The ideal riser height is between 17-18 cm (6.7-7.1 inches). This provides a comfortable step height for most people while maintaining safety. Building codes typically require risers to be between 15-20 cm.

To calculate the number of steps:
1. Measure the total vertical height (from floor to floor)
2. Divide by your desired riser height
3. Round to the nearest whole number
4. Recalculate the actual riser height by dividing total height by number of steps

The 18-inch rule states that the sum of the tread depth (in inches) plus twice the riser height (in inches) should equal approximately 18 inches (46 cm). This formula (2R + T = 46 cm) helps create comfortable stairs that follow ergonomic principles.

Most building codes require a minimum tread depth of 25 cm (10 inches) for residential stairs. For commercial or public buildings, this is often increased to 28 cm (11 inches). Deeper treads provide more comfortable and safer stairs.