Calculate stair dimensions, number of steps, rise, run, and materials needed for your staircase project.
Stair Calculations:
Building Code Status: Compliant with IRC standards
Number of Steps: 14 steps
Step Rise: 7.71 inches
Step Run (Tread Depth): 10.0 inches
Stringer Length: 155.5 inches (12.96 feet)
Stair Angle: 37.6 degrees
Headroom Required: 80 inches minimum
Materials Needed:
Stringers: 3 pieces of 2x12 lumber
Treads: 13 treads required
Tread Material: 32.5 square feet
Lumber Cost: $58.50
Tread Cost: $276.25
Total Material Cost: $334.75
Stair Geometry Optimization & Code Compliance Guide
Core Relationships
- Risers = round(TotalRise ÷ IdealRise) (iterate until ≤7.75")
- Treads = Risers − 1
- Run per Tread = TotalRun ÷ Treads
- Stringer Length = √(TotalRise² + TotalRun²)
- Comfort Band: Rise + Run = 17.5–18.25"
Compliance Snapshot (IRC)
- Max rise 7.75" • Min run 10" • Min width 36" • Headroom ≥ 80"
- Variation (largest − smallest) riser/tread ≤ 3/8"
- Handrail required ≥ 4 risers
Stringer Engineering
- 2×12 SPF or better, min 5" throat after notching
- Span > 36" width → 3 stringers; hardwood treads may allow wider spacing if manufacturer rated
- Fasten top to ledger / hanger; bear bottom on solid support
Failure Signals
- Creaking → loose tread fasteners / deflection
- Excess bounce → under‑spaced stringers
- Uneven rise feeling → layout mis‑calc (re‑verify finish floor thickness)
Material Choices
- Interior: Pine stringers + hardwood treads / engineered caps
- Exterior: PT lumber + composite or treated treads
- Modern: Steel mono stringer + engineered panels (verify deflection)
Layout Tips
- Story pole for cumulative riser check
- Mark plumb / level lines on square with rise/run stair gauges
- Pre‑seal cut stringers (exterior)
Quick FAQ
- Bottom/toplevel mismatch? Adjust first/last tread with finish thickness accounted.
- Open risers? Opening < 4" sphere per code.
- Notch depth? Maintain ≥ 5" solid material for structural integrity.
Action Tip: Validate rise/run after flooring install dry‑fit to avoid code redos.