Stair Calculator
Calculate stair dimensions, stringers, and verify building code compliance
Calculate Stair Dimensions
Floor-to-floor height in inches
Max: 7.75" (IRC Code)
Min: 10" (IRC Code)
Min: 36" (IRC Code)
Standard: last step lands on floor. Flush: last step aligns with floor height.
Stair Calculation Results
Formula used: Steps = Total Rise ÷ Rise per Step
Total run: (Steps - 1) × Run
Stringer length: √(Total Run² + Total Rise²)
Comfort Rule Check
2 × Rise + Run: 0.0in
Target: in (±1")
Building Code Compliance (IRC 2015)
Example Calculation
Typical Residential Stair
Total Rise: 108 inches (9 feet floor-to-floor)
Desired Rise per Step: 7.2 inches
Run per Step: 11 inches
Mount Type: Standard
Results
Number of Steps = 108 ÷ 7.2 = 15 steps
Actual Rise = 108 ÷ 15 = 7.2" per step
Total Run = (15-1) × 11 = 154"
Stringer Length = √(154² + 108²) = 188.5"
Comfort Check: 2 × 7.2 + 11 = 25.4" ✅
IRC Building Code (2015)
Rise Requirements
Max 7.75" (196mm) per step
Max 147" (3734mm) total between landings
Run Requirements
Min 10" (254mm) per step
Measured horizontally
Safety Features
Min 36" (914mm) width
Handrails required for 4+ steps
Stair Design Tips
Keep all steps uniform in height and depth
Follow 2×rise + run ≈ 25" comfort rule
Install handrails 34-38" above step nosing
Maintain 6'8" minimum headroom clearance
Consider local building codes for permits
Understanding Stair Calculations
Key Measurements
Accurate stair calculations are crucial for safety, building code compliance, and user comfort. Understanding the relationship between rise, run, and total dimensions ensures your stairs are both functional and legal.
Safety Considerations
- •Uniform step dimensions prevent tripping
- •Proper handrail height for stability
- •Adequate headroom prevents head injuries
- •Building code compliance for legal requirements
Calculation Formulas
Number of Steps = Total Rise ÷ Rise per Step
Total Run = (Steps - 1) × Run (Standard)
Total Run = Steps × Run (Flush)
Stringer Length = √(Total Run² + Total Rise²)
Comfort Rule: 2 × Rise + Run ≈ 25"
Note: Always check local building codes as requirements may vary by location. Consider hiring a professional for complex installations.
Mount Types Explained
Standard Mount
The last step lands on the floor level. Total run = (number of steps - 1) × run per step. Most common for interior stairs.
Flush Mount
The top of the last step aligns with the floor height. Total run = number of steps × run per step. Often used for deck and outdoor stairs.