How to use the shiplap calculator
- Enter the wall length and wall height in feet. If you are covering several walls, add their lengths together and use one height.
- Subtract doors and windows by entering their total area in square feet.
- Measure the visible face width of one board once it is installed, and enter the board length. The default of 5.5 inches is an example.
- Set a waste allowance and read the number of boards to buy, plus a row-by-row check.
Formula
Area to cover = wall length x wall height - openings
Area with extra = area x (1 + waste % / 100)
Coverage of one board = visible width (in) / 12 x board length (ft)
Boards = area with extra / coverage of one board, rounded up
The row check divides the wall height by the visible width to get rows, and the wall length by the board length to get boards per row, assuming offcuts are not reused.
A 20 by 10 foot accent wall
The wall has 200 square feet and no openings. With 10 percent extra the area is 220 square feet. A board with a 5.5 inch visible face and a length of 8 feet covers 5.5 / 12 x 8 = 3.667 square feet, so 220 / 3.667 = 60 boards.
The row check gives 10 ft x 12 / 5.5 = 21.8, which is 22 rows, and 20 ft / 8 ft = 2.5, which is 3 boards per row, or 66 boards if every row is cut from new boards. If the wall has 40 square feet of windows and doors, the area becomes 160 square feet, 176 with extra, and 48 boards. With a 6 inch face the same wall needs 55 boards.
Use the visible width, not the nominal width
Shiplap boards overlap or lock together along their edges, so the part you see is narrower than the board. A board sold by a nominal width shows less than that width once installed. Measure the exposed face of a sample board, or read the specification, and enter that. Using the wrong width is the most common cause of buying too few or too many boards.
Run the boards across the wall and plan the last row at the top or the bottom, where it can be ripped to fit. A last row cut very narrow looks awkward, so some people adjust the first row to balance it.
Area method and row method
The area method assumes you can use offcuts, so it is the lower estimate. The row method assumes each row starts with a new board and discards the leftover. The truth is in between, and depends on how you stagger the joints. Buy at least the area figure with waste, and look at the row figure if your walls are an awkward length for your boards.
For other wall coverings see the wainscoting calculator, the board and batten calculator and the siding calculator. Paint and finish quantities are in the paint calculator.
Assumptions and limits
- The wall is flat, the board is the same width along its length and the openings are entered as a total area.
- The visible face width and the board length are the numbers you enter.
- The waste allowance is your choice and starts at 10 percent as an example.
- Trim, nails, adhesive, caulk and finish are not included.
Frequently asked questions
How much shiplap do I need for a wall?
Multiply the wall length by the height, subtract the openings, add a waste allowance, then divide by the area one board covers. A 200 square foot wall with 10 percent extra and 5.5 inch by 8 foot boards needs 60 boards.
How much waste should I allow for shiplap?
The tool starts at 10 percent as an example. Diagonal layouts, many openings or a wall that does not match your board lengths call for more, while a simple wall may need less.
Is the width on the label the width I should enter?
No. Enter the visible face of the board after installation. It is smaller than the nominal width because of the lap or groove.
Can I reuse the offcut from one row to start the next?
Often yes, when it is long enough and the joints stay staggered. That is why the area method gives a lower count than the row-by-row check.