How much oven clearance do I need around my pizza stone or baking steel?

We like to have an average of about 2 inches per side for baking steel and 1.5 for pizza stones. Note these are averages, so in the case of an oven where the front and back have virtually no clearance, you need to have twice the above amounts (3 inches for pizza stones and 4 inches for baking steel) on the sides.
The main consideration before placing a pizza on baking steel or a pizza stone, is whether the air above the cooking surface is hot enough that your toppings cook at the same rate as your dough. If not, you risk getting burned crust and toppings that are barely warm on top.
This is doubly important on a grill because they get much hotter and opening and closing the grill lets out a lot of heat from the dome above the cooking surface.
Joe