you'll get at least another 5 degrees C.