Stair Calculator
Calculate stair dimensions, rise, run, and materials needed for safe and comfortable staircase construction following building codes and ergonomic standards.
Stair Specifications
Material Specifications
Building Code Presets
Stair Calculations
Material Estimates
🛡️ Safety Recommendations:
- • Install proper handrails and adequate lighting
- • Use non-slip materials for treads
How to Use the Stair Calculator
To design safe and comfortable stairs:
- Choose your calculation method (total rise, individual steps, or stringer length)
- Enter the required measurements based on your selected method
- Specify material preferences and number of stringers
- Review the calculated dimensions and code compliance
- Use building code presets for standard configurations
- Check material estimates and safety recommendations
- Adjust dimensions as needed to meet building codes
Stair Design Formulas
Basic Stair Calculations
Number of Steps: Number of Steps = Total Rise ÷ Desired Rise per Step
Actual Rise: Actual Rise = Total Rise ÷ Number of Steps
Total Run: Total Run = (Number of Steps - 1) × Tread Depth
Stringer Length
Formula: Stringer Length = √(Total Rise² + Total Run²)
This uses the Pythagorean theorem to calculate the diagonal length of the stringer.
Stair Angle
Formula: Angle = arctan(Total Rise ÷ Total Run)
Optimal stair angles range from 30° to 40° for comfort and safety.
2R + T Rule
Formula: 2 × Rise + Tread = 24" to 25"
This ergonomic rule ensures comfortable step proportions for average stride length.
Example: Residential Staircase
Given:
- Total Rise: 108 inches (9 feet floor-to-floor)
- Desired comfortable rise: 7 inches per step
- Desired tread depth: 11 inches
Calculations:
- Number of Steps: 108 ÷ 7 = 15.43, round to 15 steps
- Actual Rise: 108 ÷ 15 = 7.2 inches per step
- Total Run: (15 - 1) × 11 = 154 inches
- Stringer Length: √(108² + 154²) = 188.5 inches
- Stair Angle: arctan(108 ÷ 154) = 35.1°
- 2R + T Check: (2 × 7.2) + 11 = 25.4 inches ✓
Frequently Asked Questions
What is the ideal rise and run for stairs?
For residential stairs, a 7-inch rise with an 11-inch tread is considered ideal for comfort. Commercial stairs typically use a 7-inch rise with an 11-inch minimum tread.
How many stringers do I need?
For stairs up to 30 inches wide, use 2 stringers. For 30-48 inches, use 3 stringers. Add one stringer for every additional 16 inches of width for proper support.
What is the minimum headroom required?
Most building codes require a minimum of 80 inches (6'8") of headroom measured vertically from the stair tread nosing to the ceiling above.