Stair Calculator

What is a Stair Calculator?

A stair calculator is a practical tool designed to help architects, builders, and homeowners determine the optimal dimensions of stairs, including step rise, step run (tread depth), total run, total rise, and stair angle. It ensures that staircases are safe, comfortable, and compliant with international building standards such as ISO 14122 and other ergonomic guidelines.

Why Stair Dimensions Matter?

Incorrect stair dimensions can make staircases uncomfortable or even dangerous. Key factors include:

• Rise (Riser Height): The vertical height of each step, typically between 150 mm and 200 mm for residential stairs.
• Run (Tread Depth): The horizontal depth of each step, usually between 230 mm and 300 mm. Runs smaller than 230 mm can feel unsafe, while runs above 300 mm may feel awkward.
• Stair Angle: Ideally between 30° and 37°. Angles above 42° are considered unsafe and non-compliant with most standards.
• Formula Check: The well-known ergonomics formula 2 × rise + run ≈ 600–640 mm helps to balance stride length and comfort.

ISO and Building Standards

According to ISO 14122-3 and many national building codes, staircases must provide both safety and comfort. Typical recommendations are:

• Riser height: 150–200 mm
• Tread depth: 230–300 mm
• Angle of inclination: 30°–37° optimal, maximum 42°
• Consistent step dimensions throughout the staircase to avoid tripping hazards

Why Use This Stair Calculator?

• Instant Ergonomics Check: Automatically evaluates whether your stair design is Good, Warning, or Poor.
• Standards-Based: Uses ISO and ergonomic guidelines for accurate results.
• Flexible Units: Supports mm, cm, m, inches, and feet.
• Dynamic Variants: Shows multiple step options (e.g., 10 steps vs. 11 steps) for comparison.
• User-Friendly: Clear results with color-coded ergonomics and tooltips for explanations.

How to Use

1. Enter the Total Rise (vertical height between floors).
2. Optionally, enter the Total Run (horizontal length available) or desired Step Run.
3. Select your preferred units (mm, cm, m, inches, feet).
4. The calculator will display possible stair designs with step rise, run, angle, and ergonomic rating.

Example Calculations

Case 1: A total rise of 280 cm with 15 steps results in ~18.7 cm risers, 25 cm runs, and ~37° angle → Good ergonomics.

Case 2: A total rise of 200 cm with only 10 steps gives risers of 20 cm and a steep 42° angle → Warning, close to unsafe.