All About Fiber-Cement Siding

The calculation varies based on the type of siding. For panels, simply divide the total square footage of your exterior walls—including windows and doors, which account for waste—by the number of square feet in one piece. There isn't an easy equation for shingles, so it's best to have your supplier do the math. For clapboards, use this formula, which factors in how much of each board is exposed.