Stair Calculator
Calculate stair dimensions including number of risers, treads, stringer length, and angle. Verify building code compliance and get material estimates.
About this calculator
Number of Risers starts from dividing Total Rise by Target Riser Height and rounding to the nearest whole riser, then Actual Riser Height is recalculated by dividing Total Rise back by that whole-number riser count -- so your target riser height is a starting point, not a guarantee; the final riser height is whatever makes the stair rise exactly, evenly, in a whole number of steps. Total Rise and Target Riser Height pull the riser count in opposite, closely matched directions: more total height means more risers, while a taller target riser height means fewer, and across this calculator's input ranges neither one reliably outweighs the other.
Number of Stringers is a simple two-value rule completely separate from the riser math: 3 stringers for stairs up to 36 inches wide, 4 for anything wider, with no reference at all to Total Rise, Target Riser Height, or Tread Depth. Total Run (Horizontal) then follows directly from Tread Depth once the tread count is fixed, and Stringer Length is the Pythagorean hypotenuse of Total Rise and Total Run, so it grows with the stair's overall footprint even when the riser count itself stays constant.
Inputs
Results
Number of Risers
15
How to Use This Calculator
- Measure the total rise (floor to floor) in inches — a standard 9-foot ceiling is 108 inches.
- Enter your target riser height in inches (code maximum is 7.75 inches).
- Set the tread depth in inches (code minimum is 10 inches).
- Enter the stair width in inches (minimum 36 inches per IRC).
- Read the calculated number of risers and treads, actual riser height, total run, stringer length, stair angle, and code compliance status.
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How the result changes with Total Rise (Floor to Floor)
| Total Rise (Floor to Floor) | Number of Risers |
|---|---|
| 42 | 6 |
| 86 | 12 |
| 138 | 20 |
| 182 | 26 |
What each input means
- Total Rise (Floor to Floor)
- Total vertical height from bottom floor to top floor (typically 9 ft = 108 inches).
- Target Riser Height
- Ideal height for each step (code max 7.75").
- Tread Depth
- Depth of each step (code min 10").
- Stair Width
- Width of the staircase (code min typically 36").
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersTotal Rise (Floor to Floor) = 108, Target Riser Height = 7, Tread Depth = 10, Stair Width = 36 = 4 input(s) provided
- Calculate Number of RisersNumber of Risers15 = 15
- Calculate Number of TreadsNumber of Treads14 = 14
- Calculate Actual Riser HeightActual Riser Height7.2 = 7.2
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.
Frequently Asked Questions
Why doesn't my Actual Riser Height match my Target Riser Height exactly?
The calculator rounds Total Rise divided by Target Riser Height to the nearest whole number of risers, since a real staircase cannot have a fractional step. Actual Riser Height is then Total Rise divided by that rounded riser count, so it only equals your target when the division happens to come out even.
Does Total Rise or Target Riser Height matter more for Number of Risers?
Neither input structurally dominates the other -- Number of Risers comes from dividing Total Rise by Target Riser Height, so raising the total height and lowering the target riser height both push the riser count up by comparable amounts across this calculator's ranges.
Why does Stringers Needed only have two possible values?
Number of Stringers follows a fixed rule with no dependence on the rest of the stair geometry: 3 stringers for a staircase up to 36 inches wide, 4 stringers for anything wider. Total Rise, Target Riser Height, and Tread Depth play no role in that decision at all.
How does Tread Depth affect Total Run and Stringer Length?
Total Run (Horizontal) is Tread Depth multiplied by the fixed number of treads, so a deeper tread directly lengthens the horizontal footprint. Stringer Length then grows along with it, since it is calculated as the Pythagorean hypotenuse of Total Rise and Total Run.
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