Wood Shiplap Calculator: Boards Needed by Wall Area
Subtract the overlap (rabbet) width from the board’s actual milled width to get its real wall coverage, then divide your total wall square footage by that coverage width to find how many linear feet — and how many stock boards — of shiplap you need.
Quick Answer
Subtract the overlap (rabbet) width from the board’s actual milled width to get its real wall coverage, then divide your total wall square footage by that coverage width to find how many linear feet — and how many stock boards — of shiplap you need.
Wood Shiplap Calculator: Boards Needed by Wall Area
Enter your values below for an instant result, then see the formula, worked example, and common mistakes.
Enter your wall area and board size, then click calculate.
How to Use This Calculator
Get the total square footage of the wall (height x width), subtracting large openings like windows and doors if you want a tighter estimate.
Shiplap sold as “1×6” or “1×8” refers to nominal size — the actual milled width is smaller (a 1×6 is 5.25 in wide, a 1×8 is 7.25 in wide). Check the product label, since widths vary slightly by supplier.
Shiplap boards interlock with a rabbeted edge, and that overlap does not add new wall coverage — typically 0.375 to 0.5 in is lost per board. This is usually listed in the product spec sheet.
Common stock lengths are 6, 8, 10, and 16 ft. Match this to your wall height or run to minimize seams and waste.
10% covers a simple rectangular wall; use 15% for walls with many corners, outlets, or a pattern that requires matching.
Formula
Coverage width per board = Actual board width – Overlap. Total linear feet = Wall area (sq ft) / Coverage width (ft). Boards needed = Total linear feet / Board length, rounded up and adjusted for waste.
Reference Table: Common Shiplap Sizes
| Nominal size | Actual face width | Typical overlap | Approx. coverage width |
|---|---|---|---|
| 1×4 | 3.5 in | 0.375-0.5 in | ~3.0-3.1 in |
| 1×6 | 5.25 in (varies 5.25-5.5 in) | 0.375-0.5 in | ~4.75-5.0 in |
| 1×8 | 7.25 in | 0.375-0.5 in | ~6.75-6.9 in |
Common Mistakes to Avoid
- Using the nominal board size (1×6, 1×8) instead of the actual milled width — a 1×6 board is only 5.25 in wide, not 6 in, which will under-order material if used directly.
- Forgetting to subtract the overlap/rabbet — the overlapped portion of each board does not add new visible wall coverage, so skipping this step overestimates coverage and under-orders boards.
- Not checking the exact overlap spec for your specific product — it varies by manufacturer (commonly 0.375 to 0.5 in), and using the wrong figure compounds error across a whole wall.
- Ignoring window and door openings when they are large, which can meaningfully reduce the true square footage that needs covering.
- Ordering board lengths that do not match wall height well, creating unnecessary horizontal seams and extra waste from off-cuts.
When the Estimate May Be Wrong
This calculator estimates linear footage and board count for vertical or horizontal shiplap installed over a flat wall area. It assumes a consistent overlap/rabbet across all boards and does not account for pattern-matching (e.g. herringbone), extensive outlet/switch cutouts, or non-rectangular wall shapes. Always verify your specific product’s actual width and overlap dimensions on the packaging before ordering, since these vary between suppliers.
FAQs
Is shiplap sold by its nominal or actual size?
Shiplap is labeled by nominal size (like 1×6 or 1×8), but the actual milled width is smaller — a 1×6 is about 5.25 in wide and a 1×8 is about 7.25 in wide.
Why does the overlap matter for calculating shiplap coverage?
The rabbeted overlap where one board interlocks with the next does not add new visible wall coverage, so it must be subtracted from the board’s actual width to get the true coverage width per board.
How much waste should I add when ordering shiplap?
10% is typical for a simple rectangular wall. Increase to 15% or more for walls with many corners, outlets, or a pattern that requires matching.
What is the most common shiplap board size for walls?
1×6 and 1×8 are the most common nominal sizes for interior accent walls, with 1×8 covering more area per board and requiring fewer total pieces.
Sources and Methodology
Actual milled width and overlap figures cross-referenced against Lowe’s shiplap wall plank product specifications, Calculator Academy’s Shiplap Calculator methodology, and TexasVJoint’s shiplap coverage guide. Waste factor guidance (10% simple walls, 15% complex) reflects standard interior trim installation practice.
