Stair Calculator: Rise, Run & Stringer Layout
Enter the total rise to calculate riser count, actual riser height, tread intervals, total run, stair angle, and straight-stair slope geometry. The live diagram updates as you work.
Stair dimensions
V1 calculates a straight flight where the upper floor or deck is the final walking surface.
Advanced reference inputs
108, 108.5, 108 1/2, 9' 0", 9' 0 1/2", 7-3/4.
Layout results
Enter a total rise to begin.
Live side elevation
About the stringer measurement
The slope-line result follows the repeating stair pitch from the first tread level to the upper floor edge. Final stringer stock length depends on the top and bottom termination details, bearing, and field cuts. Verify the layout on the actual board before cutting.
Interested in learning professional carpentry skills?
Stair layout is one of many framing skills carpenters learn to use in real projects.
How this stair calculator works
The calculator divides your finished-surface total rise into a whole number of equal risers. In this V1 layout, the upper floor or deck is treated as the final walking surface, so a straight flight has one fewer tread interval than risers.
Riser count
risers = ceiling(total rise ÷ max riser)
Then the actual riser is recalculated so every mathematical rise is equal.
Total run
total run = tread intervals × tread depth
With the upper floor as the final walking surface, tread intervals = risers - 1.
Stair angle
angle = atan(actual riser ÷ tread depth)
The angle uses the repeating rise/run pair. It is not calculated by mixing every rise with one fewer horizontal going.
What the code reference notices mean
The calculator uses the 2024 International Residential Code (IRC) as a current U.S. model-code reference for common residential stair dimensions. Model codes are adopted and amended by jurisdictions, so the notices are deliberately advisory rather than a pass/fail code checker.
- Riser reference: maximum 7 3/4 inches.
- Tread reference: minimum 10 inches.
- Headroom reference: minimum 6 feet 8 inches.
- Single-flight vertical-rise reference: maximum 12 feet 7 inches between floor levels or landings.
- Handrail reference: at least one side for a flight with four or more risers.
Deck mode also compares cut-stringer geometry with selected stair details in the American Wood Council's DCA 6 Prescriptive Residential Wood Deck Construction Guide. That guide has a specific attached-residential-deck scope and is based on the 2015 IRC, so those notices are separately labeled.
Measure total rise finish to finish
For the cleanest geometry, measure vertically from the finished lower walking surface to the finished upper walking surface. If flooring or decking is not installed yet, account for the finished-surface elevations before relying on the calculated riser height.
Tread depth in this tool means the horizontal going between adjacent tread leading-edge planes. The physical tread board can be wider because nosing projection is a separate detail.
Stair calculator questions
Why are there fewer tread intervals than risers?
In this V1 configuration, the upper floor or deck is the final walking surface. A flight with 14 risers therefore has 13 horizontal tread intervals before reaching the upper surface.
Is the slope-line length the exact stringer board length?
No. It describes the repeated stair slope between the first tread level and upper floor edge. The actual board-stock requirement depends on the top and bottom termination cuts, bearing details, and field trimming.
Does a reference notice mean the stair fails code?
No. It means the entered or calculated value falls outside a benchmark shown in the referenced model code or deck guide. Local adoption and amendments control what applies to a real project.
Can this calculator design L-shaped, U-shaped, winder, or spiral stairs?
No. V1 is deliberately limited to a single straight flight. Turning stairs and winders need additional geometry and code checks that are outside this tool's current scope.
Primary references
Calculator logic reviewed August 13, 2026. Model-code reference: 2024 IRC. Deck reference: AWC DCA 6, 2015 IRC edition.