How to Make a Stair Stringer: A Step-by-Step Guide for Homeowners

A single miscut on a stringer can throw off every tread by a fraction of an inch, and by the time you stack that error across five or six steps the whole flight feels wrong underfoot. Learning how to make a stair stringer is really about disciplined measuring and clean layout more than fancy carpentry. Get the rise-and-run math right, mark it carefully, and the cutting is the easy part. This guide walks you through the planning, the numbers, and the failure points so your stairs feel solid on the first step and the last.

What a Stringer Actually Does

The stringer is the sawtooth-shaped board that carries the treads and, in most cases, the risers. It transfers everything walking down the stairs into the framing above and the landing below. A typical residential flight uses three stringers on a 36-inch-wide stair: one on each side and one in the center to stop the treads from flexing. Wider stairs may need a fourth.

Most stringers are cut from 2×12 pressure-treated or standard lumber. You want a straight, dry board with no large knots along the cut line, because knots weaken the thin material left behind after notching. Crowned lumber should be installed crown-up, but honestly, for a stringer you want the flattest board on the rack.

The Math: Total Rise, Rise Per Step, and Run

Everything starts with total rise, which is the finished vertical distance from the lower floor to the upper floor. Measure this precisely, accounting for finished floor thickness on both ends. Say your total rise is 108 inches. Building codes in most of the US cap the maximum riser height at 7 3/4 inches, so divide 108 by 7.75 to get 13.9, which rounds up to 14 risers. Now divide 108 by 14 to get a rise per step of about 7.71 inches. That number must stay consistent, because code allows only 3/8 inch of variation between the tallest and shortest riser in a flight.

Run is the horizontal depth of each tread, minus nosing. Code sets a minimum tread depth of 10 inches. Many builders use a 10 1/2-inch or 11-inch run for a more comfortable stride. Remember that a flight with 14 risers has 13 treads, since the top riser lands you on the upper floor. Multiply 13 treads by your run to find how much horizontal space the stairs consume. With an 11-inch run, that is 143 inches, or just under 12 feet of floor length.

Tools and Materials You Will Need

You do not need a huge kit, but the right tools make the layout far more accurate.

• Framing square with stair gauges (the small brass buttons that clamp to the square)
• Circular saw and a sharp handsaw or jigsaw to finish the corners of each notch
• Tape measure, sharp pencil, and a speed square
• 2×12 lumber for the stringers, rated for the location (pressure-treated outdoors)
• Construction adhesive, framing nails or structural screws, and joist hangers or a ledger for the top connection

Laying Out the First Stringer

Clamp your stair gauges to the framing square at your rise number on the tongue (the narrow leg) and your run number on the body (the wide leg). Using 7.71 rise and 11 run, set the gauges as close to those marks as your square allows. Start at one end of the board and slide the square down so both gauges touch the top edge of the lumber. Trace along the outside of the square to mark the first tread and riser. Slide the square to the next step, line the gauge back up to your last mark, and repeat all the way down. Number each step as you go so you do not lose count.

After marking all 14 risers and 13 treads, you have to account for two adjustments before cutting. The bottom of the stringer needs to be trimmed by the thickness of one tread so your finished rise stays uniform. This is called dropping the stringer. If your treads are 1 inch thick, cut 1 inch off the bottom rise line. Skipping this step is the single most common mistake, and it makes your first step too tall and your last step too short.

Cutting the Notches Cleanly

Set your circular saw to follow each layout line, but stop exactly at the inside corner where the tread and riser meet. Overcutting past that corner weakens the stringer and leaves an ugly visible slot on the exposed side. Finish each corner with a handsaw or jigsaw so the cut is square and the corner stays sharp. Take your time on the first stringer, then use it as a template to trace the other stringers. Tracing the template beats re-measuring each board, because it guarantees all your notches match.

Once cut, stand the stringer against the framing and check that every tread notch sits level and every riser reads plumb. A small torpedo level on a couple of notches tells you fast if your layout drifted. If one notch is off, it is far cheaper to catch it now than after the treads are screwed down.

Attaching Stringers and Meeting Code

The top of the stringer typically hangs from a ledger board or attaches to the header with metal hangers rated for the load. The bottom sits on the lower floor, often against a kickplate or anchored to the slab. Because stairs carry concentrated loads and failure here can cause serious falls, this connection is one worth confirming against your local building code, and in many jurisdictions interior and exterior stairs require a permit and inspection. If you are unsure whether your header can carry the load, have a licensed contractor or building official review the framing plan before you commit.

Space your three stringers evenly across the stair width, roughly 16 inches on center for standard tread material, tighter if you are using thinner treads that could flex. Run a bead of construction adhesive on the notch before setting each tread to kill squeaks, then fasten with screws rather than nails for a connection that will not work loose over the years.

Common Mistakes That Ruin a Stringer

Beyond forgetting to drop the stringer, watch for these errors. Inconsistent riser heights top the list, usually from sloppy gauge alignment on the square. Cutting stringers from a bowed or heavily knotted board is another, since the weak spot often lands right at a notch. People also forget that the finished floor at the top and bottom changes the effective rise, so measure to the finished surfaces, not the subfloor, whenever you can.

One more: guardrails and handrails are part of the job, not an afterthought. Any flight with four or more risers generally requires a graspable handrail, and open sides need a guard. Plan those attachment points while the framing is exposed, because retrofitting a solid handrail mount later is a headache.

Cut Stringers vs Solid Stringers

There’s more than one way to carry treads, and it’s worth knowing your options before you start cutting. A cut, or open, stringer is the sawtooth style described here, where notches are cut into the board and the treads sit on top of the exposed steps. It’s the most common for basement, deck, and utility stairs because it’s straightforward and the treads are easy to fasten.

A solid, or housed, stringer keeps the board’s full width and uses routed grooves or cleats on the inside face to support the treads, hiding the step profile behind a clean, closed side. This style is common on finished interior staircases where you want a polished look and maximum strength, since the board isn’t weakened by notching. For most DIY projects a cut stringer is the practical choice, but if strength or a finished appearance matters, understand that a solid stringer is stronger because it retains the full depth of the lumber.

Material Choices and Longevity

The lumber you choose affects how long the stairs last, especially outdoors. For interior stairs, a straight, dry construction-grade board like a 2×12 in fir or SPC works well and stays stable in a conditioned space. For exterior stairs, use pressure-treated lumber rated for ground contact if the bottom will sit near soil or concrete, since untreated wood exposed to moisture will rot and weaken right where the load concentrates.

Fasteners matter just as much as the wood. Outdoors, use hot-dipped galvanized or stainless-steel structural screws and connectors, because standard fasteners corrode quickly when they contact the chemicals in treated lumber and the moisture outside. Seal or stain exterior stringers and treads to slow weathering, and keep the bottom of the stringer off direct contact with soil or standing water using a proper base or kickplate. These choices are what separate stairs that last a couple of years from ones that stay solid for decades.

Final Checks Before You Trust the Stairs

Before you load the stairs, walk them slowly and feel for any step that reads high or low. Set a 4-foot level across the treads to confirm they are level front to back, ideally with a barely perceptible 1/8-inch pitch to shed water on exterior stairs. Confirm the total run fits your space and that headroom above the flight meets the 6-foot-8-inch minimum most codes require. Knowing how to make a stair stringer pays off every single day you use those stairs, so spend the extra hour on layout. Careful math and clean cuts are what separate a flight that feels rock solid from one that creaks and wobbles.