American Fireglass 1/4 Inch Clear Glass

To find out how many pounds of glass you will need for your fireplace:

Multiply the average width** (inches) x the depth (inches) x your desired fill level (usually 3 or 4 inches). Divide that total by 231 and then multiply by 12.

** To find avg. width, add your front width plus the back width and then divide the total by 2.

EX: If you have a fireplace that measures 36 inches across the front opening and 24 inches across the back wall, with a 16 inch depth, and your desired fill height of 3 inches, your calculation would look like this.
36+24 / 2 = 30; 30 x 16 x 3 = 1440; 1440 / 231 = 6.23; 6.23 x 12 = 75lbs needed

Determine whether you want a raised peak in the middle (like a volcano) or if you prefer a flat surface.

For a raised peak:
Multiply the radius (inches) x the radius (inches) x 3.14. Multiply that total by the height (inches). Divide that total by 80.

For a flat surface:
Multiply the diameter (inches) x the diameter (inches) x height. Divide that total by 231. Multiply that total by .8. Finally, multiply that total by 12.