Shiplap Calculator
This shiplap calculator tells you how many boards to buy for an accent wall, a whole room or an exterior wall. Enter the wall size, subtract doors and windows, choose a board profile, and get a conservative, rounded-up order with waste, fasteners and cost.
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How to Use This Shiplap Calculator
Enter the width and height of the wall in feet, the number of identical walls, and the combined area of doors and windows you will not cover. Choose the board profile, which sets the exposed face, plus the board length and direction. Slide the waste allowance to match your layout. Press Calculate to see boards to order, courses, linear feet, fasteners and cost. A table compares 8, 10, 12 and 16 ft lengths so you can pick the one with the least surplus. The diagram above redraws with your numbers.
Why This Matters
Shiplap is sold by the piece, but you cover walls by the square foot, and the gap between those two is where budgets go wrong. A 12 × 8 ft accent wall is 96 square feet. Subtract a 20 sq ft door and 76 sq ft remains. A 1×6 board only covers about 0.43 sq ft per linear foot once the lap is hidden, so that small wall needs roughly 178 linear feet before any waste. Guess from the nominal 6-inch width and you will order too few boards, make a second trip, and risk a different batch with a slightly different color.
The calculator is useful to homeowners planning a weekend feature wall, to carpenters pricing a mudroom or nursery, and to anyone cladding a garage, a shed or a covered porch. Prices vary widely by material. Primed pine, cedar and MDF commonly run from about $1 to $4 per linear foot, so a 10% ordering error on a 400 sq ft job can mean a few hundred dollars. Ordering the right length also helps. A 12 ft wall covered with 8 ft boards leaves 4 ft offcuts that can start the next course. A 13 ft wall wastes far more.
How It's Calculated
Coverage per linear ft = exposed face (in) ÷ 12
Linear ft = net area ÷ coverage
Linear ft with waste = linear ft × (1 + waste %)
Boards (area method) = ROUNDUP(linear ft with waste ÷ board length)
As a second check, the tool runs a cut plan. Horizontal boards form courses, each as long as the wall is wide. Vertical boards are each as long as the wall is tall. It counts the pieces, scales them for openings, and works out how many whole boards you need when each board yields as many full-length pieces as will fit. Offcuts are reused only for the remainder piece, and any remainder is treated as at least 1 ft long. The order is the larger of the two methods, always rounded up.
Fasteners assume framing or furring at 16 in on center, which is the common rule of thumb. Each board crosses a bearing point every 16 in, so the count is ordered linear feet × 0.75 crossings × 2 nails (1 for faces of 4 in or less), rounded up to the next 50. This is a materials estimate for interior and exterior cladding. It is not an engineering, permit or inspection approval. Exterior siding must follow the manufacturer's instructions and local code (in the US, see IRC R703), and local codes vary.
Worked Example
A 12 ft wide, 8 ft tall wall with a 20 sq ft door, 1×6 shiplap (5.125 in face), 8 ft boards, horizontal, 10% waste:
- Gross area: 12 × 8 = 96.00 sq ft. Net area: 96 − 20 = 76.00 sq ft.
- Coverage: 5.125 ÷ 12 = 0.4271 sq ft per linear ft. Linear feet: 76 ÷ 0.4271 = 177.95 ft.
- With 10% waste: 177.95 × 1.10 = 195.74 ft. Divided by 8 ft boards = 24.47, which rounds up to 25 boards.
- Cut plan: 96 in ÷ 5.125 = 19 courses of 12 ft. Scaling for the door gives 16 pieces. Each takes one full 8 ft board plus a 4 ft remainder, and two remainders fit per board, so 16 + 8 = 24 boards.
- Order = the larger of 25 and 24 = 25 boards. Surplus is 25 × 8 × 0.4271 − 76 = 9.42 sq ft.
- Fasteners: 25 × 8 × 0.75 = 150 crossings × 2 = 300 nails. At $14.50 per board the cost is $362.50.
Tips & Common Mistakes
- Use the exposed face, not the nominal size. A "1×6" is 5½ in wide and covers about 5-1/8 in once the lap is hidden. Check the package coverage and use the custom option if it differs.
- Buy everything at once. Color and milling vary between lots, so add a few spare boards to the first order.
- Acclimate the boards. Leave them in the room for 48 to 72 hours before installing so seasonal movement does not open your gaps.
- Find the framing first. Mark stud lines before nailing. Vertical boards need horizontal furring or blocking at 16 in. Stagger butt joints over studs, never in a line.
- Don't subtract tiny openings. Outlets and switches are not worth deducting. Use more waste if the wall has many cutouts, sloped ceilings or an odd shape.
- Mind moisture and fire. In bathrooms and exterior locations use boards and finishes rated for the exposure, and check local code for flame-spread requirements.
Frequently Asked Questions
How many shiplap boards do I need for a 10×10 room?
With 8 ft ceilings, four 10 ft walls are 320 sq ft. Subtracting a door and a window (about 35 sq ft) leaves 285 sq ft. With 1×6 boards at 10% waste that is about 734 linear feet, or roughly 92 eight-foot boards. Enter your own numbers above for an exact count.
How much waste should I add for shiplap?
Ten percent is the usual minimum for a simple rectangular wall. Use 15% when the wall has many windows, outlets or angles, or when you want to pick around knots and defects. Use 20–25% for diagonal or herringbone patterns.
Should shiplap run horizontal or vertical?
Horizontal is the classic look and makes a room feel wider. Vertical draws the eye up and suits low ceilings. Both use the same area, but the cut plan differs because course length and board length interact differently. Vertical also needs horizontal blocking or furring to nail into.
Do I subtract windows and doors from the wall area?
Yes, if you will not cover them. Subtract the full opening area, about 20 sq ft for a standard door and 12–20 sq ft for a typical window. The calculator still counts full-length pieces in the cut plan, so it will not under-order when openings split a course.
What is the difference between shiplap and nickel gap?
Shiplap boards have a rabbeted edge so they overlap, and the gap can be nearly closed. Nickel gap boards are usually tongue-and-groove with a deliberate gap about the thickness of a nickel. Their coverage is similar, so use the exposed face stated on the package.
How many nails or screws does shiplap need?
A common rule is two fasteners per board at each stud or furring strip, spaced 16 in on center, and one for faces of 4 in or less. This calculator rounds that count up to the next 50. Always follow the board manufacturer's fastener type, length and spacing, and local code for exterior use.