All Septic Riser Kits are measured by width and height. The width will be the first number and height of the second number. This system is 16" wide and 11" tall. The 16" refers to inside diameter its true total edge to edge is 18" but what matters is the inside, so this is why we refer to it as 16". The deeper the septic system is on the ground, the more comprehensive it should be beyond 2 feet. You are limited by the access size, so a 16" septic tank riser won't make the bottom hole bigger thus not making it easier to work on. It will allow a tool to go down easier and let more light to see what you are doing.
*Above is a picture drawing of the dimensions of the base for the kits*
