Calculate how thick the sand will be. The layer of sand is usually 1 or 2 inches thick; it should be thick enough to work with and to smooth over any eccentricities.
Divide the pool (mentally) into its subcomponent shapes. Many pools are simply a rectangle or circle, but others have more complex geometries best described as a combination of rectangles, circles, and triangles.
Calculate the area of each shape. The area of a triangle is base multiplied by height. The area of a triangle is 1/2 its base multiplied by its height (where height is the length of the line running perpendicularly from its base to its vertex). The area of a circle is pi (approximately equal to 3.14) multiplied by the square of its radius.
Add the individual component areas together to obtain the total area of the pool.
Convert the desired height into a base unit that is in common with the calculated area. If you calculated the area in square feet, divide the number of inches by 12.
Multiply the desired height of the sand layer by the pool's area to get the total volume of required sand.