If you have something 5 feet deep and 3 feet in diameter how many gallons will it take to fill this item?

First you have to calculate the volume (cubic capacity) of the container and then multiply by the number of gallons per cubic foot. Formula for calulating volume is radius-squared x pi x depth: 1.5-squared x 3.1416 x 5 = 35.343 cubic feet. There are 7.481 gallons per cubic foot, Hence, 35.343 x 7.481 = 264.40 gallons to fill the container.