Splashing around in the swimming pool may be a great way for your family to spend a summer afternoon, but it can also be destructive to the landscaping around the pool. Water that's expelled from the pool from splashing or people just getting in and out of the pool, along with the increased traffic, can turn the area into a horrible looking mud pit. To combat some of these issues, you can install a ring of gravel around the pool. Gravel will not show signs of water damage and can even be used to cover a sloped drain, to move excess water away from the pool area. The amount of gravel you will need around the pool depends on the pool shape and desired gravel depth.
Things You'll Need
 Measuring tape
 Pen and paper
 Calculator
Circular Gravel Area

Measure the distance from the center of the pool to the outside edge of the gravel area. Record this measurement as the gravel radius. Measure the distance from the center of the pool to the edge of the pool. Record this distance as the pool radius.

Measure the depth of the gravel trench around the pool. If the trench is sloped, or just doesn't have an even height, make ten or more height measurements at random locations and average the results.

Multiply the gravel radius by itself, then multiply the result by 3.14, and finally multiply everything by your height measurement. Make the same calculation using the pool radius instead of the gravel radius.

Subtract the second result, where you used the pool radius, from the first result, where you used the gravel radius. This is the volume of just the gravel area you need to fill in.
Elliptical (Oval) Gravel Area

Measure the distance from the middle of the pool to the outside edge of the gravel area at one of the two furthest points of the oval. Record this as gravel measurement "A." Make the same measurement but just to the edge of the pool, and record it as pool measurement "A."

Measure the distance from the middle of the pool to the outside edge of the gravel area, but this time at one of the two closest points of the oval. Record this measurement as gravel measurement "B." Make the same measurement to the edge of the pool, and record it as pool measurement "B."

Determine the height of the gravel area by either measuring it once, for a level area, or by making ten or more measurements and averaging the results.

Multiply gravel measurement "A" and "B" together, then multiply the result by 3.14, and finally multiply that result by the height measurement. Make the same calculations using the pool measurements.

Subtract the second result, which you got using the pool measurements, from the first result, which you got using the gravel measurements. This will give you just the volume of the gravel area.
Rectangular Gravel Area

Measure the length and width of the gravel area and the length and width of the pool inside the gravel area.

Measure the height of the gravel area. For sloped surfaces, just take ten or more measurements and average the results.

Multiply the length, width and height of the gravel area together. Multiple the length and width of the pool together, and then multiply that by the height of the gravel area.

Subtract the second result, which used the pool measurements, from the first result, which used the gravel area measurements. This will give you just the volume of the gravel.
Tips & Warnings
 Make your measurements in inches, not feet, and round to the nearest inch. This will help keep the math simple.
 Divide the result, which should be in cubic inches, by 1728 to get the number of cubic feet.
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References
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