Installed coverage is the dimension that creates courses
A board’s nominal name, its full measured width and its installed exposure describe different things. Overlapping edges or a tongue-and-groove profile change how much surface each added board covers. A reveal can change the course advance again. The calculator therefore asks for installed course advance directly, without guessing it from a 1 × 6 or 1 × 8 label.
For example, WindsorONE lists net widths of 5.5 and 7.25 inches for two exterior shiplap profiles and describes the selected gap separately. Those published dimensions illustrate the distinction; they are not interior-product presets here. Ask the supplier for coverage or assemble a sample at the specified reveal before entering a value.
Horizontal course count = ceiling(wall height ÷ course advance)
Vertical course count = ceiling(wall width ÷ course advance)
The last course may be narrower than a full board. It still consumes a blank of the required run length. This model does not turn a narrow final strip into a fractional stock board, nor assume that ripping it produces a second usable shiplap edge. Courses start at the bottom for horizontal work and at the left for vertical work; a centered reveal layout would move the course boundaries and can alter the opening cuts.
A window removes face area, but not every blank
Place the opening by its left and bottom edges, measured from the same wall origin. A course completely inside the opening’s cross-course extent can be divided into a left and right piece, or a lower and upper piece for vertical installation. Those shorter blanks may be cut from offcuts left by other courses.
A course that crosses only part of the opening edge is different. It needs a long blank with a notch, so the cut list retains the full run. The diagram shows the final opening cut away, while the stock schedule shows the material needed before notching. The removed notch is not reused as another profiled board; its remaining edge and dimensions would need checking.
Worked wall: 12 boards by area, 16 by the cut schedule
The example wall is 120 by 96 inches. A 48 by 48 inch opening begins 36 inches from the left and 24 inches above the floor. At 5.5 inches per course, horizontal installation takes 18 courses. Eight courses cross the opening completely, creating sixteen 36-inch side pieces. Two more only partly cross its edges and remain full-length notched blanks.
Altogether there are ten 120-inch blanks and sixteen 36-inch blanks. A 144-inch stock board loses a quarter inch at each end, leaving 143.5 usable inches. Each long blank needs its own board. Three short blanks, with two eighth-inch separating kerfs, fit in one more board; the sixteen short blanks take six boards. That gives sixteen stock boards before spare boards.
Net face area is only 64 square feet. Dividing that by the example stock’s nominal installed coverage suggests twelve boards, but those twelve cannot supply the required uninterrupted runs. This is the reason the page shows the area-only comparison beside the actual cut result rather than converting wall area directly into a shopping count.
Offcut reuse, saw width and deliberate reserve
The cut planner sorts blanks from longest to shortest and places each into the first usable stock board with enough remaining length. Offcuts are therefore reused when a later piece fits. Kerf separates successive pieces on a board; trimming is removed once at each stock-board end. The listed cut positions are measured from the start of the usable length, after the initial trim.
This is a feasible first-fit plan, not a guaranteed minimum-board solution. Grain selection, damaged ends, knots, profile orientation and appearance matching may prevent a physically long-enough offcut from being acceptable. Use the spare-board input for intentional uncut reserve, and revise the usable lengths if your stock has defects. The algorithm does not grade lumber.
Runs longer than your stock: joints, counted and staggered
When a blank is longer than the stock board after trimming, the calculator splits it into the fewest parts that fit: run length divided by usable length, rounded up. A 200-inch course on 72-inch boards becomes three parts. Odd-numbered courses start with a full usable length; even-numbered courses shorten their first part by the spare length, never more than half a board, so their joints fall somewhere else. Every joint position, measured from the wall’s left edge or bottom, is listed above the cut schedule and in the CSV, together with the smallest gap between joints in neighbouring courses.
That offset is arithmetic, not a fastening rule. If the run is an exact multiple of the usable length, there is no spare length to move and the result says the joints line up. Whether a joint must land on backing, and how the profile’s ends are cut and fastened there, comes from the product instructions and your installer. Check each listed position against the wall before cutting. Changing direction can remove joints altogether, but it also changes course count and opening interactions: read both rows of the direction comparison, including the joint count, then select the direction whose board schedule you want to inspect.
