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🪜 Stair Calculator

Calculate rise, run, and number of steps for code-compliant stairs. Ensure your stairs meet building code requirements.

Quick Formula​

Total Rise​

Total Rise = Upper Floor Height - Lower Floor Height

Number of Steps​

Number of Steps = Total Rise ÷ Desired Rise per Step

Individual Rise​

Rise per Step = Total Rise ÷ Number of Steps

Run (Tread Depth)​

Run = Number of Steps × Tread Depth

Building Code Requirements​

International Building Code (IBC)​

RequirementMinimumMaximumNotes
Rise4"7"Height of each step
Run11"—Tread depth
Headroom6'8"—Clear height above
Width36"—Minimum width
Handrail height34"38"Above tread nosing

Common Calculations​

Example 1: Standard Residential​

Given:

  • Floor to floor height: 9 feet (108 inches)
  • Desired rise: 7 inches

Calculation:

  • Total rise: 108 inches
  • Number of steps: 108 ÷ 7 = 15.43 → 16 steps
  • Actual rise: 108 ÷ 16 = 6.75 inches per step
  • Run (11" treads): 16 × 11 = 176 inches (14'8")

Example 2: Commercial Stairs​

Given:

  • Floor to floor height: 10 feet (120 inches)
  • Desired rise: 7 inches

Calculation:

  • Total rise: 120 inches
  • Number of steps: 120 ÷ 7 = 17.14 → 17 steps
  • Actual rise: 120 ÷ 17 = 7.06 inches per step
  • Run (11" treads): 17 × 11 = 187 inches (15'7")

Rise & Run Relationship​

The 2R + T Formula​

For comfortable stairs:

2 × Rise + Run = 24-25 inches

Example:

  • Rise: 7 inches
  • 2R = 14 inches
  • Run = 25 - 14 = 11 inches

Stair Types​

Straight Run​

  • Simplest - Single straight flight
  • Space efficient - Minimal footprint
  • Best for: Residential, small spaces

L-Shaped (90°)​

  • Landing - 90-degree turn with landing
  • More space - Requires more floor area
  • Best for: Medium spaces, better flow

U-Shaped (180°)​

  • Two flights - 180-degree turn
  • Most space - Requires significant area
  • Best for: Large spaces, grand entrances

Landing Requirements​

When Required​

  • Top and bottom - Always required
  • Every 12 feet - Maximum rise between landings
  • At turns - Required for L/U-shaped stairs

Landing Size​

  • Minimum width - Same as stair width
  • Minimum depth - 36 inches (same as width)

Handrail Requirements​

Height​

  • 34-38 inches - Above tread nosing
  • Consistent - Same height throughout

Continuity​

  • Continuous - Uninterrupted along flight
  • Returns - Return to wall at ends
  • Extensions - Extend 12" beyond top/bottom riser

Common Mistakes​

MistakeProblemSolution
Rise too highUncomfortable, code violationKeep under 7"
Run too shortDangerous, code violationMinimum 11"
Inconsistent riseTripping hazardAll rises must be equal
No landingCode violationAdd landing every 12' rise
Wrong handrail heightCode violation34-38" above nosing

Quick Reference​

Standard Dimensions​

ApplicationRiseRunNotes
Residential7"11"Standard
Commercial7"11"Standard
Outdoor6-7"12-14"Can be deeper
Basement7-8"9-10"Space constrained
Code Compliance

Stairs that don't meet code can result in failed inspections, rework, and safety hazards. Always check local building codes.