Shiplap Calculator
Find how many shiplap boards you need for a wall, accounting for the overlap.
Reviewed by the ToolNestr Editorial Team — July 2026
How the shiplap calculator works
Shiplap boards are milled with a rabbeted edge so each board overlaps the one before it, creating the recognizable stepped-seam look. That overlap means a board's full width doesn't all become new wall coverage — some of it is hidden behind the overlap with the next board. The coverage that actually counts is the board's exposed width: its full width minus the overlap.
To find how many rows of boards a wall needs, divide the wall height (or width, if running the boards vertically) by that exposed coverage width, rounding up since a partial board still needs a full board cut down to fit. Multiplying the number of rows by the wall's length in the other direction gives the total linear footage of board material to buy.
Direction matters for both look and layout math. Horizontal shiplap, the traditional farmhouse style, uses the wall height as the "coverage" dimension and the wall width as the run length for each row. Vertical shiplap flips that: the wall width becomes the coverage dimension (divided into rows of boards run top to bottom) and the wall height becomes the run length. The underlying arithmetic is identical either way — only which measurement plays which role changes.
A typical overlap for common shiplap profiles is about 1/2 inch, though this varies by the specific milled profile — check your board's actual overlap rather than assuming. A 10% waste allowance covers end cuts at corners, doors, and windows, with rooms that have more openings or corners typically needing a bit more.
Nominal shiplap board widths and rabbet-joint profiles follow typical dimensions published by softwood lumber millers and trade associations such as the Southern Pine Inspection Bureau.
Measure the wall
Width and height in feet.
Check the board profile
Its width and how much it overlaps.
Order by linear footage
Total board length, plus waste.
The formula explained
Exposed coverage per board
= board width − overlap. A 7.25 in board, 0.5 in overlap: 7.25 − 0.5 = 6.75 in.
Rows needed
= ceil(height(in) ÷ exposed). A 9 ft (108 in) wall: ceil(108÷6.75) = 16 rows.
Total linear footage
= rows × wall width = 16 × 14 = 224 linear ft.
Worked example
A 20 ft × 8 ft wall, 5.5 in boards, 0.75 in overlap.
Real shiplap and MDF or engineered "faux shiplap" panels use the same coverage math but different overlap depths, so always confirm your specific product's exposed reveal before ordering. Real wood shiplap also needs an acclimation period — typically 48 to 72 hours in the room where it will be installed — to adjust to local humidity, since boards installed too dry can develop visible gaps as they later absorb moisture and expand.
Real-world context
A single accent wall is the most common shiplap project. A 10 ft by 8 ft wall using standard 7.25-inch boards with a 0.5-inch overlap has an exposed coverage of 6.75 inches per board, needing ceil(96÷6.75) = 15 rows and 15 × 10 = 150 linear feet of board, or 165 linear feet once the standard 10% waste allowance is added for end cuts.
Vertical shiplap in a bathroom, a popular treatment behind a vanity or tub, works the same math with the wall's dimensions swapped. A 6 ft wide, 4 ft tall accent using narrower 5.5-inch boards with a deeper 0.75-inch overlap gives 4.75 inches of exposed coverage, needing ceil(48÷4.75) = 11 rows and 11 × 6 = 66 linear feet, or 73 feet with waste — a small enough job that a single box of boards usually covers it.
A full living room feature wall scales up quickly. At 16 ft by 9 ft with the same 7.25-inch, 0.5-inch overlap boards, the wall needs ceil(108÷6.75) = 16 rows and 16 × 16 = 256 linear feet, or 282 feet with waste — at that quantity, buying boards by the bundle rather than individually usually works out cheaper per linear foot.
Common misconceptions
"A board's labeled width is exactly how much new wall it covers." Not with shiplap. Because each board overlaps the one below or beside it at the rabbet joint, only the exposed portion — the full width minus the overlap — actually adds new coverage. Ignoring the overlap when estimating boards leads to running short partway through the wall.
"Shiplap and tongue-and-groove board profiles are the same thing." They're milled differently. Shiplap uses a rabbet cut on each edge, leaving a visible reveal or shadow line at the seam that gives it its signature stepped look. Tongue-and-groove boards interlock with a protruding tongue fitting into a groove, producing a flush, seamless surface with no visible gap between boards.
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Frequently asked questions
How do I calculate how many shiplap boards I need?
Because shiplap boards overlap at their edges, each board only adds its exposed width to the wall, not its full width. Divide the wall height by the exposed coverage width per board (board width minus overlap) to get rows, then multiply by how many boards fit across the wall length.
What is a typical shiplap overlap?
A common overlap is about 1/2 inch, though it varies by profile — some shiplap boards have a deeper rabbet joint that overlaps more. Check your specific board's milled profile for its actual overlap before ordering.
How much waste allowance should I add for shiplap?
A common allowance is 10% for end cuts and matching board ends at wall corners or the ceiling line. Rooms with more corners, windows, or doors typically need a higher allowance since each opening creates more cut pieces.
Does shiplap run horizontally or vertically?
Both orientations are common — horizontal is the traditional farmhouse look, while vertical shiplap is popular for a more modern feel. The calculator math is the same either way: just decide which dimension is the "coverage" direction (rows) and which is the board run length.
Sources & references
This tool uses standard formulas and reference values from:
- • American Concrete Institute — ACI 318, Building Code Requirements for Structural Concrete. concrete.org
- • ICC — International Residential Code (IRC), span, footing and framing tables. codes.iccsafe.org
- • APA – The Engineered Wood Association, allowable span and load guidance.
Estimates for planning only. Span, load and code values vary by jurisdiction — verify against your local adopted code and a licensed engineer before building.