How to calculate the first stringer rise

Correct the timber so the finished step is right

The lower floor has no tread board sitting on a stair notch, while the first step does. Without accounting for that difference, adding the first tread makes the bottom finished rise too tall. The bottom cut resolves that mismatch while keeping the repeated notch layout consistent.

This is useful to think through whenever the tread material is changing. A thicker tread is not just a different surface finish; it changes the relationship between the bearing cut and the first finished step. Establish all finish elevations and the actual tread thickness before cutting the pattern.

Why the bottom cut is different

The stringer layout describes the rise from one framing notch to the next, but the finished tread sits on top of each notch. At the first step, that added tread thickness would make the finished rise too tall unless the bottom of the stringer is shortened by the same amount.

Raise the level bottom cut by the tread thickness. This shortens the first timber rise without changing the repeated rise-and-run layout.

First stringer rise = exact finished riser − tread thickness

A simple example

If the exact finished riser is 7 1/2 inches and the finished tread is 1 inch thick, the vertical distance from the level bottom cut to the first tread seat is 6 1/2 inches. Once the 1-inch tread is installed, the first finished rise is 7 1/2 inches—matching the others.

Avoid the common mistakes

• Do not subtract tread thickness from every riser notch.
• Use the actual finished tread thickness, not the nominal lumber name.
• Include flooring or landing finishes in the original total-rise measurement.
• Recalculate if the tread material changes after layout.
• Check the first and last finished risers before cutting the remaining stringers.