Stair Stringer Calculator with Landing: How to Use

This stair stringer calculator with landing works out the exact length, angle, and number of steps for a straight staircase that includes a mid-way landing. You enter the total rise, total run, landing position, and tread thickness, and it returns the stringer dimensions, step rise/run, and the angle of the stringer cut. The result lets you lay out and cut a pair of stringers confidently, whether you are building a deck, porch, or interior stair.

Formula

The calculator uses the standard stair geometry formulas. First, it estimates the number of risers by dividing the total rise by a comfortable step height (about 7.5 inches) and rounding to the nearest whole number. Then it divides the total rise by that number to get the exact step rise. The total run is the horizontal distance from the top of the stairs to the bottom, including the landing. The landing depth is subtracted from the total run to find the horizontal distance available for the steps themselves. That distance is divided by the number of treads (which is one less than the number of risers) to get the step run. The stringer angle is the arctangent of rise divided by run, and the stringer length is the hypotenuse of the right triangle formed by the total rise and the horizontal run of the steps.

Variables:

• Total rise (in) – vertical distance from the lower floor to the upper floor, measured from finished floor to finished floor.
• Total run (in) – horizontal distance from the face of the upper floor (or landing) to the face of the lower floor, including the landing depth.
• Landing depth (in) – horizontal length of the landing measured along the direction of travel.
• Tread thickness (in) – thickness of the tread material (e.g., 1.5 in for 2×6 decking).
• Step rise (in) – vertical height of each step.
• Step run (in) – horizontal depth of each tread (the actual walking surface, not including nosing).
• Stringer angle (deg) – the angle of the stringer cut relative to horizontal.
• Stringer length (in) – the length of the stringer board measured along the slope, from the top cut to the bottom cut.

Worked Example

Using the default values: total rise = 105 in, total run = 120 in, landing depth = 36 in, tread thickness = 1.5 in.

1. Estimate number of risers: 105 / 7.5 = 14.0, so round to 14 risers.
2. Step rise = 105 / 14 = 7.5 in.
3. Horizontal run for steps = total run – landing depth = 120 – 36 = 84 in.
4. Number of treads = risers – 1 = 13.
5. Step run = 84 / 13 = 6.46 in.
6. Stringer angle = atan(7.5 / 6.46) = 49.3 degrees.
7. Stringer length = sqrt((7.5 * 14)^2 + (6.46 * 13)^2) = sqrt(11025 + 7045) = sqrt(18070) = 134.4 in.

The calculator displays: step rise 7.50 in, step run 6.46 in, angle 49.3°, stringer length 134.4 in. Note that a step run of 6.46 inches is quite short – in practice you would adjust the total run or landing depth to get a more comfortable tread depth (usually 10-11 inches).

How a Landing Affects Stringer Calculations

A landing is a flat platform that breaks a staircase into two or more flights. When you add a landing, the stringer does not run continuously from top to bottom; instead, each flight has its own stringer. The landing itself takes up horizontal space and vertical height. In the calculator above, the landing is assumed to be at the same slope as the stairs, meaning the total rise is divided evenly across all risers, including the one that lands on the platform. This is a simplification – in reality, the landing may be at a different elevation, or the stairs may turn 90 or 180 degrees. For a straight stair with a mid-landing, the total rise is still the full vertical distance, and the total run includes the landing depth. The calculator treats the landing as just another tread, which is correct when the landing is the same height as a step and the stairs continue in the same direction.

How to Use the Calculator for Your Project

To get accurate results, you need to measure the actual rise and run on site. Use a level and a tape measure to find the vertical distance from the finished floor below to the finished floor above. The total run is the horizontal distance from the face of the upper floor (where the stringer attaches) to the face of the lower floor, measured along the stair path. If you have a landing, measure its depth along the direction of travel. Enter those numbers, plus the tread thickness (usually 1.5 in for 2×6 or 2×12 decking, or 1 in for 5/4 decking). The calculator then gives you the exact rise and run per step, the stringer angle, and the length of the stringer board. Use these numbers to lay out the stringer on a 2×12 or 2×10 board, marking the rise and run on the square, and cutting the notches.

