Wood Stair Calculator
Estimate stringers, treads, risers, and cost for wooden stairs
Vertical height from floor to floor
Standard: 7 to 7.75 inches
Standard: 10 to 11 inches
Standard: 36 inches minimum
36" wide = 3, 48" wide = 4
Local price for 2x12 lumber
Number of Steps
—
steps
Actual Riser Height
—
in
Total Run
—
in
Stringer Length
—
in
Stringer Boards
—
boards
Tread Boards
—
boards
Estimated Cost
—
USD
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Building a wooden staircase requires precise measurements to ensure safety and code compliance. Our calculator helps you determine the number of steps, stringer length, and material needs.
- Measure the total vertical rise (floor to floor height)
- Choose a target riser height (7-7.75 inches is standard)
- Select a tread depth (10-11 inches is standard)
- Enter your stair width and number of stringers
- The calculator adjusts to the nearest whole step and recalculates actual riser height
Expert Insights
Smart analysis for your stair project
Rise + Run Rule
The sum of one riser and one tread should equal 17-18 inches for comfortable stairs. Our calculator flags combinations outside this range.
IRC Code Compliance
International Residential Code requires max 7.75" riser height and min 10" tread depth. Our calculator verifies compliance automatically.
Stringer Lumber
Always use 2x12 lumber for stringers. 2x10 boards do not leave enough wood after notching, creating a weak point at the throat.
Calculation Formula
Number of Steps = Total Rise / Desired Riser Height (rounded)
Actual Riser Height = Total Rise / Number of Steps
Total Run = (Number of Steps - 1) x Tread Depth
Stringer Length = sqrt(Total Rise^2 + Total Run^2)
Stair Component Comparison
| Component | Typical Size | Material | Notes |
|---|---|---|---|
| Stringers | 2x12 | Pressure-treated or Douglas fir | Notched to accept treads and risers |
| Treads | 1x10 or 2x10 | Pine, oak, or composite | Actual width often 9.25-11.25" |
| Risers | 1x8 | Pine or MDF | Optional for open-riser designs |
| Header Board | 2x10 | Matching framing lumber | Secures top of stringers |
Authority References
- International Residential Code (IRC) — R311.7 Stairways. Learn more
- OSHA — Stairway and Ladder Safety. Learn more
- AWC — American Wood Council Span Tables. Learn more
Frequently Asked Questions
What is the standard rise and run for stairs?
Standard rise is 7 to 7.75 inches per step. Standard run (tread depth) is 10 to 11 inches. The ideal sum of rise + run is 17-18 inches.
How many stringers do I need for a staircase?
For stairs 36 inches wide, use 3 stringers. For stairs 48 inches wide, use 4 stringers. Space stringers 16-18 inches on center.
What size lumber for stair stringers?
Use 2x12 lumber for stair stringers. Never use 2x10 or smaller, as the notches weaken the board significantly.