What length screw for 3/4 plywood?
Joining 3/4" plywood to 3/4" plywood, use a 1 1/4" screw. It buries two thirds of the second sheet and stops short of the far face. Screw lengths for every common joint.
Screwing 3/4" plywood to 3/4" plywood, use a 1 1/4" screw.
It goes 1/2" into the second sheet — 67% of it — and leaves 1/4" of wood past the tip. Anything between 1 1/8" and 1 3/8" would do, and 1 1/4" is the only stocked length in that window.
How that is worked out
- The threads do no work in the first board, so the screw needs its full 3/4" to get through it.
- Then two thirds of the second board: 3/4" × 2/3 = 1/2". 3/4" + 1/2" = 1 1/4".
- The limits either side: at least half the second board for the threads to hold (1 1/8"), and the tip at least 1/8" short of the far face (1 3/8").
Screw length by joint, nearest stocked length to two thirds' penetration
| Through | Into | Ideal | Buy | Every length that fits |
|---|---|---|---|---|
| 1/2" | 3/4" | 1" | 1" | 1" |
| 3/4" | 3/4" | 1 1/4" | 1 1/4" | 1 1/4" |
| 3/4" | 1 1/2" | 1 3/4" | 1 3/4" | 1 1/2", 1 5/8", 1 3/4", 2" |
| 1/2" | 1 1/2" | 1 1/2" | 1 1/2" | 1 1/4", 1 1/2", 1 5/8", 1 3/4" |
| 5/8" | 1 1/2" | 1 5/8" | 1 5/8" | 1 1/2", 1 5/8", 1 3/4", 2" |
| 1 1/2" | 1 1/2" | 2 1/2" | 2 1/2" | 2 1/2" |
| 1 1/2" | 3 1/2" | 3 13/16" | 4" | 3 1/2", 4" |
Worth knowing
- Two thirds is the shop rule, and half is the floor: below 50% of the receiving board there is not enough thread in it to hold.
- Into the edge of plywood, the plies want a pilot hole and a screw no thicker than a #8, or the edge splits along a glue line. The pilot hole calculator gives the bit.
- A screw through the face of one sheet into the edge of another can go longer, because the edge has the full width of the board in front of the tip. These figures are for face to face.
Work out your own numbers
- Screw length
How long a screw to put through one board into another, and whether the tip comes out the far side.
- Pilot hole calculator
The right drill bit for a wood screw, by gauge number and by softwood or hardwood.
- Pocket hole screw calculator
Screw length and thread by material thickness, and how far apart to space the holes along an edge joint.
Related questions
- What size screws to join two pieces of 3/4 plywood?
- 1 1/4", usually a #8. It bites 1/2" into the second sheet and the tip stops 1/4" short of coming through.
- What length screw for 1/2 inch drywall into a stud?
- 1 1/2" by this rule, which puts 1" of thread into the stud. Anything from 1 1/4" to 1 3/4" fits the stud; drywall screws are designed to hold with less bite than a wood screw, which is why 1 1/4" is the common choice.
- Is a 1 1/2 inch screw too long for 3/4 plywood?
- For 3/4" into 3/4", yes — the joint is only 1 1/2" thick, so the tip would come out of the far face. The longest that stays inside is 1 3/8".