Shiplap profile cross-sections — nominal vs actual vs net coverage width
No “1×6” covers 6″: rabbeted pine covers 5″, nickel-gap T&G covers 4⅝″, pattern T&G covers 5⅛″. Rows = wall span ÷ net coverage — always the exposed face, never the nominal size.
What this diagram shows
Three wall cross-sections through a shiplap joint comparing the common profiles, each dimensioned with actual milled width in gray and net exposed coverage in blue. A traditional rabbeted pine 1×6 mills to 5-1/2 inches but its half-inch lap leaves only 5 inches of coverage. A nickel-gap tongue-and-groove 1×6 mills to 5-5/16 inches and covers 4-5/8 inches after the tongue and the 1/8-inch reveal. Tongue-and-groove pattern pine 1×6 mills to 5-3/8 inches and covers 5-1/8 inches with a tight reveal. No "1×6" covers 6 inches — rows or runs are solved as wall span divided by NET COVERAGE, the exposed face width, which varies by brand even at the same nominal size.
Shiplap Calculator
Free shiplap calculator: exact board or pack count from the real exposed coverage width, not nominal size. Horizontal, vertical & ceiling runs.
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