Linear × width = area
A linear foot is 12 inches of length, whatever the width. Multiply <strong>linear feet × width in inches ÷ 12</strong> and you have square feet — the conversion for fence boards, decking, counter edging, baseboards and any product sold by length with a fixed width.
Why suppliers sell by the linear foot
Width varies by product, so length is the only comparable measure — a 6-inch fence board and a 12-inch one are both priced per foot of length. The calculator is bidirectional in practice: buyers convert linear feet to coverage, and coverage back to linear feet when the budget needs trimming.