I am trying to replace goose egg stones around my pool area and need conversion so as to figure out how much stones I need to purchase.

From here:

Landscape supplies

1 ton is about 3/4 of a cubic yard. Cubic yards is a volume measurement. L x w x h. Yards is a length measurement and l x w is an area measurement. Keep the units straight.

4" deep x 20 feet x 10 feet; you need o convert all to a single unit first. Yards will work.
(4/36 x 20/3 x 10/3) cubic yards. Then convert cubic yards to tons by dividing by 0.75.