The Corsair Obsidian 800D has a the E-ATX form factor. Extended ATX is a slightly deeper version of the ATX standard which is designed to provide all the advantages of ATX but with slightly more room. Using the E-ATX standard, the case can house motherboards and power supplies with form factors ATX, E-ATX and Micro-ATX. The dimensions of the case itself (LxWxH) are 609mm x 229mm x 609mm.

The Corsair Obsidian 800D has seven expansion slots, so there is plenty of room for extra components, which may be a deciding factor when planning on the longevity and build type of a PC system. The case has five 5.25" drive bays, which is more than enough to house various drives, particularly optical drives. With six 3.5" drive bays there is also plenty of extra HDD space as well. Installing a solid-state drive on this case would require a 3.5" adapter. Installation of hard drives into these drive bays is made all the more easier by screwless rails that allow tool-less mounting.

Made primarily of Steel, the Corsair Obsidian 800D is built to be strong and well-ventilated. Steel cases are generally fairly cheap and sturdy, but also tend to be quite heavy. Whatever your case's material, it is important to keep a consistent airflow so that heat doesn't build up inside. It is therefore advised that you make use of the available built-in case fans and fan installation sections.