In construction and home repair, square feet is a commonly used measurement. From shingles to flooring, it's important to know the entire area of a surface before you begin repairs. It's sometimes necessary to take it one step further and determine the volume of the room as well--the cubic footage. Since a cubic feet and yards are three-dimensional measures and square feet measure two dimensions, there's no simple conversion formula. But if you know the area for which you need the measurement, you can do some quick calculations to figure it out.
Know the difference between a three-dimensional measurement and a two-dimensional measurement. Square feet are calculated by only taking the flat surface area into account. That's a two-dimensional measurement. Cubic feet and yards are calculated using length, width and depth (or height). This adds the third dimension and makes it a measure of volume. The best way to think of it is as if you are figuring out how much of something it will take to fill up a box.
Determine how many square feet you are working with. The square footage of a space is essentially its area, meaning you'll need to multiply the length by the width. For example, a room that is 10 feet long and 12 feet wide would be calculated as follows:
10 feet x 12 feet = 120 square feet
Add the third dimension. Sometimes this will be as easy as measuring the height of a wall or the depth of a flowerbed, but sometimes it's a little more complicated. If you need to know cubic yards to buy items like topsoil, which are measured as such, then determine how deep you want the soil bed to be. This can be your third dimension. For example, if you wanted to fill your aforementioned room with topsoil 2 feet deep then the calculation would be:
10 feet (length) x 120 feet (width) x 2 feet (depth) =240 cubic feet
Convert the cubic feet to cubic yards. There are 27 feet in a cubic yard. Therefore to determine cubic yards, divide the cubic feet by 27. For example:
240 cubic feet/27 = 8.8 cubic yards.