Staircase Calculator
Calculate stair riser height, number of steps, total run, stringer board length, and angle.
Stair Dimensions & Code Constraints
Staircase Profile Schematic
Framing & Construction Cut Specs
About this tool
How to use it
- Select your unit system (Imperial Inches or Metric Centimeters).
- Enter Total Vertical Rise measured finished floor to finished floor.
- Optionally fix the exact Number of Steps if your design already calls for a specific riser count — the calculator then works out the resulting riser height and checks it against code, instead of deriving the step count for you.
- Adjust Target Riser Height (standard ~7.25" / 18.5 cm) and Tread Depth (min 10" / 25.4 cm) — used to auto-calculate the step count whenever the override above is left blank.
- Review the live SVG profile diagram illustrating stringer hypotenuse, step count, and angle of incline.
- Inspect the framing cut specifications (exact riser fraction, total horizontal footprint, and lumber board length needed).
Why it matters
Building stairs without precise calculations leads to failed building code inspections, uneven step heights (a major trip hazard), or running out of horizontal space. Using residential International Residential Code (IRC) constraints ensures safe, ergonomic stairs that pass municipal inspection on the first try.
When to use it
Use this calculator before cutting 2x12 stair stringers for indoor basement stairs, second-story additions, outdoor wooden decks, or remodeling entryway steps.
Good to know
Always measure Total Rise from FINISHED lower floor to FINISHED upper floor (accounting for tile, carpet pad, and underlayment). IRC building code mandates maximum riser height of 7 3/4 inches (197 mm) and minimum tread depth of 10 inches (254 mm).
Common questions
What is the maximum riser height by building code?
Under the International Residential Code (IRC section R311.7.5.1), the maximum riser height for residential stairs is 7 3/4 inches (197 mm). Commercial buildings (IBC) require a maximum riser height of 7.00 inches (178 mm).
What is the 2R + T rule (Blondel's formula)?
Blondel's formula states that two risers plus one tread (2 × Riser + Tread) should equal between 24 and 25 inches (600 to 640 mm). This matches the natural human walking stride for maximum climbing comfort and minimal fatigue.
How do I calculate total run?
Total run is calculated by multiplying the number of treads by the tread depth. Because the top finished floor acts as the final landing, a staircase always has one less tread than risers (Number of Treads = Number of Risers - 1).
What size lumber is used for stair stringers?
Stair stringers are almost universally cut from structural 2x12 dimensional lumber (or engineered LVL lumber). After cutting the triangular notches, at least 3.5 inches of solid wood 'throat' must remain along the bottom edge for structural integrity.
What is the minimum headroom clearance required?
The International Residential Code requires a minimum headroom clearance of 6 feet 8 inches (80 inches / 203 cm) measured vertically from the leading edge of the tread stair nosing to the ceiling overhead.