Stair Stringer Cut Calculator
Get exact layout and cut lines for stair stringers. Use our free cut list generator.
Calculated Results
⚠ Disclaimer: This calculator is a planning aid. Always verify results against your local building codes and regulations before construction. Consult a licensed professional for structural requirements.
What is Stair Stringer Cut Calculator
A stair stringer cut calculator shows you where to mark and cut a 2x12 lumber board to make stair stringers. It provides step-by-step layout points. Carpenters use it to avoid expensive cutting mistakes.
The calculator lists framing square layout points. It also reminds you to adjust the bottom cut for tread thickness.
Stair Stringer Cut Calculator Formula
The Pythagorean theorem applied to stair stringer construction
A stair stringer formula calculates the diagonal length of the stringer board using two measurements: total rise and total run. Total rise is the vertical height between finished floors. Total run is the horizontal distance across all treads.
L = √(Rise² + Run²) θ = arctan(Rise ÷ Run) The stair angle determines comfort and code compliance. The International Residential Code (IRC) limits residential stair angles to 30°–37° for safe foot placement. Stairs steeper than 37° feel uncomfortable and violate most building codes. Stairs shallower than 30° waste floor space without improving safety.
Example: Calculate Stair Stringer Length
A staircase with 98 inches of total rise and 120 inches of total run:
- Stringer Length = √(98² + 120²) = √(9604 + 14400) = √24004 ≈ 154.9 inches
- Stair Angle = arctan(98 ÷ 120) = 39.2° (exceeds IRC max of 37°)
This staircase needs more total run to reduce the stair angle below the 37° IRC limit. Increasing total run to 136 inches gives an angle of 35.8°.
Rise and Run: The Two Inputs
Rise is the vertical height of each individual step (riser height). Run is the horizontal depth of each step (tread depth). The stair stringer formula uses the total values — the sum of all individual risers and all individual treads — to compute the full stringer board length.
Stair building tools like a framing square use the individual rise and run to mark notch positions along the stringer. The stringer angle, kickback angle, and notch depth all derive from this same rise-and-run relationship.
L = √(R² + D²) L = stringer length · R = total rise · D = total run
How to Calculate Stair Stringers
Five steps from measurement to cut-ready stringer layout
Measure Total Rise
Measure the vertical distance from the lower finished floor to the upper finished floor. Use a level and tape measure. Total rise determines every other stair stringer calculation — a ½-inch error on total rise spreads unevenly across all risers.
Count the Risers
Divide total rise by a target riser height between 7 and 7.5 inches. Round to the nearest whole number. A total rise of 98 inches divided by 7.5 equals 13.07, which rounds to 13 risers. The actual riser height becomes 98 ÷ 13 = 7.538 inches.
Set Tread Depth and Total Run
Minimum tread depth is 10 inches per the International Residential Code (IRC) R311.7. Number of treads equals risers minus one, because the top riser lands directly on the upper floor. Total run equals tread depth multiplied by the number of treads.
Check Building Code Compliance
Maximum riser height: 7.75 inches (IRC R311.7). Minimum tread depth: 10 inches. Apply the comfort rule: riser height plus tread depth should sum to 17–18 inches for optimal walking rhythm. Verify the stair angle stays between 30° and 37°.
Mark and Cut the Stringer
Set the framing square with riser height on one leg and tread depth on the other. Align the framing square to a 2×12 lumber board and trace each step notch along the stringer layout. Subtract one tread thickness from the bottom riser height to keep all finished steps uniform after tread board installation.
Hover a step to highlight it on the stringer diagram
Stairs with Risers
Open-riser versus closed-riser staircase design comparison
Stairs with risers use vertical boards between each tread to close the gap between steps. Open-riser stairs omit these boards, leaving the space between treads visible. Both styles affect staircase design, building code requirements, and stringer layout.
Closed-Riser Stairs
Closed-riser stairs are the standard for interior residential construction. The riser board provides a finished appearance, blocks debris from falling through, and adds lateral stiffness to the stair stringer. Maximum riser height remains 7.75 inches per IRC R311.7 regardless of whether the riser is open or closed.
Open-Riser Stairs
Open-riser stairs are common on deck stairs and modern interior designs. Building codes limit the gap between treads to 4 inches maximum on open-riser stairs to prevent small children from passing through. Deck stair lighting integrates easily into open-riser designs since the light mounts under each tread nosing.
Stringer Layout Differences
Both open and closed riser stairs use the same stair stringer formula for calculating rise and run. The stringer notching pattern stays identical. The difference is material: closed-riser stairs add one riser board per step to the material estimate. Wooden stringers support both styles; steel stringers often use open-riser designs for industrial staircase applications.
Frequently Asked Questions
How do you cut a stair stringer?
Mark notches using a square, cut the straight lines with a circular saw, and finish the inside corners with a hand saw.
What saw is best for cutting stringers?
A circular saw is best for the long cuts, and a hand saw or jigsaw is used to finish the corner cuts.
Do you cut the top and bottom of a stringer differently?
Yes, cut the bottom shorter by the tread thickness, and cut the top to fit your chosen mount type.