Lap Joint Calculator — Overlap Joint Dimensions
Calculate lap joint dimensions and material removal for half-lap, full-lap, and dovetail-lap joints.
How We Calculate This
This calculator determines the notch dimensions for lap joints.
Half lap
Each piece is notched to half its thickness. The notch width equals the width of the mating piece.
Full lap
In a full lap no material is removed from either piece — one board simply sits on top of the other and is glued (and usually screwed or dowelled) in place. The finished joint is the combined thickness of the two boards.
Dovetail lap
A dovetail lap is cut to the same depth as a half lap (commonly half the thickness, up to two-thirds under the tail), but one shoulder is angled to resist the joint pulling apart. Use roughly a 7° slope in hardwood and 9–14° in softwood when marking the tail.
Frequently Asked Questions
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Last updated: February 2026
All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.