Stair Stringer Calculator
Get the exact stringer length, throat depth, recommended board size, and a step‑by‑step cut layout with framing‑square settings — then print a full‑scale template.
Finished floor to finished floor.
Stairs Calc rounds to a whole number of equal risers and keeps them within code.
The depth you step on, not counting the nosing.
Top of the rail above the nosing line. Codes target 34–38".
A guard fills the side with your chosen infill — balusters, glass, cable, or horizontal bars. Renders live in 3D and is included in the .obj export.
Advanced inputs
Open risers leave a gap between treads — drawn live in the diagram. Some codes (ADA) require closed risers.
Steps (risers)
16
15 treads
Riser height
7 3/16"
183 mm
Tread run
11"
279 mm
Stringer length
16' 8 15/16"
5.104 m
Stair angle
33.2°
Very comfortable
Total run
13' 8 3/4"
4.185 m
Min stairwell opening
10' 11 13/16"
3.348 m
Recommended board
2x12
throat 5 1/4"
Board to buy
17' 8 15/16"
5.409 m
Comfort
Very comfortable
- Blondel pass
- Rise + Run pass
- Ideal angle pass
Cut list & framing square
Materials
| Item | Qty | Detail |
|---|---|---|
| Stringers | 3 | 2x12 cut to board length |
| Treads | 15 | tread depth 304 mm × 914 mm wide |
| Risers | 16 | riser height 183 mm × 914 mm wide |
| Fasteners | 180 | structural screws / nails (≈4 per tread-to-stringer joint) |
Framing-square settings
- Rise on tongue
- 7 3/16"
- Run on body
- 11"
- Recommended board
- 2x12
- Throat
- 5 1/4"
- Board length
- 17' 8 15/16"
- Stringers
- 3
Per-step running measurements
| Step | Cumulative rise | Cumulative run |
|---|---|---|
| 1 | 7 3/16" | 11" |
| 2 | 14 3/8" | 21 15/16" |
| 3 | 21 9/16" | 32 15/16" |
| 4 | 28 3/4" | 43 15/16" |
| 5 | 35 15/16" | 54 15/16" |
| 6 | 43 1/8" | 65 7/8" |
| 7 | 50 5/16" | 76 7/8" |
| 8 | 57 1/2" | 87 7/8" |
| 9 | 64 11/16" | 98 7/8" |
| 10 | 71 7/8" | 109 13/16" |
| 11 | 79 1/16" | 120 13/16" |
| 12 | 86 1/4" | 131 13/16" |
| 13 | 93 7/16" | 142 13/16" |
| 14 | 100 5/8" | 153 3/4" |
| 15 | 107 13/16" | 164 3/4" |
| 16 | 115" | 175 3/4" |
Cut the bottom riser shorter by 1" so every finished riser stays equal.
Save & compare designs Show Hide
Save the stair you're looking at, tweak the inputs, save another, then compare them side by side — comfort, code, and key dimensions at a glance.
Estimate the cost $1,139–$1,709
| Stringers (3) | $176 |
| Treads (15) | $270 |
| Risers (16) | $144 |
| Fasteners & hardware | $25 |
| Railing | $335 |
| Labor | $475 |
Low
$1,139
Estimate
$1,424
$89/step
High
$1,709
Rough order-of-magnitude only. Lumber, fastener and labor prices swing by region and season — the low–high band reflects that spread. For a line-item breakdown with editable prices, open the stairs cost calculator.
How do you calculate stair stringer length?
A stringer is the hypotenuse of the stair triangle: length = √(total rise² + total run²). For a 9′‑7″ rise and 13′‑9″ run that is about 16′‑9″ — buy the board 12″ longer for the plumb and seat cuts. After notching, keep at least 3½″ of throat behind the cut, which usually means a 2×12.
- Stringer (example)
- 16′‑9″
- Min throat
- 3½″
- Buy extra
- 12″
- Typical board
- 2×12
How to lay out and cut a stringer
- Measure the total rise — finished floor to finished floor.
- Pick the riser count the calculator suggests, which keeps every riser equal and within code. To choose those numbers first, run the stair rise and run calculator.
- Set the framing square: put the riser height on the tongue and the run on the body, and clamp stair gauges so every step is identical.
- Mark each notch down the board, sliding the square step to step.
- Cut the drop off the bottom — shorten the first riser by one tread thickness so the finished risers stay equal.
- Test-fit one stringer, then trace it to lay out the rest so all carriages match.
What size board: 2×10 vs 2×12
After you notch a stringer, the wood left behind the cut — the throat — must stay at least 3½″ or the carriage is too weak. With a typical 11″ run and a 7″ riser, a 2×10 leaves too little throat, so Stairs Calc recommends a 2×12 for most stairs and tells you the exact throat depth for your numbers. The calculator above shows the recommended board and a full cut list with framing-square settings and per-step running marks. Building outdoors? The deck stairs calculator adds footing, post and water-shedding notes for the same stringers.
Stringer formulas
- Number of risers
N = round(total rise ÷ ideal riser)Round to the nearest whole number, then divide the rise back by N for the exact, equal riser height.
- Riser height
riser = total rise ÷ N- Treads
treads = N − 1The upper floor acts as the top step.
- Total run
total run = (N − 1) × run- Stringer length
stringer = √(total rise² + total run²)The hypotenuse of the staircase triangle (Pythagoras).
- Stair angle
angle = atan(rise ÷ run)The pitch of one step.
- Minimum stairwell opening
opening = ((floor thickness + headroom) × total run) ÷ total rise- Throat
throat = board width − (rise × run) ÷ √(rise² + run²)Keep at least 3½″ of solid wood behind the notch.
- Comfort — Blondel
2 × rise + run = 24″–25″The classic stepping-cadence rule.
- Comfort — Rise + Run
rise + run = 17″–18″- Comfort — Product
rise × run ≈ 70–75 in²
Frequently asked questions
How long should a stair stringer be?
A stringer is the hypotenuse of the stair triangle: stringer = √(total rise² + total run²). For a 2921 mm rise and 4185 mm run that's about 16′‑9″. Add roughly 12″ to the board length for the top and bottom cuts.
2x10 or 2x12 for stringers?
It comes down to the throat — the solid wood left behind the deepest notch, which should stay at least 3½″. A 2x10 only works for shallow treads; once your tread run reaches about 11″ you need a 2x12 to keep enough throat.
How many stringers do I need?
Space stringers no more than about 16″ apart. A 36″ stair needs 3 stringers; wider flights or thin treads need 4–5.
What is the "drop" on a stringer?
The drop is the amount you cut off the bottom riser — shortened by one tread thickness — so that once the treads are installed every finished riser ends up equal. Stairs Calc applies it automatically.
How do I mark stringers with a framing square?
Set the riser height on the square's tongue and the run on the body, clamp on stair gauges to lock those numbers, then step the square along the board to mark each notch.
Related stair calculators
Written by the Stairs Calc editorial team. Methodology and code references: see our methodology.
Built and maintained by builders, drafters and engineers who plan stairs for a living — every code limit is transcribed from the published standard and cited to its exact section.
Last reviewed 2026-06-20 against IRC 2021/2024
Stairs Calc gives accurate geometry and checks it against published building-code limits, but results are estimates for planning. Codes are adopted and amended locally and change over time. Always confirm dimensions against your local adopted code and a licensed professional before you build.