Stair Stringer Calculator - Risers, Treads & Stringer Length
Calculate actual riser height, number of treads, and stringer length from total rise, desired steps, and target tread depth.
in
in
Standard comfort range: about 10-11 in
Stringer Length
174.1 in
Number of Risers
14
Actual Riser Height
7.71 in
Number of Treads
13
Total Run
136.5 in
How Stair Stringer Dimensions Are Calculated
Enter the total rise — the full floor-to-floor height the staircase needs to climb — and either the number of steps you want or a target riser height (most building codes call for risers between about 7 and 7.75 inches for a comfortable climb). The tool divides the total rise evenly across that many risers, then uses your target tread depth (typically 10-11 inches) to work out the total run and the stringer length — the diagonal cut board that supports the stairs — via the Pythagorean theorem.
Number of Treads = Number of Risers − 1
Total Run = Number of Treads × Tread Depth
Stringer Length = √(Total Rise² + Total Run²)
Example
A 108-inch total rise split into 14 steps gives an actual riser height of 108 ÷ 14 = 7.71 inches — within the comfortable range. With 13 treads at 10.5 inches each, the total run is 136.5 inches, and the stringer length works out to √(108² + 136.5²) ≈ 174 inches.
Common Use Cases
- Planning a deck, porch, or basement staircase before cutting stringers.
- Checking whether a planned step count keeps risers within a comfortable, code-friendly range.
- Estimating the length of stringer lumber needed for a job.
- Working backward from a desired riser height to find how many steps a staircase needs.
FAQs
What riser height is considered comfortable or code-compliant?
Most residential building codes call for a riser height between roughly 7 and 7.75 inches, with treads around 10-11 inches deep. This tool flags whether your calculated actual riser height falls in that typical comfort range — always confirm exact limits against your local building code before building.
Why is the number of treads one less than the number of risers?
The top riser brings you up to the level of the upper floor itself, which already acts as the final "tread," so a staircase with a given number of risers only needs one fewer physical tread board.
Does the stringer length include extra length for the horizontal foot?
No — this calculates the theoretical diagonal length from the Pythagorean theorem using total rise and total run. In practice, always add extra length when cutting a real stringer board to account for the horizontal seat cut at the bottom and the thickness of the framing lumber it lands on.