Precut Stair Stringers: Sizes, Limits and When to Cut Your Own

Most people grab precut stair stringers off the lumber yard rack assuming they will fit any set of steps, then discover the bottom step is two inches taller than the rest. Those ready-made stringers work beautifully for a specific range of heights, and they can save an afternoon of layout and cutting. Outside that range, they create uneven risers that trip people every single day.

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The short answer: precut stringers are a good choice when your total rise divides evenly into the stringer’s built-in riser height (usually about 7 to 7 1/2 inches), when you need three to five steps for a deck, shed, porch or landing, and when the run fits the space you have. If your total rise falls between sizes, or you need a long interior staircase, a custom layout is almost always the better path.

Here are the standard sizes, how to check fit before you buy, how to trim a precut stringer correctly, the code points that matter, and the situations where cutting your own from a 2×12 is worth the extra work.

What Precut Stair Stringers Are and Where They Fit

Precut stair stringers are pressure-treated (or sometimes untreated) 2×12 boards that come already notched with a sawtooth pattern of riser and tread cuts. You buy them by the number of steps, typically from one to seven, and they are sized for outdoor stairs where speed matters more than a perfect custom fit. Retail versions are almost always treated for ground contact or exterior use, which makes them a natural fit for decks, garden sheds and porch steps.

Typical dimensions look like this:

• Riser height: roughly 7 to 7 1/2 inches per step on most retail stringers
• Tread run: roughly 10 1/2 to 11 inches, sized so two 5/4 deck boards or a pair of 2x6s cover each tread
• Step counts: commonly 2, 3, 4, 5, 6 and 7 step versions
• Stock: nominal 2×12 lumber, which leaves about 3 1/2 to 5 inches of solid wood below the notches depending on the cut

Because the geometry is fixed, precut stair stringers only work when your project bends to their dimensions. That is the trade. You give up flexibility and gain speed.

How to Check Whether a Precut Stringer Will Fit

Everything starts with total rise, which is the vertical distance from the finished landing surface at the bottom to the finished surface at the top. Measure it with a level and tape at the exact spot where the stairs will land, not somewhere convenient, because yards and patios are rarely flat.

1. Measure total rise. Lay a long straightedge or a level on the deck surface, extend it past the edge over the landing spot, and measure straight down to the finished landing. If the landing will be a concrete pad or pavers that are not installed yet, measure to where their top surface will sit.
2. Divide by the stringer’s riser height. Say your total rise is 29 inches and the stringer has 7 1/4 inch risers. 29 divided by 7.25 equals 4, so a four-riser stair works perfectly.
3. Count risers versus treads. A stringer marked “4 step” can mean four treads or four risers depending on the maker. Read the label. Usually the top tread is the deck itself, so you end up with one fewer tread than risers.
4. Check the run. Multiply the number of treads by the tread depth and add the nosing. Make sure the stairs will not push into a walkway, a door swing or a property line.
5. Look at the remainder. If the division leaves a fraction, that leftover height ends up concentrated on one step. Up to about 1/4 inch spread across the stair can usually be adjusted. More than that and you need a different approach.

A good rule of thumb: if your total rise is within about half an inch of a clean multiple of the stringer’s riser height, precut stair stringers will work with a little trimming or a landing adjustment. If not, plan on a custom layout.

Tools and Materials You Will Need

Installing a precut stringer is a modest project, but a few tools make the difference between a solid stair and a wobbly one.

• Tape measure, 4 foot level and a framing square
• A circular saw with a sharp framing blade for trimming the bottom and top cuts
• A handsaw or jigsaw to finish cuts at the inside corners of notches without overcutting
• Structural screws or hot-dipped galvanized nails rated for treated lumber
• Galvanized or coated stringer hangers or a ledger board at the top
• Copper naphthenate or another end-cut preservative for any fresh cuts on treated wood
• Concrete pad, pavers on compacted gravel, or a treated kick plate for the bottom bearing
• Safety glasses, hearing protection and work gloves

A circular saw is the single most important tool here. Clean, square cuts at the top and bottom are what make the treads sit level.

Trimming Precut Stringers to Fit

Even when the math is close, you will often need to adjust the stringer. Do it the right way and the risers stay uniform. Do it the wrong way and you get one short or tall step, which is the most common stair trip hazard there is.

Adjusting for Tread Thickness

Precut stringers are cut for the rough framing, not the finished surface. When you add treads, every step rises by the tread thickness, including the bottom step. The top step does not change because the deck surface is already there. To keep every riser equal, cut the thickness of one tread off the bottom of the stringer. For 5/4 deck boards that is about 1 inch. For 2×6 treads it is 1 1/2 inches. Skipping this step leaves the bottom riser short and the top riser tall.

