Stair Calculator: Calculate Rise, Run, Steps, Stringer Length & Building Code Compliance

  • Adam
  • November 5, 2025

Free stair calculator for architects, builders, and DIY projects. Calculate stair dimensions, building code compliance, and verify handrail requirements.

Stair Calculator

Calculate Stairs: Rise, Run, Steps, Stringer Length & Building Code Compliance

📏 Pro Tips for Accurate Stair Calculations: Measure total rise from finished floor to finished floor (including flooring thickness). Calculate from top of last riser to top of final floor. Always verify local building codes before construction. Consistent rise is critical for safety (prevents trips). Test calculations with mockup or template first.

Basic Stair Calculator

Formula:
Number of Steps = Total Rise ÷ Rise per Step
Total Run = Run × (Number of Steps - 1)
Stringer Length = √(Total Run² + Total Rise²)
Angle = arctan(Total Rise ÷ Total Run)
✅ Stair Calculation Results:

Comprehensive Stair Calculator

✅ Comprehensive Results:

Building Code Compliance Checker

Standard Building Code Requirements:

Max Rise: 7.75" (19.7 cm) | Min Run: 10" (25.4 cm) | Min Width: 36" (91.4 cm) | Min Headroom: 6'8" (203 cm) | Handrail Height: 34-38" (86-97 cm)

📋 Building Code Compliance Report:
🔨 Stair Terminology & Components
Rise/Riser:

Vertical height of one step (from top of one tread to top of next tread). Building code maximum: 7.75 inches (19.7 cm). Consistent rise is critical for safety.

Run/Tread:

Horizontal depth of step (outer edge to edge, including nosing if present). Building code minimum: 10 inches (25.4 cm). Wider runs (11-12 inches) are more comfortable.

Tread:

Physical step surface you walk on. Includes nosing (protrusion at edge). Length measured from outer edge of step. Minimum nosing: 0.75 inches (1.9 cm). Maximum: 1.25 inches (3.2 cm).

Nosing:

Part of tread that protrudes beyond riser. Provides extra space for foot placement. Improves safety by preventing heel striking next riser.

Stringer:

Diagonal structural member supporting treads and risers. Usually three per staircase: one on each side and one in middle. Can be cut to shape of each step or routed.

Headroom:

Vertical clearance from tread to ceiling above. Building code minimum: 6 feet 8 inches (203 cm). Measured at nosing edge.

Handrail & Guard:

Handrail: railing to hold when ascending/descending. Guard: protective barrier. Required for stairs over 30 inches rise. Handrail height: 34-38 inches (86-97 cm) from top of tread.

Stair Width:

Measured edge to edge of each tread side. Building code minimum: 36 inches (91.4 cm). Measured perpendicular to tread length.

📋 Building Code Requirements Summary
Component Requirement Metric Notes
Rise (max) 7.75 inches 19.7 cm Step height, safety critical
Run (min) 10 inches 25.4 cm Tread depth
Nosing (min) 0.75 inches 1.9 cm Tread overhang
Nosing (max) 1.25 inches 3.2 cm Tread overhang
Width (min) 36 inches 91.4 cm Edge to edge
Headroom (min) 6'8" 203 cm Clearance to ceiling
Handrail Height 34-38 inches 86-97 cm From top of tread
Handrail Diameter 1.25-2.675 inches 3.18-6.79 cm Graspable section
2 to 1 Rule 2R + Run = 24-26" 61-66 cm Comfort ratio
Rise Total + Run Variance ≤ 3/8 inch ≤ 0.95 cm All steps must be uniform
📐 Fraction to Decimal Conversion
16ths 8ths 4ths 2nds Decimal
1/16 0.0625
2/16 1/8 0.125
3/16 0.1875
4/16 2/8 1/4 0.25
5/16 0.3125
6/16 3/8 0.375
7/16 0.4375
8/16 4/8 2/4 1/2 0.5
9/16 0.5625
10/16 5/8 0.625
11/16 0.6875
12/16 6/8 3/4 0.75
13/16 0.8125
14/16 7/8 0.875
15/16 0.9375
16/16 8/8 4/4 2/2 1
❓ Frequently Asked Questions
What is the ideal stair rise and run ratio for comfort? +
The 2 to 1 rule: 2 × Rise + Run = 24-26 inches. Example: 2(7.5) + 11 = 26 inches (comfortable). Stairs following this rule feel natural and safe. Steeper stairs (large rise, small run) feel awkward; shallower stairs (small rise, large run) are tiring.
How do I calculate stringer length? +
Use Pythagorean theorem: Stringer = √(Total Run² + Total Rise²). Example: √(120² + 100²) = √25,600 ≈ 160 inches. This is the diagonal length of the structural support beam.
Why is consistent rise height so important? +
Inconsistent steps cause trips and falls. Your foot expects uniform height; variation shocks muscles and balance. Building code requires all risers uniform (variance ≤ 3/8 inch). Consistency is more important than specific dimension.
What is headroom and why is 6'8" minimum? +
Headroom: vertical clearance from step to ceiling. 6'8" (203 cm) allows tall people to use stairs safely without ducking. Measured at nosing edge. Insufficient headroom is hazardous and code violation.
When are handrails required? +
Required for stairs with total rise over 30 inches (76.2 cm). Handrail height: 34-38 inches (86-97 cm) from top of tread. Diameter: 1.25-2.675 inches. Improves safety and assists people with mobility challenges.
What is the difference between standard and flush mount? +
Standard mount: stringer attached to side of staircase (visible from below). Flush mount: stringer tucked into wall or concealed (stairs appear to float). Flush mount is more aesthetic but requires more complex construction and structural support.
How do I account for landing or floor thickness? +
Always measure total rise from finished floor to finished floor (including any flooring material). For second floor, measure to top surface (not subfloor). Landing thicknesses affect calculations. Off-by-one-step problems usually result from not accounting for floor thickness.
What is the stair angle and typical range? +
Stair angle: arctan(Total Rise ÷ Total Run). Typical range: 30-35° for comfortable indoor stairs, up to 45° for steep stairs. Below 30° wastes space; above 45° is exhausting. 30-35° is ideal for residential stairs.

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