SUGGESTION: Use less expensive glass on the bottom (i.e. clear, bronze, gray) to save on your overall cost.
(π • r² • h) is the volume formula for a round fire pit
(π • r² • h) ÷ 22.5 in.³
22.5 = cubic inches per pound of FireCrystals
Weight is 10.5 pounds per gallon
Calculations are amounts we suggest for a 3 inch thickness in the fireplace to achieve the proper thermal dynamic efficiency, which we have proven over the last seven years of test burning.