Stair Calculator
Create a preliminary straight-flight stair layout. The calculator divides total rise into equal risers and reports treads, horizontal run, angle, and sloped span.
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View all saved project estimatesWhat does the stair calculator calculate?
Divide total rise by the maximum permitted riser height and round up to a whole riser count. Divide rise again for equal actual risers. A typical floor-to-floor flight has one fewer tread than risers. Verify geometry, landings, headroom, guards, handrails, and code locally.
Equal stair risers and straight-flight run
Rounding the initial quotient up keeps equal risers at or below the entered maximum. The floor-to-floor model uses one fewer tread than risers and multiplies treads by selected run.
How to measure for an accurate estimate
- Measure total rise vertically from lower finished floor to upper finished floor.
- Include final flooring thicknesses because small changes affect riser uniformity.
- Measure available horizontal space to finished obstructions and required landings.
- Field-check headroom, width, nosing, handrail, guard, door, and landing conditions.
Nine-foot floor-to-floor stair
Total rise is 108 inches, maximum riser is 7.75 inches, and tread run is 10 inches.
108 ÷ 7.75 rounds up to 14 risers at 7.714 inches; 13 treads create a 130-inch run.Before you purchase material
- Obtain local code requirements and permits before final layout or material cutting.
- Use graded structural lumber or an approved stair system sized for the design and span.
- Plan connectors, blocking, landings, guards, handrails, finishes, and lighting together.
- Build from one verified layout so every finished riser remains within permitted variation.
Common questions
How many steps do I need for a 9-foot rise?
A 108-inch rise divided by a 7.75-inch maximum requires 14 equal risers, each about 7.714 inches. In a typical floor-to-floor flight that produces 13 treads, but landing and local-code conditions can change the layout.
Why are there fewer treads than risers?
In a floor-to-floor flight, the upper finished floor serves as the surface reached by the final riser, so a separate tread is not added there. Exterior steps or flights ending differently may need another interpretation.
What is the maximum stair riser height?
Requirements depend on adopted code, occupancy, stair type, and jurisdiction. The 7.75-inch default is a common residential model-code value, not universal permission. Confirm the locally adopted edition, amendments, and project conditions before laying out stairs.
Can I use the calculated slope span as stringer length?
Use it only as a geometric reference. A cut stringer needs extra material for end cuts and must satisfy structural depth, bearing, attachment, species, grade, and span requirements. Have the final stringer design checked professionally.
Sources and reference standards
- International Code Council — 2024 International Residential CodePrimary model-code source for residential foundations, reinforcement, masonry, and stair safety requirements.
See every citation and the calculators that use it in the calculator source index.
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