If you will be using Dark / Black glass you may change the Thickness level to 1" inch
For Black Magic and Sands
If you will be using Black MagicGreen Sand or White Sand as your primary fireplace media you will want to change the Thickness to 1.5" this will give you the recommended 1 inch fill; to go over your burner. Note, you will want your burner holes pointing down before pouring the sand over it.
For Sand Fillers
You can change the Thickness to 1.5" this will give you the amount for a 1 inch fill. You can then double that amount for a 2 inch fill, and so on...