How to Lay Out and Cut a Stair Stringer: Framing Square Method

The stringer is the sawtooth backbone of a staircase: the angled board whose notched steps carry every tread and riser. A well-cut stringer makes the whole stair feel solid and uniform; a sloppy one telegraphs every error into bouncy treads, uneven risers, and a stair that never quite feels right. The good news is that laying out a stringer is a repeatable marking exercise, not freehand art. With a framing square, two stair gauges, and a patient hand on the saw, you can cut accurate stringers on your first try. Here is the full method, step by step.

What a stringer is (and the two kinds)

A cut stringer, also called a sawtooth or open stringer, has triangular notches cut out of a 2x12 so the treads sit directly on the flat of each cut. This is the standard for deck stairs and most residential stairs because the layout is straightforward and every cut is visible for inspection.

A solid (closed) stringer is left whole, and the treads are supported by cleats or metal brackets screwed to its face. Solid stringers keep more wood in the board, which makes them stronger and longer-lasting in wet locations, but the layout math is the same either way. This guide covers the cut stringer, since that is what most DIY builders cut.

Use a straight, dry 2x12. For exterior stairs, use pressure-treated lumber rated for ground contact. Sight down the board and reject anything with a twist, a big crown, or large knots where the notches will land. A crooked board makes a crooked stair no matter how careful your marking is.

Tools and materials

- Straight 2x12 long enough for the full stringer (calculate stringer length from your rise and run, then add a foot of working room)

- Framing square and a pair of stair gauges (small brass or plastic stops that clamp to the square)

- Tape measure, sharp pencil, and a combination square for marking the bottom and top cuts

- Circular saw with a sharp framing blade

- Handsaw or jigsaw for finishing corners

- Clamps, sawhorses, a level, and hearing and eye protection

Step 1: Calculate your rise and run

You cannot lay out a stringer until the stair geometry is settled. Divide the total rise (finished floor to finished floor) by your target riser height to get the riser count, then divide the total rise by that count for the exact riser height. It must be 7-3/4 inches or less per the IRC, and every riser must be within 3/8 inch of the others. Pair it with a tread depth (unit run) of at least 10 inches. If you have not run these numbers yet, use a stair calculator first and write down three numbers: exact riser height, tread depth, and riser count.

Step 2: Set the framing square

Clamp a stair gauge on the tongue (the short arm) of the framing square at your riser height measurement, and a second gauge on the blade (the long arm) at your tread depth. The gauges butt against the edge of the board and register the square in exactly the same position for every step, which is what keeps all the notches identical. Double-check both settings against your tape before you mark anything. A square set to 7-1/2 inches when your math said 7-5/16 will put a visible error into every single step.

Step 3: Mark the first stringer

Lay the 2x12 across sawhorses with the crown (the slight arch along its edge) facing up, which will become the top edge of the stringer. Start near one end and place the square so the riser gauge mark sits on the board's edge, then trace the outside of the square: the tongue gives you the riser cut, the blade gives you the tread cut. Slide the square along so the tread gauge lands exactly on the end of the tread line you just drew, and trace again. Repeat down the board for the full riser count. You are drawing a staircase profile on the edge of the board, one notch per step.

Step 4: Mark the bottom and top cuts

The bottom of the stringer needs a level cut to sit flat on the landing, and it must be shortened by one tread thickness. This is the step beginners miss: the first tread rests on the floor, not on a cut, so if you do not subtract the tread thickness (typically 1 inch for a 2x board or 1-1/2 inches for doubled treads), the bottom riser ends up taller than all the others by exactly that amount. Mark a line parallel to the first riser mark, offset down the board by one tread thickness, and cut there.

At the top, the stringer usually fastens to the deck rim joist, a header, or a hanger board. Mark a plumb cut (vertical when the stringer is in position) so the top bears fully against its support, and confirm the top tread will land flush with the finished upper floor.

Step 5: Cut, but do not overcut

Cut the notches with the circular saw, stopping the blade just short of each inside corner. Then finish every corner with a handsaw or jigsaw. This matters structurally: a circular saw that plunges past the corner line severs wood fibers at the narrowest point of the stringer, exactly where the load concentrates. A widely used rule of thumb is to keep at least 3-1/2 inches of solid wood at the narrowest point of each notch; overcutting eats directly into that margin. Take your time on the corners. The few extra minutes with the handsaw are what separate a stringer that lasts from one that cracks at the first heavy load.

Step 6: Test-fit the first stringer

Set the cut stringer in position and check three things. First, every tread cut should read level and every riser cut plumb with a torpedo level. Second, measure riser heights: the bottom riser (after your tread-thickness deduction) and the top riser must match the rest within 3/8 inch. Third, confirm the top lands flush with the finished floor above. If anything is off, adjust the layout marks, not the cut board; recut if needed. The first stringer is your master template.

Step 7: Trace the rest and install

Once the master fits, trace it onto the remaining stringer boards and cut them identically. Clamp boards together and cut in pairs if your saw can manage it, but verify each one against the master afterward. For a 36 inch wide stair, two stringers are the minimum; wider stairs need a center stringer so treads never span more than about 16 to 18 inches unsupported.

Fasten the stringers at the top with structural screws or joist hangers rated for the load, and anchor the bottoms so they cannot kick out: a cleat, a concrete anchor, or a notched bearing block on the pad. Then install treads (and risers, if any) with construction adhesive plus screws, which is the belt-and-suspenders combo that keeps stairs quiet.

Mistakes that ruin stringers

- Skipping the tread-thickness deduction at the bottom, which makes the first riser taller than the rest and fails the 3/8 inch uniformity rule on day one.

- Overcutting the inside corners with the circular saw, weakening the narrowest point of every notch.

- Using a twisted or crowned-down board, which bakes a wave into the finished stair.

- Marking from a rounded-over factory edge instead of a fresh reference face, which shifts every notch by the size of the roundover.

- Cutting all stringers before test-fitting the first one, which multiplies one layout error across the whole stair.

- Forgetting the top connection: a stringer held by toenails alone can pull away from the rim over time. Use proper hangers or structural screws.

Code notes worth remembering

The IRC caps risers at 7-3/4 inches, requires treads at least 10 inches deep, demands riser uniformity within 3/8 inch, and requires a handrail on stairs with four or more risers. None of those numbers are checked at the lumber pile; they are all decided at the layout stage described above. A stringer laid out with the framing square method, cut without overcuts, and test-fitted before the rest are traced will satisfy an inspector on dimensions alone. The rest of the inspection, footings, fasteners, and railings, is installation work that the layout makes possible.

Cut one stringer carefully, and the stair practically builds itself. Rush the layout, and every tread you install afterward just locks the error in place.