Circles have a different
Circles have a different equation. Remember that a radius is half the diameter of the circle. An 8 inch circle has a 4 inch radius. A 10 inch circle has a 5 inch radius.
Volume of a circle = 3.14 x radius x radius x height
So if we want an 8 inch circle that is 1/4 inch thick…
3.14 x 4.00 x 4.00 x 0.25 = 12.56 cubic inches
Again we have to convert those pesky inches to centimeters
12.56 cubic inches = 205.82 cubic centimeters
Now mulitpy by 2.5 just like with rectangles
205.82 x 2.5 = 514.55 grams Tada!
Again, if you start with centimeters it is MUCH easier
3.14 x radius x radius x height x 2.5 = grams of glass needed