A linear foot is length only — two boards of equal length are equal linear feet

What this diagram shows

A diagram defining the linear foot. A reference ruler shows one linear foot equals 12 inches of length. Below it, two boards are both 8 feet long: a narrow board 2 inches wide and a wide board 12 inches wide. Both are labeled 8 linear feet, because a linear foot measures length only — the width and thickness never count, which is what separates linear feet from square feet, which count width, and board feet, which count width and thickness. The takeaway: material sold by the running foot, such as trim, fence, gutter, pipe, and railing, is priced on length, so buy it by the linear foot; buy coverage goods like drywall and flooring by the square foot instead.