Common Mistakes and How to Avoid Them

• Forgetting to subtract the landing depth: If you enter the full run without subtracting the landing, the step run will be too large, and the stairs will not fit.
• Not accounting for tread thickness: The first riser height must be reduced by the tread thickness to keep all steps equal. This calculator does not adjust for that – you must subtract the tread thickness from the bottom riser when cutting.
• Using the wrong number of risers: Always round to the nearest whole number, but check that the resulting rise is within building code limits (typically 7-8 inches). If not, adjust the total rise or add a step.
• Measuring run from the wall instead of the nosing: The run should be measured from the face of the upper floor to the face of the lower floor, not including any overhang.
• Ignoring the stringer thickness: The stringer board itself has thickness (usually 1.5 in), which affects the actual cut length. The calculator gives the theoretical length; you may need to add a little for the bottom cut.

Building Code and Safety Considerations

Most building codes specify that the maximum riser height is 7.75 inches and the minimum tread depth is 10 inches (with nosing). The minimum width of a stair is usually 36 inches. For a landing, the depth must be at least as long as the width of the stair, but not less than 36 inches. Always check your local code before building. The calculator helps you get the geometry right, but it does not replace a structural review – stringers must be sized correctly (usually 2×12 for spans up to about 6 feet), and the landing must be supported properly. Use the calculator to verify that your rise and run fall within code limits; if not, adjust the total run or the number of steps.

Alternatives and When to Use Them

If you are building a curved, spiral, or multi-flight stair with turns, this straight-stringer calculator is not suitable. For those, you need a dedicated spiral stair calculator or a professional design. Also, if your landing is not at the same elevation as a step (e.g., a half-height landing), you need to calculate each flight separately. Some builders prefer to use a steel stringer or a pre-fabricated stair system, which have their own sizing charts. But for a simple straight stair with a mid-landing, this calculator gives you the core dimensions quickly and accurately.

Frequently Asked Questions

How do I measure the total run for a stair with a landing?

Measure the horizontal distance from the face of the upper floor (where the top stringer attaches) to the face of the lower floor, following the path of the stairs. Include the landing depth – that is the horizontal length of the landing platform measured in the direction you walk. If the landing is not directly in line, break the measurement into segments and add them.

What is the ideal step rise and run?

Comfortable stairs typically have a rise between 7 and 7.75 inches and a run (tread depth) between 10 and 11 inches. The sum of two rises plus one run should be around 25 inches (the “blondel” formula). For example, 7.5 + 7.5 + 10 = 25. Use the calculator to see if your dimensions are close; if not, adjust the total run or the number of steps.

Do I need to subtract the tread thickness from the first riser?

Yes. If you attach treads on top of the stringer, the first riser (at the bottom) will be effectively taller by the tread thickness if you don’t subtract it. The standard practice is to cut the bottom of the stringer shorter by the tread thickness so that all risers are equal. This calculator does not do that automatically – you must adjust the bottom cut manually.

Can I use this calculator for a deck stair with a landing?

Yes, as long as the landing is straight and at the same elevation as a step. For a deck, measure the total rise from the ground to the deck surface, and the total run from the deck edge to the point where the stairs meet the ground, including the landing. Enter those numbers and the calculator will give you the stringer dimensions.

What if my landing is not at the same height as a step?

Then you need to calculate each flight separately. Determine the rise to the landing, then use the calculator with that rise and the run for that flight. Repeat for the upper flight. The landing itself must be framed independently, and the stringers for each flight are cut separately.

Why is my calculated step run too short?

This usually happens when the total run is too small relative to the rise, or when the landing depth is too large. The calculator divides the remaining run by the number of treads – if that number is less than 10 inches, you need to increase the total run (make the stairs longer) or reduce the landing depth. Alternatively, you can increase the number of steps (which reduces rise) but that also reduces run per step, so you may need to adjust both.

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in t | Total rise | in | 105 | 0
in r | Total run | in | 120 | 0
in l | Landing depth | in | 36 | 0
in th | Tread thickness | in | 1.5 | 0
out rise | Step rise | in | t / round(t / 7.5) | 2
out run | Step run | in | (r - l) / (round(t / 7.5) - 1) | 2
out angle | Stringer angle | deg | atand(rise / run) | 1
out length | Stringer length | in | sqrt((rise * round(t / 7.5))^2 + (run * (round(t / 7.5) - 1))^2) | 1