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Shiplap Calculator Guide
Boards for a shiplap wall, counted on coverage width — the number that isn't printed on anything.
Nominal: 1×8 — a name, not a measurement
Actual: 7.25in — what you measure across the board
Coverage: 6.375in — what it covers once the rabbet overlaps its neighbour and the gap is set
Use 7.25 and a 96in wall needs 14 rows. Use 6.375 and it needs 16. You'd be two rows short.
Coverage Width Is the Only One That Matters
Shiplap works by each board's rabbet lapping over the one below. That overlap is board you paid for and will never see, and the deliberate reveal gap eats a bit more.
The board measures 7.25 inches but contributes 6.375 to the wall — a 12% loss that compounds across every row. It's the same trap as metal roofing panels and vinyl siding, and it catches people every time because coverage width is rarely printed on the sticker.
The Gap Is the Whole Look
That shadow line between boards is what makes shiplap read as shiplap rather than as a flat wall. Traditionally it's set with a nickel — hence "the nickel gap."
Some products have it built into the profile so the boards self-space. With square-edged stock you're setting it yourself, and consistency across the whole wall is what separates a good job from an obviously handmade one. Use spacers, not your eye.
Wood Moves and the Gap Absorbs It
Real wood shrinks and swells across its width with humidity, and that movement has to go somewhere. The gap is where.
Acclimatise the boards in the room for several days before installing, or you'll fit them tight in a damp week and watch the gaps open unevenly when the heating comes on. This is the same reason flooring needs acclimatising, and it gets ignored just as often.
Find the Studs, Not the Drywall
Shiplap needs to be nailed to structure. Drywall alone will not hold it — the boards will pull loose and the whole wall will look tired within a year.
Mark every stud before you start. If the studs don't line up with where you need fasteners, add furring strips or a plywood backer, and remember that anything you add over the drywall pushes your outlets back and may need extension rings.
Start Level, Not Off the Floor
Your floor isn't level and your ceiling isn't either. Start off either one and the error compounds invisibly until it's obvious at the far end.
Snap a level line, work from that, and let the top and bottom rows take up the discrepancy — that's what trim is for. Check the last-row height before you start: a sliver at the ceiling looks wrong the same way a sliver of flooring does.
Related: wainscoting calculator, board and batten calculator, vinyl siding calculator.
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