Shortening for a Lower Landing

If the rise is slightly short, you can take a little more off the bottom cut, but only up to a point. Every inch you remove makes the bottom step shorter than the others. Instead, consider raising the landing with an extra paver course or a thicker pad so the total rise matches the stringer.

Cutting Off Extra Steps

Some people buy a five step stringer and saw it down to three. That works as long as you cut along the existing riser and tread lines, keep the top cut matched to how it attaches, and seal the fresh end grain. Never cut through the solid “throat” of the board below the notches; that remaining wood is what carries the load.

Installing Precut Stringers Step by Step

1. Plan the width and spacing. Most residential stairs are at least 36 inches wide. Space stringers no more than about 16 inches apart for 5/4 deck board treads, or up to about 24 inches for 2x treads, following the tread manufacturer’s span guidance.
2. Prepare the bottom bearing. Set stringers on a concrete pad or on pavers over compacted gravel, never directly on soil. Call 811 before digging for any footings or a pad.
3. Attach the top. Fasten stringers to the rim joist with stringer hangers or to a treated ledger that is bolted through the rim. The top of each stringer’s first tread cut should sit one riser below the deck surface.
4. Check every stringer for level and alignment. Lay a level across the tread cuts of all stringers. Shim or trim until they agree.
5. Brace the bottom. Tie stringers together with a treated kick plate anchored to the pad, which keeps them from spreading or sliding.
6. Install risers and treads. Attach riser boards if you want closed risers, then fasten treads with two fasteners per stringer per board. Leave a small gap between boards for drainage.
7. Add handrails. Attach a graspable handrail anchored into framing. Posts should be bolted into the stringers or the rim, not just screwed into tread boards.

Code Checks That Matter

Local building codes govern stairs, and most US jurisdictions follow similar residential rules. Confirm the details with your building department, but these are the typical targets:

• Maximum riser height: usually about 7 3/4 inches
• Minimum tread depth: usually about 10 inches, measured nosing to nosing
• Uniformity: risers and treads within a flight generally may not vary by more than 3/8 inch
• Handrails: commonly required once there are four or more risers, mounted about 34 to 38 inches above the tread nosings
• Guards: often required where the stair side is more than 30 inches above grade
• Width and headroom: typical minimums are about 36 inches wide and 6 feet 8 inches of headroom

Many retail precut stair stringers sit comfortably inside these limits, which is part of why they exist. Your adjustments are what push a stair out of compliance, especially uneven bottom risers. Deck stairs often require a permit along with the deck itself, and HOAs may have their own rules.

When to Cut Your Own Stringers

Precut stringers are a shortcut, not a universal answer. Cut your own from straight, knot-free 2×12 stock when any of these apply:

• Your total rise does not divide cleanly into the available riser heights
• You need more than seven steps, or a long staircase with a mid-flight landing
• The stair is interior, where you want untreated lumber and a precise finished fit
• You want a shallower riser and deeper tread for comfort, such as stairs for older family members
• Space limits force a specific run length
• The stairs will carry heavy loads like a hot tub delivery path or a commercial use

Custom layout uses the same framing square method no matter the length: divide total rise into equal risers, choose a tread depth, mark with stair gauges, and cut. Layout and cutting from scratch are a separate skill set, but once you have done it, you will see why the precut version is limited.

Troubleshooting Common Problems

The Bottom Step Is Shorter Than the Rest

This almost always means the tread thickness was not subtracted correctly, or too much was cut from the bottom. Raise the landing with a thicker pad or paver course rather than trying to shim treads.

Stringers Are Bouncy

Bounce usually comes from stringers spaced too far apart, too little wood left below the notches, or a loose top connection. Add a center stringer, upgrade to proper hangers, and make sure the bottom is anchored.

Treads Rock or Slope

Stringers are not level relative to each other. Check with a level across the cuts and plane or shim the high or low spots before fastening treads.

Wood Is Splitting or Rotting at the Bottom

The bottom is sitting on soil or in standing water. Lift it onto concrete or pavers, seal cut ends with preservative, and improve drainage around the landing.

Cost Ranges

Precut stair stringers in treated lumber generally cost in the range of a modest amount per stringer for short versions up to a moderate amount for six and seven step models, depending on region and lumber prices. A typical three stringer deck stair with treads, hangers and fasteners often runs a few hundred dollars in materials. Hiring a carpenter to build a short deck stair can add several hundred to over a thousand dollars in labor, depending on height, railing and footing needs. Cutting your own saves little on materials but gives you exact control over the fit.

When to Call a Pro

Bring in a licensed contractor or carpenter when the stair is tall, carries a permit requirement, connects to a deck whose ledger or footings you are unsure about, or needs guards and handrails on a raised flight. A pro is also wise for any structural question, such as whether the rim joist can carry the stair load or whether footings must go below frost depth. Wind and snow loads matter in some regions, and a professional will know local requirements. Safe stairs are about consistency and secure anchoring, and an experienced builder gets both right the first time.