This isn't really a Mod Guide but there's no better place to put it. Here is a list of dimensions you may find useful while building your own case. Some of them I measured myself so they are accurate to about plus or minus 1mm. All dimentions are in mm. Width is the width when looking at the object head on and Depth is the width of the object when looking at it side on. Motherboards - Various Form Factors ATX PSU H: 86 W: 150 D: 140 3.5" IDE Hard Drive (I can't understand why they're called 3.5" when the width is actually closer to 4") H: 25 W: 102 D: 146 Optical Drive H: 41.3 W: 146.0 D: Can vary between about 170-220mm DDR Memory H (From MB PCB): 30 (Can be up to 48mm - more with heat spreaders) W: 134 AGP Cards W: 311.99 (Yes I know no cards of this length exist but apparently our cases are supposed to support them! For reference my GF4 Ti 4400 is 216mm wide) D: 107.96 Stuff still left to find: Maximum Width and Depth of PCI cards. I'd appreciate it if anyone else could contribute to this list. It's hardly complete. Also if there are any corrections to be made or any inaccuracies in some of the measurements then please post! UPDATES: Added the Motherboard form factor diagram. - Helping you choose your motherboard!