Stairs Calculator
Find stair risers, true riser height, total run, and straight stringer line from floor rise and a chosen tread size for planning.
Vertical distance from lower floor to upper floor.
Result
14 risers
A 108 in total rise needs about 14 risers at 7.71 in each
Quick Answer
A stairs calculator rounds total rise divided by the target riser height to a whole riser count, then finds the true riser height. With 108 inches of rise, a 7.5-inch target, and 10-inch treads, it gives 14 risers, 7.71-inch rises, 130 inches of run, and a 169.01-inch stringer line.
How A Stairs Calculator Works From Rise To Stringer
This tool turns floor-to-floor rise into an early geometry check for a straight stair. It divides the full rise by the target riser height and rounds to a whole count because a stair cannot have part of a riser. The true riser height then comes from dividing total rise by that count. A straight flight has one fewer built tread than risers because the upper floor acts as the final step face. Tread depth times tread count gives total run. Rise and run form a right triangle, whose long side gives the basic stringer line. This math helps test whether a stair may fit, but it does not check headroom, landings, nosing, rails, stringer cuts, board strength, or code compliance.
The Stair Geometry Formula For Risers, Run And Length
All inputs use inches. Rounding to a whole riser count changes the actual height of each rise, so check that recalculated value before using the remaining geometry.
- Riser count = round(total rise ÷ target riser height).
- True riser height = total rise ÷ riser count.
- Tread count = riser count − 1.
- Total run = tread depth × tread count.
- Stringer line = √(total rise² + total run²).
The output describes nominal straight-flight geometry before finish and connection details.
Local requirements may also address dimension limits, variation, nosing, landings, headroom, clear width, handrails, guards, structural capacity, fire safety, and accessibility.
Stairs Calculator Steps For Rise, Treads And Stringer
Inputs
- Total rise: enter the full finished-floor-to-finished-floor rise in inches.
- Desired riser height: enter the target rise for each step in inches.
- Tread depth: enter the level depth of each tread in inches.
Steps
- Measure from one finished floor to the next.
- Enter the target riser height.
- Enter the tread depth.
- Read the whole riser count and true rise.
- Check the total run and stringer line.
Stair Example With Riser Height And Stringer Working
108 in total rise, 7.5 in target riser height, and 10 in tread depth.
- Find riser count: 108 in ÷ 7.5 in = 14.4, rounded to 14 risers.
- Find true riser height: 108 in ÷ 14 = 7.71429 in.
- Find tread count: 14 risers − 1 = 13 treads.
- Find total run: 13 × 10 in = 130 in.
- Find stringer line: √(108² + 130²) = √28,564 = 169.00888 in.
14 risers, 7.71 in true riser height, 130 in total run, and 169.01 in stringer line, rounded to two decimal places.
When A Stair Geometry Estimate Supports Early Planning
Use the calculation to test a straight stair and the floor space it may need. Check local code, headroom, landings, nosing, rails, guards, and load details before work.
Field measurements matter because floor finishes, framing settlement, concrete variation, and measurement error can alter the finished rise. A cumulative difference can create uneven risers or a final step outside the local tolerance.
For another right-triangle planning tool, see the rafter calculator. More tools are listed on the construction calculators hub.
Assumptions
- The stair is one straight flight.
- Rise is measured between finished floors.
- The top floor acts as the last tread face.
- Each rise and tread has one set size.
- Stringer line is the plain rise-and-run diagonal.
Limitations
- The result does not prove code compliance.
- Nosing, tread build, landings, and headroom are not calculated.
- Stringer cuts, bearing, board size, and loads are not checked.
- Turned, winder, spiral, and split stairs need different plans.
- Floor finishes and site dimensions can change the final stair.
In Practice
The key error is checking the target rise but not the true rise after rounding. A whole riser count changes every step. Check the final rise and tread against the code used for the job before marking or cutting a stringer.
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Open the CalculatorRelated Guides
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Frequently Asked Questions About Stairway Geometry
Why Is There One Fewer Tread Than Risers?
A straight stair often has one fewer built tread because the upper floor is the final step face. With 14 risers, this calculation uses 13 treads. A different top or landing detail may require another count.
Why Does Actual Riser Height Change After Rounding?
The rounded riser count must divide the full floor-to-floor rise evenly. In the example, 108 ÷ 7.5 = 14.4, which rounds to 14. Dividing 108 by 14 then gives 7.71429 inches for each rise rather than the 7.5-inch target.
Does The Stringer Length Include The Final Cuts?
The stringer line is the plain diagonal formed by full rise and run. It does not add stock for top cuts, seat cuts, bearing, trim, or site fitting. Use it as a length check, then follow the stair plan for cut marks.
Are The Results Automatically Code Compliant?
The results are not automatically compliant with any local building code. Stair limits vary with the adopted code, location, use, and stair type. Check the requirements in force for the job.
Can This Calculator Design Landings Or Winder Stairs?
This straight-stair calculator does not design landings, winders, turns, or spiral stairs. Those forms require more dimensions and safety checks than basic rise-and-run geometry provides.
Sources
Last updated: . Reviewed for accuracy against the formula shown above.