Glue-Up Clamp Calculator
How many clamps an edge-to-edge glue-up needs, how far apart they go, whether it needs cauls, and how long to leave it in the clamps.
- Panel
- 48" by 24", 4/4 stock, 4 boards at 6"
- Glue
- Titebond II (Premium)
- Pressure
- 100 to 150 psi — Pipe or bar clamps
Alternate the clamps above and below the panel, which keeps it from bowing.
Pressure closes the joint and thins the glue line. It does not cure the glue: PVA cures by losing water.
Each caul is a pair of bars, one above the panel and one below, drawn together by a clamp at each end. That is 6 bars and 6 clamps on top of the 7 along the panel: 13 clamps in all.
At 24" wide this panel wants 3 cauls across the grain, about every 30", to hold it flat while it cures.
The layout
3/4" pipe is enough at this thickness.Where the clamps go
measured from the left end| Clamp | From the left end | Side |
|---|---|---|
| 1 | 2" | above |
| 2 | 9 3/8" | below |
| 3 | 16 5/8" | above |
| 4 | 24" | below |
| 5 | 31 3/8" | above |
| 6 | 38 5/8" | below |
| 7 | 46" | above |
Cauls
6 bars and 6 clamps, across the grain| Caul | From the left end |
|---|---|
| 1 | 5 11/16" |
| 2 | 27 11/16" |
| 3 | 42 5/16" |
How this is worked out
Clamp spacing comes from the thickness of the stock: about seven times it, held between 8" and 18". Thin stock would otherwise ask for more clamps than anyone owns, and thick stock would spread them so far apart that the middle of the joint starves. The clamps sit a couple of inches in from each end and spread evenly between, alternating above and below the panel so it is pulled straight rather than bowed.
Cauls are a different job. They run across the grain, on top of the panel, and their work is flatness rather than closing the joint. A panel 20" or wider is wide enough to lift in the middle, so it gets cauls about every 30".
The pressure figure does not change with the glue, because it is a property of the wood rather than the adhesive. PVA glue, which is what Titebond I, II and III all are, cures by losing water into the wood and the air. Pressure pulls the joint closed, squeezes the glue line thin, and stops the boards sliding. Past that it adds nothing, and enough of it pushes glue out of the joint and leaves it starved.
Clamp time and cure time are different things. The clamp time is when the panel can come out of the clamps and be handled. Full strength takes about a day, and a thick or humid glue line in Titebond III can want up to three.
How to use it
- Measure the panel along and across the glue lines.
- Enter the thickness in quarters, the way the stock is sold.
- Pick the glue, which sets the timings but not the pressure.
- Lay the clamps out at the spacing given, alternating above and below, and add the cauls if it asks for them.
- Dry fit everything first. A glue-up is the wrong time to find a clamp is too short.
What it assumes
- An edge-to-edge glue-up in flat, straight stock with joints that already close without force.
- Boards of equal width. The board width given is a target; the panel is divided evenly.
- PVA glue. Epoxy and polyurethane cure by chemical reaction and behave differently under pressure.
- Clamp spacing is a rule of thumb from thickness, not a calculation from clamping force.
- Times are for a normal shop, around 70°F. Cold or damp slows everything down.
Sources
- Wood glue: clamping and curing guidance — Titebond (Franklin International) (checked 2026-09-25)
- Wood Handbook: Wood as an Engineering Material, chapter 10, adhesion — USDA Forest Products Laboratory (checked 2026-09-25)
The example on this page is a 48" by 24" panel in 4/4 stock, which takes 7 clamps.