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Box Joint Calculator

Calculate finger joint count, actual width, glue surface area and strength vs butt joint. Enforces the odd-number rule for matching pairs.

Equal Finger SpacingOdd-Number RuleGlue Surface AreaStrength vs ButtPDF Report
📦

Box Joint — Calculator

Calculate finger joint count, actual width, glue surface area and strength vs butt joint. Enforces the odd-number rule for matching pairs.

Setup
Unit
Application
Router Bit / Saw Width
Board Dimensions
Board Width
mm
Board Thickness
mm
Finger Width (bit)
mm
✓
Box Joint Results
—
fingers
Number (odd)
—
mm
Actual Finger Width
—
mm²
Total Glue Area
—
× butt
Strength Ratio
Box Joint Preview
Formula Trace
📦 Box Joint Calculator
Box joint (finger joint) maximises glue surface area for strong attractive corners. Odd finger count ensures two identical pieces interlock when one is rotated 180°. Standard for drawers, boxes, crates and structural timber splicing.
Where Used?
Drawer BoxesWooden BoxesStructural SplicesCabinet CarcassesDecorative Crates
Formulas
N (odd) = nearest odd to (W / finger_width)Actual fw = W / NGlue area = 2 × N × fw × thicknessStrength ratio = glue_area / (W × thickness) [typically 3–6×]
FAQ
Why must fingers be odd?
For two identical pieces to interlock when one is flipped 180°, the pattern must start and end with the same element. Odd count ensures this. Even count creates a half-space mismatch at one end.
Ideal finger width for drawer boxes?
For 18mm stock: 10–12mm fingers for balanced look. Narrower (6–8mm) looks more refined. For structural applications use fingers equal to material thickness for maximum bearing area.
ResourcesView the formulasFormula Library
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