For applied vertical strips rather than overlapping wall boards, use the batten spacing planner. Framed panels and rails belong in the framed-panel tool. Those layouts do not have the same course-coverage problem as shiplap.
Shiplap measuring questions
How do I calculate how much shiplap I need?
Divide the wall dimension across the courses by installed coverage and round up to a whole course. Work out the length of each required blank, including pieces beside an opening, then place those blanks on the stock lengths you can buy. Net square feet remain useful as a comparison, but cannot show whether the last course needs ripping or whether an offcut is long enough for the next piece.
How much does 1 × 8 shiplap cover?
The name does not establish installed coverage. One documented WindsorONE exterior profile has a 7.25-inch net board width, while its chosen gap is a separate installation detail. That example is not a universal exposure for every 1 × 8 product. Use the manufacturer’s installed course advance, or measure several correctly engaged boards and divide their advance by the number of course intervals.
Should I use 6-inch or 8-inch shiplap?
Compare the installed coverage and stock lengths of the actual products. A wider course can reduce course count, but the opening position and leftover stock can change the purchase differently. Run each product’s true coverage through the calculator. The tool does not decide the appearance, fastening suitability or movement allowance from a nominal width label.
Can this calculate vertical shiplap?
Yes. The result compares both directions, and the checkbox selects which cut schedule is displayed. Horizontal courses advance up the wall from the bottom; vertical courses advance across it from the left. The run length changes when the direction changes, so a stock length that works horizontally may be too short vertically, or the reverse.
How do I include waste in a shiplap calculation?
This tool first identifies cuts, kerf, reusable offcuts and stock-end trimming. You can then add a whole number of spare boards for damage or selection. It does not add an unexplained flat percentage. A spare board is uncut reserve; a short offcut is material already left by the cut plan. They are different reasons for purchased material exceeding net wall area.
How do I calculate shiplap square feet around windows and doors?
Subtract each opening when reporting net face area, but not automatically when counting stock. A course passing fully through the opening height can split into two shorter blanks. A course only partly crossing the top or bottom edge still needs a full-length blank to notch around that edge. The diagram masks the opening, while the cut schedule preserves that full blank.
How many square feet are in a box of shiplap?
Read the product’s stated installed coverage per box, not just its nominal board count. This calculator orders individual boards, so convert the final board requirement into whole packs using the actual boards per pack. If a pack mixes lengths, this single-stock-length model cannot reproduce it; obtain a length inventory and a separate cutting plan.
Can I use this shiplap calculator for a ceiling?
It can check the rectangular course geometry if you enter the two ceiling dimensions as wall width and height, but it does not design overhead fastening, joints or support. The opening is rectangular only. Check the exact product’s ceiling suitability and installation directions, and do not treat a material cut schedule as approval of an overhead assembly.
Does it use Home Depot or Lowe’s shiplap dimensions?
No store-wide dimension is assumed. Enter the installed coverage and stock length of the specific item you intend to buy. Nominal labels, full face widths and assembled coverage can differ, including within one retailer. The example uses 5.5-inch course advance and 12-foot boards as illustrative inputs rather than claiming they describe every product.
What is the labor cost per square foot for installing shiplap?
A cut count cannot establish a local labor price. Ask the installer whether the quote includes preparation, outlet and opening detailing, trimming, finishing and removal. The result supplies wall area, course count, notched blanks and stock cuts that help define that scope. No regional installed-price average is invented by this calculator.
What the board count assumes
- One rectangular surface and at most one rectangular opening; no gables, arches, multiple windows or sloping course ends.
- Uniform installed course advance and one available stock length. Mixed-length packs require an inventory-aware plan.
- Unbroken blanks wherever the opening does not fully separate a course and the run fits the stock. Longer runs get the fewest parts, with even courses offset by up to half a usable length; backing and end treatment at each joint are not checked.
- Stock-end trimming and between-piece kerf are included; notch saw paths, fastening, paint, casing and moisture movement are not calculated.
- Geometry does not establish interior, exterior, wet-location or ceiling suitability of a product.