Shiplap Calculator
Use this shiplap calculator to estimate boards, rows, coverage area, linear feet, and optional material cost. Enter a wall, ceiling, or total area, then set the exposed board width, board length, openings, and waste.
Results
Shiplap estimates depend on the actual exposed face width, board length, room shape, and how seams land. Use this as a material count before checking the product label and your final layout.
How to use this calculator
- 01Choose wall, ceiling, or total area mode.
- 02Enter the wall, ceiling, or measured project area. Add openings for parts that will not receive shiplap.
- 03Enter the exposed board width. Use the visible face, not the nominal board width.
- 04Enter board length and waste percentage. Ten percent is a common starting point for simple layouts.
- 05Add price per board if you want a material cost estimate.
Understanding the math
Shiplap takeoff starts with the area that will receive boards. The calculator subtracts openings, adds waste, then divides by one board's coverage. Wall and ceiling modes also estimate courses because they have a layout direction. Total area mode skips those rows because square footage alone does not say how the boards run.
Gross wall area = wall width x wall height x wall count Gross ceiling area = ceiling length x ceiling width Net shiplap area = max(gross area - openings, 0) Order area = net area x (1 + waste / 100) Board coverage area = board length x exposed width Boards to buy = order area / board coverage area Linear feet with waste = order area / exposed width
Example: a 12 ft x 8 ft wall with 5.5 in exposed boards, 8 ft board length, and 10 percent waste has 96 sq ft of wall area. The order area is 105.6 sq ft. Each board covers about 3.67 sq ft, so the estimate rounds up to 29 boards. That gives 232 purchase linear feet.
Shiplap quick reference
Use these common shiplap values as a starting point. Product labels and actual board exposure should win when they differ.
| Item | Value | Notes |
|---|---|---|
| Common exposed board widths | 5 to 7 in | Use the visible face, not the nominal board name |
| Common board lengths | 8, 10, 12 ft | Longer boards reduce seams but can be harder to handle |
| Default waste factor | 10% | Good starting point for straight walls or simple ceilings |
| Wall course rule | height / exposed width | Round up to the next full course |
| Ceiling course rule | ceiling width / exposed width | Cut length is the ceiling length in this estimate |
| 8 ft board at 5.5 in exposure | 3.67 sq ft | Board coverage before waste |
Frequently asked questions
How to calculate shiplap?
Measure the wall or ceiling area, subtract openings, then add waste. Divide the order area by one board's coverage. Board coverage is board length times exposed board width in feet. Round up because partial boards still have to be bought.
How many shiplap boards do I need?
Divide the waste-adjusted project area by the coverage of one board. For example, an 8 ft board with 5.5 in of exposed width covers about 3.67 sq ft. A 105.6 sq ft order area needs 105.6 / 3.67 = 28.8, so buy 29 boards.
How do you calculate coverage for shiplap?
Coverage for one board equals board length times exposed board width. Convert exposed width to feet first. A 5.5 in exposure is 0.458 ft, so an 8 ft board covers 8 x 0.458 = 3.67 sq ft before waste.
How to calculate shiplap for ceiling?
Multiply ceiling length by ceiling width, subtract any openings, and add waste. Use ceiling width divided by exposed board width to estimate the number of courses. The cut length per course is the ceiling length in this simple takeoff.
How much does it cost to shiplap a 10x10 room?
Cost depends on wall height, openings, exposed board width, board length, waste, and price per board. Four 10 ft wide by 8 ft high walls have 320 sq ft before openings. After subtracting openings and adding waste, multiply boards to buy by the board price.
What are common shiplap mistakes?
Common mistakes are using nominal board width instead of exposed width, skipping waste, forgetting openings, and assuming total area can predict course layout. Rows and cut length need wall or ceiling dimensions, not just square footage.
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