How do I figure out how much pea gravel is needed to fill 8" x 60" grade retainer bands that will make a 10' circle for a 10' diameter x 15' high, 210 barrel welded tank to sit on top?

You first need to find the area of the circle.

This is done using the forumula Pi x Radius (squared).

Pi =3.141
Radius = 5 feet

Area of the circle is 3.141 x25 or 78.52 square feet.

Since the depth of the stone will only be 8", you can multiply 78.52 x 66% (8" is 66% of a foot) to get 51.83 cubic feet.

This is roughly 2 cubic yards of pea stone or 6 contractor size wheelbarrow volumes of the stone.

The math is correct but I'm confused... 60" bands but 10 ft dia tank ?