The basic dimension in stairway design is step length, i.e. the average distance that someone from central Europe covers in one step when walking in a relaxed manner. This can vary between 60 and 66 cm, so an average value of 63 cm +/-3 cm is generally used in practice.
When climbing a stairway, an individual moves forward and up, which shortens the step length – by twice the height climbed. The going – i.e. the area of the step where the foot can be set down – also has to be subtracted from the step length. This process of converting pure forward motion into combined forward and upward motion is expressed using the step-length rule:
S = 2h + g
In other words, rise multiplied by two, plus going, equals the average step length, whereby the average step length of 63 cm is a constant for all stairway calculations.
The step-length rule can be used to determine the ideal going for a stairway with a specific rise. The step-length rule is modified for this purpose:
g = S – 2h
If we select a rise of e.g. 17 cm, the equation is as follows:
g = 63 cm – 2 x 17 cm
The result is the ideal going (g) of 29 cm for stairways with a rise (h) of 17 cm.
If we approach the design process the other way around, we can also use the step-length rule to calculate the ideal rise for a given going. Again, the step-length rule has to be modified.
h = (S – g) / 2
If we now insert the going of 29 cm into the equation we get the following:
h = (63 cm – 29 cm) / 2
This produces a rise (h) of 17 cm as the ideal rise for stairways with a going (g) of 29 cm.
Experience from accidents has shown that the step-length rule is a very practical guide. When working with goings between 26 and 32 cm, it creates rises that are perfect from a safety standpoint. When working with rises between 14 and 17 cm, it produces extremely safe goings. Stairways with steps that feature a rise of 17 cm, a going of 29 cm and a pitch of around 30º are particularly safe. They are also very easy to climb, since the rise-to-going ratio of 17:29 is also the most economical.
However, it is not always possible to achieve the standard dimensions in industrial environments, where technical circumstances and the available space can play a decisive role. For example, a typical set of machine steps is usually planned with a rise and going of 21 cm each and a pitch of around 45º. Naturally, the higher rise makes these steps steeper and – at 21 cm – the going is also less than ideal. Overall, however, these steps are perfectly suited to their purpose.
In terms of ascending, the step-length rule always produces easy-to-climb stairways. In terms of descending, it can on occasion be desirable to have slightly larger goings.