Stair Stringer Calculator

Last updated: 27 Nov 2025 | Author: Brij | Review By: Irshad

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A simple Stair Stringer Calculator that helps you find the number of steps, riser height, tread run, stair angle, and stringer length using minimal inputs. Includes formulas, and a full example for easy understanding.

Total Rise:

Total Run:

Tread Depth:

Riser Height:

Stair Stringer Calculation Results

Number of Steps:

steps

Actual Riser Height:

Actual Tread Run:

Stringer Length:

Stair Angle:

Designing a safe and comfortable staircase starts with calculating the correct number of steps, riser height, tread run, and the stringer length. A Stair Stringer Calculator helps you do this quickly by using just a few basic measurements.

This guide explains all required inputs, outputs, formulas, and a full example so you can verify every calculation easily.

Formulas Used in the Stair Stringer Calculator

1. Number of Steps

The number of steps depends on the Total Rise divided by the Riser Height.

Formula

$Steps = \frac{Total\ Rise}{Riser\ Height}$

2. Actual Riser Height

Since the number of steps must be a whole number, we recalculate the true riser height.

Formula

$Actual\ Riser\ Height = \frac{Total\ Rise}{Steps}$

3. Actual Tread Run

The run of each step depends on the Total Run divided by the number of treads.

Formula

$Actual\ Tread\ Run = \frac{Total\ Run}{Steps}$

4. Stringer Length

The length of the stair stringer is the hypotenuse of a right triangle.

Formula

$Stringer\ Length = \sqrt{(Total\ Rise)^2 + (Total\ Run)^2}$

5. Stair Angle

The angle of the stair is found using trigonometry:

Formula

$Angle = \tan^{-1}\left(\frac{Total\ Rise}{Total\ Run}\right)$

Example Calculation

Let’s calculate a simple staircase:

Total Rise = 9 ft (108 in)
Total Run = 11 ft (132 in)
Riser Height = 7.5 in
Tread Depth = 10 in (not used in minimal formula, but good for design)

1. Number of Steps

$Steps = \frac{108}{7.5} = 14.4 \approx 14$

2. Actual Riser Height

$Actual\ Riser\ Height = \frac{108}{14} = 7.71\ in$

3. Actual Tread Run

$Actual\ Tread\ Run = \frac{132}{14} = 9.43\ in$

4. Stringer Length

$Stringer\ Length = \sqrt{108^2 + 132^2}$

$Stringer\ Length = \sqrt{11664 + 17424} = \sqrt{29088} = 170.5\ in$

5. Stair Angle

$Angle = \tan^{-1}\left(\frac{108}{132}\right)$

$Angle = \tan^{-1}(0.818) = 39.3^\circ$

FAQs

1. What is a stair stringer?

A stair stringer is the structural support board that holds the treads and risers of a staircase. It runs diagonally from the top floor to the bottom floor and carries the weight of the steps.