Framing
Stair Stringer Calculator
Input your total rise and get the precise stringer cuts for your next staircase. This tool calculates the exact riser height, total run, stringer length, and the bottom riser deduction automatically.
Stair Dimensions
Calculation Results
Exact Riser
Bottom Cut
Total Run
Stringer Length
14 risers and 13 treads.
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Understanding the Math
Laying out stair stringers requires precision to ensure every step is exactly the same height. Even a slight variation can cause a trip hazard.
Bottom Riser Deduction
The very bottom riser cut on your stringer must be shorter than the rest. You must deduct the thickness of your tread material so that once the tread is installed, the first step matches the exact height of the other steps.
Stringer Length
The stringer length is the diagonal hypotenuse of the total rise and total run. Make sure to buy lumber that is slightly longer than this calculated length to account for the angle cuts at the top and bottom.
The Math Behind Stair Stringers
Laying out stair stringers requires precision. Even a slight variation can cause a trip hazard. Here is how the calculator computes the layout:
| Calculation | Formula | Notes |
|---|---|---|
| Number of Risers | Total Rise ÷ Target Riser Height | The exact vertical drop divided by your ideal step height, rounded to the nearest whole number. |
| Exact Riser Height | Total Rise ÷ Number of Risers | The actual height of every step. This must be exact so every step is identical. |
| Bottom Cut | Exact Riser Height − Tread Thickness | The very bottom riser cut on your stringer must be shorter than the rest. You must deduct the thickness of your tread material so the first step matches the rest once treads are installed. |
| Stringer Length | √(Total Rise² + Stringer Run²) | The stringer length is the diagonal hypotenuse (Pythagorean theorem). Buy lumber slightly longer than this calculated length to account for the top and bottom angle cuts. |
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Frequently Asked Questions
How do I measure total rise for stairs?
Measure the exact vertical distance from the finished lower floor surface to the finished upper floor surface.
What is the standard riser height?
Most building codes dictate a maximum riser height of 7 3/4"197mm, though a target of 7" to 7 1/2"178mm to 190mm is generally preferred for comfort.
What is the ideal tread depth (run)?
Building codes generally require a minimum tread depth of 10"254mm, though 11"279mm is preferred for comfort and safety.
Why do I need to deduct the tread thickness from the bottom riser?
If you don't cut the bottom of the stringer shorter by the exact thickness of your tread material, your very first step will be taller than all the rest once the treads are installed, creating a major tripping hazard.
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