Shiplap Calculator — Courses, Rip Width and Board Quantity
Estimate horizontal shiplap from the installed face exposure rather than nominal board width. The result shows full course count, visible width of the final course, pieces needed across each wall, total course-run footage, and whole-board purchasing with an editable allowance.
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View all saved project estimatesWhat does the shiplap calculator calculate?
Shiplap course count equals wall height divided by each board’s installed face exposure, rounded up. This calculator also divides wall width by stock-board length for pieces per course, repeats that layout across matching walls, and adds your waste allowance before reporting whole boards and purchased linear footage.
Shiplap course and stock-board formulas
Installed face exposure determines vertical coverage because the overlap or joint hides part of each board. Horizontally, every course needs enough whole stock pieces to cross the wall. Multiplying by matching walls creates the base cut-plan quantity, and applying the allowance before rounding produces a conservative whole-board shopping count.
How to measure for an accurate estimate
- Measure each clear wall width and height after deciding how shiplap will terminate at the floor, ceiling, corners, casing, and built-ins.
- Measure or confirm the product’s installed face exposure; do not substitute nominal width or total milled width.
- Enter the stock length actually available and calculate walls separately when their dimensions, openings, or board orientation differ.
- Dry-lay several courses to decide whether the first and final boards should be ripped for balanced visible widths.
Twelve-foot-wide, eight-foot-tall shiplap wall
One wall is 12 feet wide and 8 feet tall. The selected shiplap exposes 5.5 inches per course, comes in 12-foot boards, and receives a 10% allowance for cuts, defects, and selection.
The wall needs 18 courses with a 2.5-inch visible final course. One board spans each course, so 18 boards are required before allowance and 20 boards, or 240 stock feet, are estimated for purchase.Before you purchase material
- Select material and finish approved for the room’s interior or exterior exposure, moisture conditions, substrate, and required fire performance.
- Increase allowance for many openings, staggered joints, selective grain or color matching, damaged ends, diagonal cuts, and boards with defects.
- Confirm fastening, expansion gaps, joint staggering, acclimation, and sealing requirements in the selected product’s current installation instructions.
- Order matching profile and batch where appearance matters, and save labeled spare boards for later repairs or additions.
Common questions
Should shiplap calculations use nominal width or face exposure?
Use installed face exposure, sometimes called coverage, because the joint or overlap hides part of the board’s overall width. Measuring nominal width can undercount courses. Confirm exposure from the selected profile or a dry-assembled sample before ordering material.
Why does this calculator count pieces for every course?
A wall wider than one stock board needs multiple pieces in each horizontal course. Counting only total square feet can miss those repeated end cuts and joints. This method rounds each course to whole pieces before applying allowance, producing a more conservative purchasing estimate.
Can I reuse shiplap offcuts on another course?
Often, but reuse depends on joint location, minimum piece length, stud or furring layout, end condition, pattern, defects, and manufacturer instructions. The calculator does not credit offcuts, so any safe reusable pieces become contingency material rather than reducing the initial order automatically.
How should I plan the narrow final shiplap course?
Compare the reported final visible width with the full exposure. If the last strip looks too narrow, consider ripping both the first and last courses for a balanced layout. Preserve required joint engagement, expansion gaps, fastening edges, and trim clearances.
Sources and reference standards
- National Institute of Standards and Technology — SI Units: LengthPrimary federal reference for customary and metric length definitions and relationships.
- USDA Forest Products Laboratory — Wood HandbookFederal reference for wood terminology, properties, moisture behavior, and dimensional change.
- Shiplap Direct — Premium Primed Shiplap Installation GuideManufacturer guidance for board orientation, course layout, end trimming, support, fasteners and product-specific installation.
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