We have had two calculations which have yielded the same answer. They are:

"One gallon contains 0.13368 cubic foot. So if your pool has a capacity of approximately 20,000 gallons, it will take 20000 X 0.13368 = 2673.6 cubic feet to fill it. Since there are 27 cubic feet in a cubic yard, that converts to 2673.6 / 27 = 99.02 cubic yards of material to fill it. To make it simple, round that off to 100 cubic yards."

Malcolm Beck's Gardenville calculation:
One cubic foot equals 7.48 gallons. 7.48 gallons divided into 20,000 gallons equals 2.673 cubic feet. 2.673 cubic feet divided by 27 equals 99.02 cubic yards
Malcolm says that holes much be punched in the deepest part of the pool, at least a one foot diameter size, and it should be dug out to hold at least ten gallons or more of one inch washed rock. Then the pools should be filled with at least one foot of one inch washed rock/gravel. Then fill the pool with any good draining top soil to within one foot of the top. Then fill the remaining space with Gardenville Lite Garden Soil.
Joe Miller of 5719 Lockhill Road (Tel: 210-696-3459) in San Antonio, Texas, did not make a drainage hole in the bottom of his pool. Instead he inserted a large (over 12 inch diameter) PVC pipe to the bottom of his pool at the deepest end through the foot of gravel on the bottom of the filled-in pool. He drilled holes in the below ground section of the pipe, especially in the gravel section, to allow excess water to filter into the pipe. He then can drain excess water from the pool during periods of heavy rainfall or can re-use irrigation water applied to the pool garden area as it accumulates on the bottom of the pool. The water is lifted from the bottom section of the PVC pipe by a submergible pump which costs about $50. Joe's pool is a 30,000 gallon pool.
The final cost of the pool filling by Gardenville will be:
"I DON'T KNOW THE DIMENSIONS OF THE POOL. SO LET'S ASSUME IT AVERAGES 3 FEET DEEP. THAT WOULD MAKE IT 900 SQUARE FEET."
"IF WE USED 12 INCHES OF ROCK ON THE BOTTOM AND 12 INCHES OF GOOD GARDEN SOIL (GARDENVILLE LIGHT MIX) ON TOP, THAT WOULD LEAVE 12 INCHES OF TOP SOIL IN THE MIDDLE."
"BUT, EACH DELIVERY COST $38.00 PLUS PRODUCT AND THE WEIGHT OF THE PRODUCT LIMITS THE GRAVEL TO 12 CUBIC YARDS PER TRIP, AND 13 CUBIC YARDS OF TOP SOIL PER TRIP, AND 16 CUBIC YARDS OF THE LIGHT MIX PER TRIP."
"WE WOULD END UP WITH 3 TRIPS EACH FOR THE GRAVEL AND TOP SOIL AND BE SLIGHTLY OVERLOADED IF WE ONLY MADE 2 TRIPS ON THE LIGHT MIX."
"SINCE THE POOL IS RIGHT AT 100 CUBIC YARDS, IT WOULD TAKE 33.3 CUBIC YARDS OF EACH."

"FOR THE BENEFIT OF ECONOMICS, LET'S DO IT IN ONLY 7 TRIPS INSTEAD OF 8 TRIPS, AND ALSO GO HEAVIER ON THE TOP SOIL — THE LEAST EXPENSIVE OF THE THREE INGREDIENTS. WE CAN DO THAT WITHOUT REALLY HURTING THE QUALITY OF THE GARDEN.
LET'S USE: 24 YARDS OF ROCK AT $19.00 == $456.00
46 YARDS TOP SOIL AT $12.00 == $552.00
30 YARDS LIGHT GARDEN MIX AT $23.75 = $712.50
7 DELIVERIES AT $38.00 == $266.00

TOTAL COST $1986.50

WITHOUT THE ADJUSTMENTS THE COST IS $2127.17 OR $140.67 SAVINGS

Since the upkeep on a pool is approximately $200 per month — labor not include — a person could pay for the conversion in less than a year.