What is a half-lap joint?

A half-lap joint is where half the thickness is removed from each piece so they overlap flush. The finished joint is the same thickness as one of the original pieces. It is commonly used for frames, cross-braces, and lattice work.

How strong is a lap joint?

Lap joints have large glue surface areas, making them reasonably strong in shear. They are weaker than mortise and tenon joints in tension. Adding screws or dowels significantly increases strength. They are ideal for frames and stretchers.

Can I cut lap joints on a table saw?

Yes, lap joints are easily cut with a dado blade on a table saw, or by making multiple passes with a standard blade. A mitre gauge or crosscut sled ensures accurate, square cuts.

WoodCalcs.uk

Lap Joint Calculator — Overlap Joint Dimensions

Calculate lap joint dimensions and material removal for half-lap, full-lap, and dovetail-lap joints.

Piece 1 Thickness

Board thickness — for a half lap, half of this is removed as the notch

Piece 1 Width

Board width — this sets the width of the notch (housing) cut into Piece 2

Piece 2 Thickness

Board thickness — for a full lap no material is removed, so the joint stacks to the combined thickness

Piece 2 Width

Board width — this sets the width of the notch (housing) cut into Piece 1

Lap TypeHalf lap removes half from each piece; full lap removes nothing (one piece sits on top, joint = combined thickness); dovetail lap adds an angled tail to resist pull-apart

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.