People search for a planter by a single number far more often than by a shape, and the number usually comes from a space rather than from a catalogue: a 36 inch gap between a door and a window, a 36 inch bench to line up with, a 36 inch ceiling clearance. The problem is that a planter has three dimensions and the listing rarely says which one the headline number refers to.
So this collection is organised around the number rather than the form, and the products in it divide roughly three ways. On most, 36 inches is the length of a rectangular trough, which is the dimension that matters when you are filling a run or lining up with a bench or a railing. On several it is the overall height, which is what matters at a doorway or against a window. On one it is the diameter across the widest point, which is the footprint measurement.
Every size table on every product page gives exterior length, depth and height separately, along with the interior opening, the interior depth and the packaged weight. If the 36 inches you care about is the height, read the height column rather than the size name.