Stair Calculator
Calculate staircase dimensions including rise, run, number of steps, and stringer length with building code compliance.
What is the ideal rise and run for stairs?
Building codes and comfort standards: Rise (vertical step height): 7-7.75 inches ideal, 7.75 inches maximum by code. Run (tread depth): 10-11 inches minimum, 11 inches ideal. Total formula: 2×Rise + Run = 24-25 inches (comfortable stride). Example: 7.5 inches rise + 10 inches run: 2×7.5 + 10 = 25 inches perfect. Steeper stairs (higher rise) are harder to climb, require handrails. Shallower stairs waste space but are safer, more comfortable.
How do I calculate the number of steps needed?
Formula: Number of risers = Total Rise / Ideal Rise per Step (round to nearest whole number), then recalculate: Actual Rise = Total Rise / Number of Risers. Number of treads = Risers - 1 (top riser at landing level). Example: 108 inches total rise ÷ 7.5 inches = 14.4, round to 14 risers. Actual rise = 108 ÷ 14 = 7.714 inches per step. Treads needed = 13. Never round risers down below code minimum or stairs won't reach.
What are residential building code requirements for stairs?
International Residential Code (IRC) minimums: Maximum rise: 7-3/4 inches (7.75 inches). Minimum tread: 10 inches (nosing not included). Width: 36 inches minimum clear. Headroom: 80 inches minimum vertical clearance. Handrails: Required one side if 4+ risers, both sides if 44 inches+ wide, 34-38 inches height. Uniformity: Riser variation max 3/8 inches, tread variation max 3/8 inches. Landings: Required at top/bottom, depth ≥ stair width. Always check local codes - some stricter.
How much space do stairs take up?
Total run calculation: Number of Treads × Tread Depth = Horizontal space needed. Example: 14 risers (13 treads) × 10 inches = 130 inches (10.8 feet) horizontal. Plus landings: 36 inches minimum at top and bottom. Total floor space: 10.8' + 3' + 3' = 16.8' length. Width: 36-42 inches typical. Vertical space: Total rise plus headroom (80 inches). For tight spaces, consider: L-shaped stairs with landing (saves space), spiral stairs (48-60 inches diameter), alternating tread stairs (steeper, less space).
What is the difference between risers and treads?
Riser: Vertical part of step (height), or the vertical board closing the gap. Number of risers = number of steps up. Tread: Horizontal part where you step (depth), or the board you walk on. Number of treads = risers - 1 (last riser connects to upper floor, no tread). Example: 14 risers, 13 treads for 108 inches rise. Nosing: Tread overhang (1-1.5 inches), not counted in tread depth. Open risers (no vertical board) allowed in some codes if gap <4 inches sphere.
Can I build stairs steeper than code to save space?
No for primary stairs - must meet code (max 7.75 inches rise). Exceptions allowed: Alternating tread stairs (ships ladder style, 50-70° angle) for attics, lofts, mezzanines - saves space but less safe, requires handrails. Spiral stairs (steeper, compact) allowed as secondary access. Ladders permitted for attics if not habitable space. Primary stairs to bedrooms, living areas must meet full code. Inspectors will fail non-compliant stairs. Steep stairs dangerous, reduce home value, difficult for elderly/children/moving furniture.
How do I calculate stair stringers?
Stringer (diagonal support beam) calculation: Length = √(Total Rise² + Total Run²) using Pythagorean theorem. Example: 108 inches rise, 130 inches run: √(108² + 130²) = √28,564 = 169 inches = 14.1 feet stringer length. Notches: Cut for each rise/run combination - requires precision. Typically need 3 stringers: 2 outer + 1 center support for 36 inches width. For wider stairs (48 inches+), add stringers every 16 inches. Material: 2×12 lumber standard (allows cutting without weakening). Bottom cut sits on floor, top cut attaches to header/joist.