The plastic number is a special ratio in architecture with which a whole series of interrelated relationships are associated. These relationships form the basis of a theory of relationships, developed by Dutch architect, thinker and Benedictine monk Dom Hans van der Laan (1904-1991). Following and as an extension of the Golden Number phi (1.618…) related in a certain respect, the plastic number is often indicated with the Greek letter psi (ψ) and has the value 1.3247… The plastic number is based on the spatial relationships between lines, surfaces, and volumes and says something about the ratio of thickness, length and width of parts to each other.

St. Bernadictusberg Abbey – Lemiers

“The plastic number is a design principle, such as the Fibonacci series, the golden ratio and the teachings of Symmetry. The plastic number has its origin in the way we experience space. Dom van der Laan said about this: “You can only see how big something is when you see it in relation to something else. You can only estimate the size of a tree if you see it in a space next to another tree.” Dom Hans van der Laan was always looking for the relationship between inside and outside, between nature and culture, between length and width” –


St. Bernadictusberg Abbey – Lemiers

A building that was built according to these specific proportions, such as St. Benedictusberg Abbey in Lemiers, he called “the architectonic space” and was also a well-known phenomenon in ancient times. In addition to the astronomical characteristics such as the solstices and equinoxes, the divine design combined with the magical play of light made the building attractive for the gathering of people, gatherings in all kinds of areas in which people become one with the space in which they find themselves.

The Plastic Number in Ancient Architecture

Stonehenge (UK) – Abydos Temple Facade (Egypt) – Oseirion (Egypt) – Temple of Hatshepsut (Egypt) – The Colosseum (Italy)

The Colosseum – Rome


The divine relationship between length and width, culture and nature, inside and outside, shadow and sun; the divine relationship between DARK and LIGHT;

© Willem Witteveen


Book: The Architectorial Space – Dom H. van der Laan