Exposure is the design decision
Clapboard and lap siding are measured by exposure — the visible height of each board after the one above overlaps it. A 6-inch board with 1-inch overlap shows 5 inches of exposure. Wall area ÷ exposure = total linear feet of siding, which the calculator converts to squares for ordering.
Work top-down from the water table
Layout starts at the bottom board and works up: set the first course off the water table, snap a line at each exposure step, and the wall rises course by course. Cedar and fiber-cement both shrink across the grain — re-nail courses at the manufacturer's specified overlap and leave the expansion gaps they specify at the ends.
Sources and standards
Where these figures come from
Every formula on this page is implemented from the published reference material below. Where a value depends on a regional code, the calculator lets you override it rather than assuming one jurisdiction.
- Brick Industry Association — brick counts per square foot and mortar coverage rates.
- Vinyl Siding Institute — installation standards and product performance certification.
Figures, formulas and reference tables last verified: 19 September 2026.