Use this Stair Stringer Calculator to plan equal risers, tread cuts, total run, stair angle and geometric stringer length from your finished-floor rise. Enter US or metric measurements, review the visual cut layout, and use the result as a planning reference before marking or cutting material.
Enter stringer dimensions
Start with finished-floor total rise. US measurements accept fractions such as 7 3/4.
Your stringer layout
Review the repeated rise/run cuts and the straight sloped flight geometry.
Transparent calculation
How the stringer geometry is calculated
The calculator first creates equal risers, then repeats the chosen tread run to determine total run, stair angle and the straight sloped flight length.
ceil(total rise ÷ max riser)total rise ÷ risersrisers − 1treads × cut runatan(total rise ÷ total run)√(total rise² + total run²)Important: the sloped length is geometric, not a guaranteed purchase length. Top/bottom cuts, bearing, connection details and structural adequacy require additional project-specific planning.
Step by step
How to use the Stair Stringer Calculator
Measure the vertical distance between the finished lower and upper floor surfaces, then enter a planning maximum riser height and the horizontal run you want for each tread. The calculator determines a whole number of equal risers and repeats the rise/run geometry across the flight.
- Measure total rise. Use finished-floor to finished-floor height whenever finish thicknesses are known.
- Choose the riser limit. The default is a model-code planning reference, not a universal local requirement.
- Choose tread run. This becomes the horizontal unit run in the geometric layout.
- Calculate. Review equal cut rise, number of treads, total run, angle and sloped length.
- Verify stock and construction details separately. Real stringer boards need allowances for top/bottom details, bearing, notches and connections.
For basic overall stair geometry rather than stringer-focused layout, use the Stair Calculator.
Read your result
What each stringer result means
Cut rise
The equal vertical rise assigned to each step after total rise is divided by the whole number of risers.
Cut run
The horizontal unit run you entered for each tread. This is the repeated run dimension in the geometric layout.
Number of treads
For a simple straight flight between two floors, this tool uses one fewer tread than risers because the upper floor is the final walking surface.
Total run
The number of treads multiplied by the chosen cut run.
Stair angle
The angle of the overall rise/run envelope, using total rise and total run. It describes flight geometry rather than code approval.
Geometric stringer length
The straight sloped distance from bottom to top of the calculated flight. Actual stock length normally requires extra planning allowance.
Worked example
Example: stringer layout for a 9 ft total rise
With a 108 in total rise, a 7¾ in maximum riser setting and a 10 in unit run, the calculator selects 14 equal risers. That produces 13 treads.
ceil(108 ÷ 7.75) = 14108 ÷ 14 ≈ 7.714 in13 × 10 = 130 in√(108² + 130²) ≈ 169 inThe sloped flight is roughly 14 ft 1 in long at about 39.7°. That is the geometry line only; a real stringer board should not be cut or purchased solely from that one length value.
Measure and mark carefully
Stringer layout tips
- Use one consistent finished-floor total rise for the flight.
- Keep repeated riser and tread dimensions consistent across the layout.
- Confirm that the total run fits the available horizontal space before cutting material.
- Remember that tread thickness, top attachment and bottom bearing can affect actual cut details.
- Do not use geometric sloped length alone to judge stringer strength or notch adequacy.
Know the limits
Assumptions and limitations
This calculator models a straight stair flight with equal risers and equal tread runs. It does not calculate structural stringer capacity, minimum remaining wood below notches, species/grade requirements, stringer spacing, fasteners, connectors, bearing, landing framing, top/bottom cut adjustments, headroom, guards or handrails.
The tool is therefore useful for planning repeated rise/run geometry, not for replacing construction drawings, manufacturer instructions, engineering or the requirements adopted by the project jurisdiction.
Planning reference
Why the default is 7¾ in rise and 10 in run
The default US settings match the 2021 International Residential Code model-code values in Sections R311.7.5.1 and R311.7.5.2 for the stair conditions covered by those sections: a riser not more than 7¾ in and a tread depth not less than 10 in. Local jurisdictions can adopt different editions or amendments, and some stair types have different rules.
BuildCalcForge therefore treats these values as editable planning references, not as a universal pass/fail checker.
International Code Council — 2021 IRC, Chapter 3 ↗Common questions
Stair Stringer Calculator FAQ
What does a stair stringer calculator calculate?
This tool calculates the repeated rise/run geometry of a straight stair flight, including equal riser height, tread count, total run, angle and the straight sloped length of the flight.
Is stringer length the same as the board length I should buy?
No. The geometric stringer length is the straight diagonal distance of the flight. Real stock length needs extra allowance for top and bottom details, bearing, cuts and site conditions.
Can I use 7 3/4 in as the maximum riser?
You can use it as a planning input. It matches the 2021 IRC model-code maximum for the stair conditions covered by R311.7.5.1, but the code adopted where you build can differ.
Why is the number of treads one less than the number of risers?
For the simple floor-to-floor straight-flight model used here, the upper floor is treated as the final walking surface, so there is one fewer tread than risers.
Does this calculate how many stringers my stair needs?
No. Stringer quantity and spacing depend on structural design, material, tread system, loads and applicable requirements. This tool intentionally does not prescribe that structural decision.
Can I use metric measurements?
Yes. Switch to Metric to enter total rise, riser limit, tread run and optional board length in millimeters.
Sources & methodology
How this calculator is checked
The calculator uses standard right-triangle stair geometry, keeps mathematical calculation separate from construction approval, and shows the assumptions behind the output.