Learn & Understand

Laying Out a Stair Stringer: The Framing-Square Method and the Drop

The companion calculator works out even riser heights, the safety-critical foundation of any staircase. Turning those numbers into an actual stringer, the sawtooth board that carries the treads, requires a layout method and a subtle adjustment that trips up first-time stair builders. Understanding how a framing square lays out the notches, why the bottom step must be shortened by a "drop," and the difference between cut and housed stringers is what turns correct riser math into a staircase that ends up level and even.

The Stringer Is a Repeated Right Triangle

A stair stringer is essentially a series of identical right triangles marched up a board, each triangle's vertical leg the riser height and its horizontal leg the tread depth. Laying it out means marking those triangles accurately and repeatedly along the stringer, then cutting out the notches. Because every riser must be equal for safety, as the calculator ensures, every triangle must be identical, so the layout method's whole job is to reproduce the same rise-and-run triangle precisely, step after step, without accumulating error down the board.

The Framing Square and Stair Gauges

The traditional tool for this is the framing square, a large L-shaped square, fitted with stair gauges, small clamps set on the square's two arms at the riser height and the tread depth.

With the gauges clamped at the calculated rise and run, you slide the square along the stringer board and trace the same triangle for each step, the gauges guaranteeing identical dimensions every time. This is the classic, reliable way to transfer the riser math onto the wood without measuring each step separately, which would invite the small errors that make risers uneven.

The Drop: Why the First Step Is Different

Here is the adjustment that catches beginners. Once the treads are installed, each tread adds its own thickness on top of the stringer notch. If the stringer's bottom step is cut to the full riser height, the first step will end up too tall by one tread thickness (and the top step too short) once the treads go on. To correct this, the bottom of the stringer is shortened, "dropped", by the thickness of one tread, so that after the treads are installed every finished riser, including the first and last, comes out equal. Forgetting the drop is a classic error that produces an uneven, code-violating first or last step despite perfect riser math. The drop reconciles the bare stringer with the finished, tread-covered staircase.

Cut vs Housed Stringers

Stringers come in two main forms. A cut (or notched) stringer has the sawtooth profile cut into its top edge, with treads sitting on the exposed notches, common and straightforward but it weakens the board by removing material. A housed stringer has the treads set into routed grooves (dados) in the inner face of a solid, un-notched board, stronger and cleaner-looking, with the tread ends hidden, but more work to make. The choice affects strength, appearance, and construction method, but both rely on the same accurate riser-and-run layout underneath.

From Riser Math to a Real Stringer

Use the calculator to fix even riser heights, then lay the stringer out faithfully: use a framing square with stair gauges set to the rise and run to mark identical triangles up the board, remember to drop the bottom by one tread thickness so the finished steps come out equal, and choose a cut or housed stringer for the strength and look you want. The calculation gives the risers; the layout method and the drop are what turn them into a level, even, safe staircase.