A square foot is a unit of measurement of area. A piece of material measuring 12 inches by 12 inches is one square foot. To compute the number of square feet in a piece of wire mesh you multiply its width in feet times its length in feet. For example, a piece of wire mesh 4 feet wide and 3 feet long would be 12 square feet.

A linear foot (sometimes called a running foot) just measures length. One linear foot equals one foot long, no matter how wide the material is. So if something is 3 feet wide and 15 feet long, it's 15 linear feet. That same piece is 45 square feet when you factor in the width (3 × 15).