HANDY MEASUREMENTS FOR GARDENERS 3 teaspoons equal 1 tablespoon 2 tablespoons equal 1 ounce 8 ounces equal 1 cup Square feet equals length x width Cubic feet equals length x width x height 1 cubic foot is 12 inches by 12 inches by 12 inches Determining how much soil or compost you need Most soil and compost comes in bags that are measured in cubic feet. So how do you determine how much soil is needed for an area measured in square feet? First calculate the number of square feet: length x width For example, if your area is 3 feet long and 4 feet wide, the number of square feet equals 12. Next determine the thickness or height of the material. In other words, do you want 3 inches of top soil to cover the area? If so, the height of the material is 3. Now convert the height of the material into height in feet using this formula: height divided by 12 (inches) For example, if you want 3 inches of material to cover your area, divide 3 by 12 to arrive at .25 feet. Now you have the necessary information to determine how many cubic feet you need. Just multiply square feet x height in feet and you'll have your answer! In our example, 12 square feet x .25 equals 3, so you'll need 3 cubic feet.