Breadboard End Movement Calculator
Breadboard ends cap a tabletop with grain running across the panel, which means the panel will try to expand and contract behind a fixed end. Get the slot sizes wrong and the top cracks or the end splits. This calculator estimates total seasonal movement across the panel width from your species shrinkage coefficient and expected moisture swing, then gives the elongated slot clearance to allow on each side of the glued center. Shrinkage and moisture values come from the Wood Handbook and your own climate, so they are editable inputs, never guessed.
Breadboard movement formula
Fractional movement = (coefficient / 100) * swing / FSP
Total movement = panel width * fractional movement
Slot clearance per side = total movement / 2
Edge peg travel = total movement / 2
Because the center is glued, the panel grows and shrinks symmetrically about the middle, so each outer peg moves about half the total. Slot the outer holes by at least that clearance on each side, plus a small margin.
Breadboard build notes
- Glue only the central few inches of the breadboard joint.
- Elongate outer peg holes; size the pegs to slide, not bind.
- Use tangential coefficients for flatsawn tops, radial for quartersawn.
- Assume a realistic local moisture swing, or measure it.
- Add a small margin to the computed clearance for safety.
Breadboard ends: frequently asked questions
Why do breadboard ends need elongated holes?
A breadboard end runs its grain across the panel's grain. The panel expands and contracts across its width with seasonal humidity while the breadboard end does not, so the outer tenon pegs must sit in elongated (slotted) holes that let the panel slide. A glued or pinned tight joint would crack the panel.
How much does a panel move seasonally?
Movement across the grain = panel width x shrinkage coefficient x moisture content swing / fiber saturation point. The shrinkage coefficient is species and grain specific (from the USDA Wood Handbook), and the moisture swing depends on your climate and whether the piece is indoors. Both are user inputs here.
How big should the breadboard slots be?
Center the middle peg with a snug hole and glue only the center. Make the outer peg slots wider than the peg by the expected movement, so half the total movement is allowed on each side of center. This calculator reports the total movement and the recommended slot clearance per side.
Should I glue the whole breadboard end?
No. Glue only the central few inches so the panel can move symmetrically about the center. The rest of the joint is held by pegs in slots, often with the slots elongated and the pegs slightly undersized, allowing free seasonal movement without splitting.
What moisture swing should I assume?
It depends on location and use. Indoor furniture in a climate-controlled home might swing only a few percent moisture content between seasons, while pieces exposed to large humidity changes swing more. Use realistic local figures or measure with a moisture meter; the calculator uses your input rather than a fixed guess.
Official sources
- USDA Forest Products Laboratory: Wood Handbook, shrinkage and moisture relations.
- USDA Forest Service: Forest Service research publications.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.