How to Make Stair Stringers

by Tom Matthews

Stair stringers are the backbone of a staircase, providing the structural support needed to hold up the treads and risers. Properly calculating and cutting stair stringers is essential for ensuring a safe, stable, and aesthetically pleasing staircase that meets building code requirements.

Understanding Stair Stringers

Stair stringers are the diagonal supports that run from the bottom to the top of a staircase and are typically notched to hold the treads (the horizontal steps) and risers (the vertical parts between the steps). Typically, a staircase has at least three stringers: one on each side and one in the middle for added support in wider stairs.

Each wooden stringer should be made from a 2x12-inch board of the straightest possible lumber with the fewest knots. Boards smaller than 2x12 inches do not leave enough wood to carry the load of the stairs after the cuts are made. Start with boards that are about 12 inches longer than the total length of the stringer.

Tools and Materials Needed

• Tape measure

• Carpenter’s square (AKA a framing square)

• Pencil

• Saws (circular saw and handsaw)

• Level

• Calculator

• Ruler or straightedge

• 2x12 lumber (pressure-treated for ground contact if building outdoors)

A Look at the Basics of a Pro-Grade Project

Code Requirements

It’s important to check your local building codes for guidelines such as allowable riser height and tread depth. For example, the International Residential Code states that maximum stair-riser height is 7-3/4 inches, and this measurement cannot vary more than 3/8 of an inch along the stairs. Minimum tread depth is 10 inches (plus a required nosing of at least 3/4 inch, although a tread of at least 11 inches requires no nosing).

Each stringer should be made from a 2x12-inch board of the straightest possible lumber with the fewest knots.

You will have additional code factors to consider, such as the minimum width for residential stairs should be no less than 36 inches. Stairs must maintain 80 inches of headroom throughout the walkway. Every landing must have a minimum depth, measured parallel to the direction of travel, equal to the width of the stairway or 48 inches, whichever is less.

There is also a detailed code section on handrail construction (although stairs less than 30 inches in height require no handrail). These variable factors are why stair-building is typically left to professional carpenters, but a diligent DIY homeowner can also construct (or repair) a simple outdoor staircase to access decks, porches, patios, etc. by following these basic guidelines.

Measure the Total Rise and Run

Total Rise: Measure the vertical distance from the top of the lower floor to the top of

the upper floor. This is the total rise of the staircase.

Total Run: Measure the horizontal distance the staircase will cover. This is the total run of the staircase.

Once you have the overall rise and run of the stairs, you can calculate how long the stringer needs to be. You can use a stair calculator or do the math yourself. To calculate the length yourself, you will need to use the Pythagorean theorem, which is a2 + b2 = c2. The “a” and “b” represent the rise and run.

Determine the Number of Steps

To find the number of steps, divide the total rise by the height of step rise (usually between

7 to 8 inches).

For example, if the total rise is 96 inches and the step rise is 7-1/2 inches:

Number of Risers = Total Rise ÷ Step Rise

Number of Risers = 96” ÷ 7-1/2”

Number of Risers = 12.8

Round this number to the nearest whole number. In this case, you’ll need 13 risers. Since you need one less tread than the number of risers, you'll need 12 treads.

Calculate the Step Run

To find the step run (the horizontal part of each step), divide the total run by the number

of treads. For instance, if the total run is 120 inches:

Step Run = Total Run ÷ Number of Treads

Step Run = 120” ÷ 12 Treads

Step Run = 10”

Once you know the number and depth of steps, you can work out where your landing pad needs to be.

Determine the Angle of the Stringer

Determine the angle at which the stringers should be cut using a framing square.

Place a framing square near the end of a 2x12 board, leaving several inches at the end before the end of the square. The board should be at least 12 inches longer than the planned length of the stringer. Use the individual rise and run figures marked on the outside scales of the square that matches your desired measurements. These figures should touch the upper edge of your board.

Set the framing square on the board so the measurement on the short end (the tongue) aligns with the step rise and the measurement on the long end (the body) aligns with the step run. Mark the outline along the square's outer edges. The angle where the two legs meet will give you the cut angle for the stringers. The angle cut at the end of the stinger will be parallel to the step riser.

This is the outline of your top stair.

Mark the Stringer

Slide the square down the board, making sure to line up the scale's rise and run figure at the top edge. Mark the new outline and repeat the process for each step until you have marked one extra pair of runs and rises.

In order to make the bottom step the same height as the others, you need to subtract the thickness of the tread board from the bottom rise.

Once you’ve cut your first stringer it can be used as a tracing template for the other stringers.

