How this instrument works
Shiplap is a type of wooden board, traditionally used as exterior siding and now popular as interior wall and ceiling paneling, installed in horizontal rows where each course overlaps the one below or above it through a rabbeted edge. Because each piece overlaps its neighbor, its full physical width isn't what actually shows on the finished wall — only its EXPOSED reveal, the visible portion left after the overlap is accounted for, and that's the figure this instrument's row calculation actually needs.
The math works in two independent directions: rows needed is the wall's height divided by the exposed reveal, rounded up, since that's how many horizontal courses it takes to climb from floor to ceiling. Boards per row is the wall's length divided by each piece's own length, rounded up, since that's how many individual pieces it takes to span across one row. Multiplying rows by boards-per-row gives the total count.
The exposed-reveal default of 5.5 inches is typical for a common 6 inch-wide profile installed with a 0.5 inch overlap, but the real reveal varies by the specific product — a wider or narrower piece, or a different overlap amount, changes the exposed reveal and therefore the row count meaningfully. Check your specific product's actual dimensions and adjust the Exposed reveal per board field accordingly rather than assuming the default applies to every shiplap product.
- Enter Wall/ceiling height to cover (in) — the vertical span the shiplap needs to climb.
- Enter Wall length (ft) — the horizontal span each row needs to cross.
- Enter Board length (ft) — the length of a single shiplap board, as sold.
- Enter Exposed reveal per board (in) — check your specific board's actual profile and overlap; 5.5 in is typical for a 6 in board with a 0.5 in overlap, not universal.
- Read Rows needed, Boards per row and Total boards needed beneath the inputs.
Worked example — an 8 ft wall, 20 ft long, 12 ft boards
Enter 96 into Wall/ceiling height to cover (in) — an 8 ft wall — 20 into Wall length (ft), 12 into Board length (ft), and leave Exposed reveal per board (in) at its 5.5 default, typical for a 6 in board with a 0.5 in overlap. Rows needed: ceil(96 ÷ 5.5) = ceil(17.4545) = 18 horizontal courses to reach the ceiling.
Boards per row: ceil(20 ÷ 12) = ceil(1.6667) = 2 boards to span the 20 ft wall length in each row. Total boards needed reads 36 — 18 rows times 2 boards per row, before adding any allowance for cuts at corners or wasted offcuts from staggering board end-joints between rows.
Questions
What does 'exposed reveal' mean for a shiplap board?
It's the visible portion of each board once installed and overlapped by its neighbor — not its full physical width. A piece milled 6 inches wide but installed with a 0.5 inch overlap into the one above or below it only shows 5.5 inches of face on the finished wall, and that 5.5 inch figure, not the full 6 inches, is what determines how many rows it takes to cover a given height.
How much extra should I buy for waste?
This calculator returns the exact row-times-column count with no waste allowance built in — real installations lose some material to end cuts at corners and window or door openings, and to staggering board joints between rows for a more finished look (which uses slightly more material than lining every row's joints up). A common allowance is roughly 10 percent extra beyond this calculated total.
Does this work for ceilings as well as walls?
Yes — the same row-and-column math applies; just treat the ceiling's two dimensions as height and length the same way you would a wall. Which dimension you call 'height' (rows) versus 'length' (boards per row) simply depends on which direction the boards run once installed, since shiplap on a ceiling is still laid in parallel overlapping rows just like it is on a wall.
How is this different from the site's board-and-batten calculator?
Board-and-batten uses a spacing-based batten count — vertical battens placed at a chosen interval over a base layer — an entirely different layout question from shiplap's row-times-column board geometry, where horizontal boards stack to cover height and span to cover length. The two products are installed and estimated completely differently, even though both are wood-board wall treatments.
What reveal should I use if I don't know my board's exact profile?
Check the specific product's packaging or a manufacturer's spec sheet for its stated exposed-reveal or 'coverage' figure — profiles vary meaningfully in both board width and overlap amount, so a wider board or a shallower overlap changes the reveal (and therefore the row count) from this calculator's 5.5 inch typical default. When in doubt, measure a sample board's actual overlap before ordering material for a whole wall.