Cut one stringer wrong and every step on the staircase inherits the error. A clean stair stringer layout is really just careful arithmetic followed by careful pencil work, and the arithmetic is where most first-timers go sideways. The stringer is the sawtooth board that carries the treads and risers, and its notches have to divide your total height into equal steps that meet building code. This guide shows how the numbers work, how to mark them with a framing square, and where the code limits sit, so you understand the plan even if you hire the cutting out.
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Start With Total Rise, Not Guesswork
Total rise is the vertical distance from the lower finished floor to the upper finished floor. Measure it dead accurate, because a quarter-inch mistake here multiplies across every step. Hold a level straight edge out from the top landing, then measure straight down to the floor below. Do this in two or three spots, since floors are rarely perfectly flat, and use the number that keeps you honest.
Say your total rise is 108 inches. You divide that height into a whole number of equal risers. Aim for a comfortable riser height near 7 inches, then divide 108 by 7 to get about 15.4. You cannot have a fractional step, so round to 15 or 16 risers. Divide 108 by 15 and you get 7.2 inches per riser. Divide by 16 and you get 6.75 inches per riser. Both land in the legal range, so you pick based on how much horizontal room you have.
Understand the 7-11 Rule
The comfort standard many builders quote is the 7-11 rule: a riser around 7 inches paired with a tread run around 11 inches. Under the widely used International Residential Code, the maximum riser height is 7 and 3/4 inches and the minimum tread run is 10 inches. There is also a rule that the difference between the tallest and shortest riser in a flight cannot exceed 3/8 inch, which is why equal division matters so much.
Run is the horizontal depth of each tread, measured nose to nose, not counting the nosing overhang. Count risers and treads and you will notice there is always one more riser than there are treads, because the top step’s riser is the landing itself. If you have 15 risers, you have 14 treads. Multiply 14 treads by an 11-inch run and you learn the staircase eats about 154 inches, just under 13 feet, of floor length. Check that against your available run before you commit, because a steep space may force you to a code-legal but tighter number.
Do the Full Math With a Real Example
Keep working the 108-inch example. Choose 15 risers at 7.2 inches each. That gives 14 treads. Pick a run of 11 inches per tread. Now you have every number the stringer needs.
- Total rise: 108 inches
- Number of risers: 15
- Unit rise per step: 7.2 inches
- Number of treads: 14
- Unit run per step: 11 inches
- Total run: 154 inches
Before you cut anything, account for the finished floor and the tread thickness, an adjustment carpenters call dropping the stringer. If you mark the bottom riser at the full 7.2 inches and then add a tread on top, that first step ends up taller than the rest once the tread thickness stacks on. To fix it, you trim the bottom of the stringer by the thickness of one tread, minus the finished floor thickness at the top. This is the single detail beginners forget, and it is what keeps all your risers equal.
Mark the Stringer With a Framing Square
The framing square is the classic tool for this. Set stair gauges, the little brass buttons that clamp to the square, at 7 and 3/16 inches on the tongue for the rise and 11 inches on the body for the run. Rounding 7.2 to 7 and 3/16 keeps you inside the readable marks on the square, and the tiny difference gets absorbed across the flight.
Lay the square on the stringer stock, usually a 2×12, and slide it until both gauges touch the top edge of the board. Trace along the outside of the square to mark one riser line and one tread line. Slide the square down the board so the next rise line starts where the last run line ended, and repeat. Fifteen times you step the square down the board, and the notches march along in a perfect sawtooth. Number each step as you go so you do not lose your place.
Check Before You Cut
Once every notch is marked, stand back and verify. Count the risers and treads and confirm they match your plan. Measure two or three notches to confirm the rise and run are consistent. A framing square set with gauges is very repeatable, but a slipped gauge or a board with a crown can throw off a step.
Cut just shy of the lines with a circular saw, then finish the inside corners with a hand saw or jigsaw so you do not overcut and weaken the board. Overcutting past the corner is a real strength issue, since a 2×12 with slashes through the notch roots can crack under load. Use the first stringer as a template to trace the others so all three or four match exactly. Most residential stairs 36 inches wide use three stringers, one on each side and one in the middle, with wider stairs adding more.
Cut Stringers vs Solid Stringers
Not every staircase uses the notched, sawtooth stringer. There are two broad approaches, and the layout math is the same, but the cutting and appearance differ. A cut stringer, also called an open stringer, is the notched 2×12 where the treads and risers sit on the exposed steps. This is the common choice for basement stairs, deck stairs, and utility runs because it is straightforward and shows the classic stepped profile from the side.
A housed or closed stringer keeps the outer board solid and routes shallow grooves into its inside face to receive the treads and risers, which are then wedged and glued in place. You see this on finished staircases where a clean, uninterrupted side board looks more refined and hides the joints. Housed stringers require a router and a template and are more of a finish-carpentry task. For most DIY and utility projects, the cut stringer is what you will lay out and build, but it helps to know why a nicer staircase looks different from the side.
Whichever you use, the number of stringers matters for strength. A 36-inch-wide residential stair typically uses three, spaced evenly, so the treads do not flex underfoot. Wider stairs or thinner tread stock call for more. Skimping on the middle stringer is a common cause of bouncy, squeaky steps that annoy you for years, so do not leave it out to save one board.
Material and Tread Choices
Stringers are usually cut from 2×12 dimensional lumber, since a 2×10 does not leave enough solid wood behind the notches once you cut the sawtooth. For exterior stairs, use pressure-treated lumber rated for ground contact and fasteners approved for treated wood, because untreated framing rots fast where it meets the ground and weather. Interior stringers can be standard framing lumber, though many builders choose a straight, low-crown board and set the crown up.
Tread thickness feeds back into your layout through the drop-the-stringer adjustment mentioned earlier, so decide on treads before you cut. Common tread stock includes 2x lumber for utility stairs, engineered stair-tread boards for interior finish work, and hardwood treads over a subtread for a stained finish. Each has a different thickness, and that thickness is what you subtract at the bottom of the stringer to keep the first and last risers equal to all the others. Measure the actual board you plan to use rather than trusting a nominal size, since a nominal 2x is really about 1.5 inches thick.
Know When to Call a Pro and Pull a Permit
Stairs are a fall hazard and a structural element, so most jurisdictions require a permit and an inspection for a new or rebuilt staircase. Handrail height, guardrail spacing, headroom clearance of at least 6 feet 8 inches, and stringer attachment all get checked. Local code can differ from the model code, so confirm the exact riser maximum, tread minimum, and material requirements with your building department before cutting lumber.
If your total rise is unusual, the space is tight, or the stairs turn with a landing or winders, the layout math gets complicated fast, and a small error becomes a trip hazard someone lives with for decades. There is no shame in having a carpenter cut the stringers while you handle the treads and finish. A sound stair stringer layout is the backbone of a safe staircase, so treat the numbers with respect, double-check every measurement, and lean on a licensed pro whenever the geometry moves past a simple straight run.
