How this calculator works
It divides the wall height by the exposed face width of one board to get the number of rows (rounded up), multiplies by the wall width for total linear feet, adds your waste allowance, and divides by board length to get the number of boards.
Worked example — a 12 ft wide × 8 ft tall wall with 5.25 in exposed-face boards:
96 in ÷ 5.25 in = 18.3 → 19 rows × 12 ft = 228 linear feet → + 10% waste = 251 linear feet → ÷ 8 ft boards = 32 boards.
96 in ÷ 5.25 in = 18.3 → 19 rows × 12 ft = 228 linear feet → + 10% waste = 251 linear feet → ÷ 8 ft boards = 32 boards.
Nominal vs. actual (exposed) board width
A “1×6” shiplap board is about 5.5 in wide, but the overlap (rabbet) hides roughly ¼–½ inch, so the visible face is closer to 5–5.25 inches. Always use the exposed face width, not the nominal size, or you will come up short.
Frequently asked questions
How much extra shiplap should I buy for waste?
Plan on 10% for a straight wall, and 15% if you have many outlets, windows, or angled cuts.
How do I calculate how many shiplap boards I need?
Divide wall height by the exposed board width to get rows, multiply by wall width for linear feet, add waste, then divide by the board length and round up.