To find out how many gallons are in your pool, you need to know the cubic feet of your pool. One cubic foot is equal to 7.5 gallons of water. Multiply the length of your pool times the width of your pool. This is the square feet. Then multiply the depth of your pool times the square feet of your pool and this is your cubic feet. Now multiply your cubic feet times 7.5 and this will give you the amount of gallons in your pool.