How to Make a Stair Tread Jig (Quick and Easy!)

Getting accurate length and angle measurements for stairs can be tricky with just a tape measure, but a stair tread jig makes the job much easier. So let's step into the shop and build one together out of a few simple items you probably already have on hand!

Materials & Tools:

1. Circular saw
2. Jigsaw
3. Drill, drill bit, countersink bit (sizes dependent on bolt size)
4. Measuring tape
5. ¾" plywood scraps
6. Two bolts and nuts (wingnuts optional, but recommended)
7. Pencil and square

This is the spine of your jig — mine measures 32" x 6½", but size yours to fit what you're working on. Keep in mind the length of your spine needs to be less than the width of the space you're trying to measure.

1. Rip a strip of ¾" plywood at 6½" wide
2. Cut it down to about 32" long (or more if you need longer reach)

These ends form the trapezoid sliders that represent your stair tread shape.

1. Cut two pieces to be 9¼" deep (the depth of your stair treads)
2. Taper each into a trapezoid — wide end about 9¼", narrowing to match your spine width (approx. 6½")

Tip: I used a circular saw for the bulk of the cut, and a jigsaw for those tight inner corners.

Next, you'll need to create the slots that allow the adjustable end caps to slide to your desired length. To do this:

1. Drill a countersink hole near the narrower edge of each trapezoid piece, about ½" in from the end. This will be what the head of your bolts sit in, to allow them to be flush with the plywood.
2. Using a smaller drill bit, drill the rest of the way through the material where you added your countersink hole. This hole will need to be large enough to accept the thread of the bolt, but not allow the head to pass through -- choose your drill bit size accordingly.

Once you're holes are drilled, test fit your bolt to make sure it will slide easily, but the head catches properly.

These slots allow the end pieces to slide in and out to match line up with the width of whatever you're measuring!

1. Line up the trapezoid ends flush with the center beam ends
2. Mark the innermost point (ideally, don’t let the slot go past this. I accidentally messed this up on mine, but it doesn't effect the function of the jig.)
3. On the spine, cut a centered slot about 3/8" to ½" wide using a jigsaw. The size of the slot will be dependent on the diameter of the bolt you chose.

1. Insert bolts through the end pieces and into the slots
2. Tighten nuts with socket wrench. Or better yet, upgrade to wingnuts for easier adjustments!
3. Test the sliding motion — it should move smoothly but lock down tight

That's it! Super easy, right?

Wanna see what I did with mine? I built this jig to help with a full stair tread replacement. You can see how I used it here:

👉 Watch the full stair makeover video