Enter a wall's dimensions along with board width and overlap to find the linear footage of clapboard or lap siding needed, and its cost.
How to Use the Clapboard and Lap Board Siding Calculator
Enter the wall's length and height, subtract any window or door area, then set board width and overlap. Waste percentage and price per linear foot are there for the final order and cost.
Exposure, Not Board Width, Drives the Math
Clapboard and lap siding boards run horizontally and overlap the course below, so only part of each board's width actually shows — that visible strip is called the exposure, and it's the number that determines how many courses fit up a wall, not the raw board width.
exposure = board width − overlap
board linear feet = wall area × (12 ÷ exposure)A narrower exposure packs more courses into the same wall height, which is why a smaller overlap number means less material, not more — it's a bit counterintuitive on first read of the formula. Openings are subtracted from the gross wall area before that multiplication, since siding doesn't go over glass or door slabs.