Stair Calculator
Stair Calculation Guide
Our professional stair calculator helps architects, builders, and DIY enthusiasts design comfortable and code-compliant staircases. Proper stair design is essential for safety, comfort, and building code compliance in residential and commercial projects worldwide.
How the Stair Calculator Works
The calculator uses industry-standard formulas to determine optimal stair dimensions based on your input parameters. You can choose between two calculation methods:
1. Standard Calculation
Enter your total rise (floor-to-floor height) and desired riser height. The calculator will:
- Calculate the number of steps needed
- Adjust riser height for even distribution
- Determine comfortable tread depth using the “rule of 25” formula
- Calculate total run and incline angle
- Generate a visual diagram of your staircase
2. Custom Calculation
For existing designs or specific requirements, enter your exact tread depth, riser height, and number of steps to:
- Verify compliance with safety standards
- Calculate total run and angle
- Check comfort using the step proportion formula
- Visualize your custom stair design
Key Benefits of Our Calculator
Interactive Diagram
Visual representation of your staircase with all key dimensions clearly labeled.
Dual Calculation Modes
Standard mode for new designs and custom mode for existing stair analysis.
Code Compliance
Helps design stairs that meet international building code requirements.
Understanding Stair Calculations
Professional stair design follows these fundamental principles:
Blondel’s Formula (Rule of 25)
The optimal stair proportion follows: 2×Riser + Tread = 600-650mm
This formula, developed by French architect François Blondel, creates comfortable stair proportions that match natural human stride.
Building Code Requirements
Most international building codes require:
- Maximum riser height: 200mm
- Minimum tread depth: 225mm
- Consistent riser/tread dimensions (variation ≤5mm)
- Minimum width: 800mm for residential, 1000mm for public stairs
Frequently Asked Questions
The diagram is a scaled representation of your calculated dimensions. It accurately shows the proportions and relationships between risers and treads, with all measurements matching your calculated values. The diagram automatically adjusts to display any stair configuration within standard building parameters.
The most comfortable stairs follow Blondel’s formula where twice the riser height plus the tread depth equals approximately 600-650mm. For example, with a 175mm riser, the ideal tread would be 600 – (2×175) = 250mm. Our calculator automatically optimizes this relationship.
Yes, the calculator works for both residential and commercial stairs. For public buildings, you may need to use more conservative dimensions (typically lower risers and deeper treads) to accommodate a wider range of users. Always check local building codes for specific requirements.
The calculator slightly adjusts riser heights to ensure all steps are exactly equal while maintaining code compliance. Uneven risers are a major safety hazard. The adjustment is typically minimal (a few millimeters) and distributes the difference evenly across all steps.
The angle indicates how steep your staircase will be: 30-35° is ideal for comfort, 37° is standard for residential stairs, and angles above 40° become uncomfortably steep. The diagram visually represents this angle so you can see the steepness before construction.