Site Conditions and Adjustments

Additional factors will come into play when calculating stringer size. For example: Will the stringer connect to the upper landing flush with the outer frame, or will it be recessed and anchored with hardware?

You should understand that this article contains the most basic stair-building guidelines, and that the easiest and ideal stair calculations often become complicated due to allowable space, structural transitions and other such site conditions. In fact, building stairs for your deck or porch is often considered the most difficult part of a construction project. Adjustments to one aspect of the stair’s design will impact other aspects of the stair’s design, and everything must fit mathematically.

For example, a shorter rise may be more comfortable to climb with a deeper run. Similarly, a taller rise might work better with a shorter run. Check your local building codes for allowable tread rise and run.

To illustrate the challenge of adjusting the calculations, let’s say we’re building a staircase with 13 risers of 7-3/8 inches to overcome and 8-foot total rise. If we apply a 10-1/2-inch step run to the staircase, the stringer length will be 12 ft. 10-1/6 inches, and the stringer angle will be 35.12 degrees.

However, if we shorten the step run to 10 inches on the same staircase, it changes the stringer length to 12 ft. 5-3/16 inches and changes the angle to 36.44 degrees.

Overcoming these design hurdles to build a perfect staircase is how skilled carpenters make a good living. It’s not always easy, and you shouldn’t let this brief overview of the basics give you the false impression that constructing a new staircase is a simple endeavor.

Construction calculators are available with various stair-building applications which simplify the design procedure for contractors.

Cut the Stringers

Double-check all measurements before cutting and always wear appropriate safety gear when using power tools. Carefully cut along the marked lines. Ensure you make straight, clean cuts to avoid uneven steps. Pro tip: Avoid completing the intersecting notch cuts with a circular saw because the overcut produced by the shape of the blade will weaken the stringer. Complete the intersecting notch cuts with a straight blade such as a handsaw or jigsaw.

Note that depending on your design, the step-run measurement might differ slightly from the final tread depth, because the tread may include nosing which would make the board deeper than the stringer notch.

A circular saw can be used to begin the notches, but the intersecting cuts should be completed with the straight blade of a handsaw or jigsaw to avoid over-cutting.

The first stringer can be used as a template for the other stringers. In this case, this stringer also served as the template for matching composite fascia board to cover each side of the staircase.

The fascia board that matches the stringer is cut with the saw blade tilted at an angle.

The bevel cut of the stair fascia provides a sleek trim detail as it transitions to the new composite decking.

Check and Install

Place the stringer in position and check for level and fit. Make any necessary adjustments.

Secure the stringer to the staircase frame with the appropriate metal hardware. Make

sure it is level, plumb, and properly supported. Typically, you'll need at least three stringers for standard stairs: one on each side and one in the middle for support.

Final Considerations

Keep in mind that for short staircases, home supply centers sell precut stair stringers that include between three and seven steps. Because the precut stringer design won’t be adjustable, you’ll need to construct the upper and lower landing to accommodate, but this

can provide a labor-saving solution for many stair projects.

For most construction projects, stringer design is best left to experienced professionals, However, by following these steps, a diligent DIY’er can accurately calculate and cut stair stringers to ensure a sturdy and safe staircase. If you're unsure or this is your first time, it might be helpful to consult with a professional or use stair-design software to double-check your calculations.

Construction of the staircase is underway. Note the excavation at the bottom of the stringer where a concrete landing will be formed and poured.

The completed deck stairs.

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Side Note 1

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Use the Construction Master Pro to complete stair layouts, including riser height and solve for the stairwell opening. Calculator features include built-in right-angle solutions;

areas, volumes, square-ups; roof, rafter and framing solutions; circles (including arcs, circumference, segments); drywall panels; studs on-center; compound miter cuts; arched

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Side Note 2

Evolution Steel Stair System

At the 2025 International Builders’ Show, Fortress Building Products exhibited its Evolution steel stair system components and brackets to provide quick, easy assembly, dramatically decreasing installation time.

The stair system's Black Sand powder-coat delivers an aesthetically pleasing modern look on its own or use it with fascia/trim for a more traditional look. As a noncombustible material, the system is resistant to fire and invulnerable to rotting, warping, splitting and pesky insect damage. It cuts down on the number of stair stringers required and eliminates the need of spacing 10, 12 or 16 inches on-center. The system includes three different rise/run bracket options and a fully adjustable stair bracket. The system is compatible with any type of deck framing, even wood, and it carries a 25-year limited manufacturer warranty. www.fortressbp.com