Shiplap Calculator
Estimate net wall coverage, board quantity with waste, material cost, installation cost, and total project budget.
Project area
Board and cost assumptions
Live estimate
Calculation breakdown
| Step | Calculation | Result |
|---|---|---|
| Gross area | 8 ft × 16 ft | 128.00 ft² |
| Windows | 2 × 2 ft × 3 ft | 12.00 ft² |
| Doors | 0 × 3 ft × 7 ft | 0.00 ft² |
| Net area | 128.00 – 12.00 – 0.00 | 116.00 ft² |
| Board coverage | 8 in ÷ 12 × 8 ft | 5.33 ft² |
| Base boards | ceil(116.00 ÷ 5.33) | 22 boards |
| Boards with waste | ceil(22 × 1.05) | 24 boards |
Quantities are rounded up to whole boards. Verify the manufacturer's exposed face width, because the overlapping rabbet can make usable coverage narrower than the nominal board width.
How to use the shiplap calculator
What this calculator does
This calculator estimates the net surface area that will receive shiplap, the coverage of one board, the whole number of boards to purchase, and optional material and installation costs. It subtracts identical rectangular windows and doors from a rectangular wall, then adds a user-selected waste allowance before rounding the purchase quantity up. It is a planning estimate, not a structural design, fastening schedule, moisture assessment, contractor quotation, or substitute for the product manufacturer's installation instructions.
When to use it
Use it when budgeting an accent wall, ordering boards for a ceiling or other rectangular surface, comparing different board face widths and lengths, or checking how windows, doors, labor rates, and cutting waste change the project total. Measure each distinct wall separately when dimensions or openings differ, then add the resulting purchase quantities only after checking whether offcuts can be reused.
How to calculate
- The calculator opens with a complete demonstration: an 8 ft by 16 ft wall, two 2 ft by 3 ft windows, 8 in by 8 ft boards, 5% waste, a $2.50 board price, and $4.00 per ft² installation. The first estimate and Excel workbook are immediately available.
- Replace the demonstration measurements with your own. Use decimal feet for wall, window, door, and board length values; enter the board's exposed face width in inches.
- Set window and door counts. A zero count is valid; the related dimensions remain available for quick scenario changes.
- Keep Include waste allowance selected to add the percentage in Waste allowance, or clear it to estimate only the mathematical minimum.
- Read Boards to buy first, then review area, coverage, and cost results. Use the breakdown table to audit each step.
- Select Download Excel to export the current validated model. Reset clears the demonstration and calculated state, so Excel export becomes unavailable until a complete valid project is entered again.
Input guide
Wall height and Wall length are required positive decimal values in feet; 8 and 16 are realistic examples. Increasing either increases gross area and usually increases boards and cost. Do not enter inches in these fields. Number of windows and Number of doors are required whole numbers of zero or more. Their associated Window width, Window height, Door width, and Door height are decimal feet and must be nonnegative; when a count is positive, both dimensions must be greater than zero. The combined opening area cannot equal or exceed the gross wall area.
Board face width is the usable exposed width in inches, not necessarily the nominal milled width. For example, an 8-inch face and an 8-foot Board length cover 5.333 square feet. The exact relationship relies on 12 inches equaling 1 foot, as documented in the NIST tables of measurement units. Both board dimensions are required and must be greater than zero.
Include waste allowance is an on/off control. When selected, Waste allowance accepts 0% through 100%; 5% is the demonstration value. More waste can cover cuts, damaged pieces, pattern matching, and future repairs, but it also raises the purchase count and material cost. Price per board and Installation price are optional nonnegative U.S. dollar amounts. Enter plain decimal numbers such as 2.50 and 4; do not paste currency codes or formulas.
Output guide and worked example
Gross wall area is wall height multiplied by wall length. Openings area is the combined area of all listed windows and doors. Net project area is gross area minus openings and is the labor-cost basis. Board coverage is exposed width in feet multiplied by board length. Boards to buy is always a whole-number purchase estimate rounded upward after waste. Material cost equals boards to buy times price per board; Installation cost equals net area times installation price; and Estimated total cost adds those two estimates. A zero cost means the corresponding rate is zero, not that the project requires no material or labor.
For the startup example, gross area is 8 × 16 = 128 ft². Two windows remove 2 × 2 × 3 = 12 ft², leaving 116 ft². One board covers (8 ÷ 12) × 8 = 5.333 ft². The mathematical minimum is ceil(116 ÷ 5.333) = 22 boards. Applying 5% waste gives ceil(22 × 1.05) = 24 boards. Material is 24 × $2.50 = $60.00; installation is 116 × $4.00 = $464.00; total estimated cost is $524.00.
Planning assumptions and practical checks
The model treats every opening of a given type as the same size. For mixed window or door sizes, calculate opening areas separately and use equivalent dimensions only when that preserves the total, or run separate wall estimates. It also assumes the board face width and length represent usable coverage. Real installations may require trimming at corners, maintaining expansion gaps, matching courses, and rejecting damaged stock.
Wood changes dimension as moisture content changes. The U.S. Forest Service's guidance on drying and moisture control recommends installing wood near the moisture content it will experience in service to reduce seasonal movement. Before covering a wall, correct leaks and damp conditions; the EPA emphasizes that moisture control is central to mold prevention.
Main formula
Net area = wall height × wall length – window count × window width × window height – door count × door width × door height. Board coverage = board face width ÷ 12 × board length. Boards to buy = ceil(ceil(net area ÷ board coverage) × (1 + waste rate)).
Because both board counts are rounded upward, applying waste to the already rounded base quantity can add a board sooner than applying waste directly to square footage. This conservative purchase method is useful for retail ordering, where boards are indivisible. For expensive custom boards, compare the estimate with a cut plan and supplier packaging quantities before ordering.