Stair stringer calculator
Once you know riser height and tread depth, the stringer is the hypotenuse you cut from. This page focuses on stringer length and how many stringers to buy — not the full stair “feel” math on the general stair page. It will not grade lumber for you or stamp a landing design.
+0% so you don't come up short
Planning estimate only — not engineered framing. Check throat depth after notches.
When to use
Cutting 2×12 stringers for a deck; estimating board feet of stringer stock; checking whether a single piece of lumber is long enough before you scarf.
When not to
Manufactured stair systems with stamped layouts. Notched vs solid stringer engineering — ask local practice / engineer for tall or heavy loads.
Assumptions
Stringer length ≈ √(total_rise² + total_run²) for the carriage line (simplified). Number of stringers is an input (often 3 for residential deck widths). Waste for miscuts default separate.
Worked examples
Example 1
rise 105 in, run 136.5 in
→ length ≈ 172 in (~14.3 ft) — buy 16 ft stock if that is what the aisle has
Crown and defects eat usable length.
Example 2
rise 56 in, run 73.5 in, 3 stringers
→ length ≈ 92 in; three pieces from 10 ft stock with room to square ends
How it calculates
Take rise and run from the stair planner, compute the hypotenuse, multiply by stringer count.
- Enter total rise and total run in inches (from the stair calculator outputs).
- Set how many stringers you need.
- Optional cut waste; read length and piece count.
stringer length ≈ √(rise² + run²) stock count = stringers needed × (1 + cut waste%)
Common traps
- Throat depth after notching — a long hypotenuse still fails if notches leave a skinny throat.
- Top/bottom seating cuts add to the story beyond pure Pythagorean length.
- Pressure-treated vs cedar is species choice; length math is the same.
- Sharing one layout stringer as a template beats measuring each independently.
Next tool
Riser/tread planning first → stair calculator.
Deck board count → deck board calculator.
FAQ
Roughly the hypotenuse of total rise and total run, plus seating cuts.
Related
Estimate only — not a contractor bid or engineered takeoff. Confirm bag yields and local codes before you pour or order.