Inner and outer dimensions
Short definitionThe room measured from panel face to panel face (inner) or from outside of panel to outside of panel (outer). Panels are ordered on outer dimensions. Usable space is discussed in inner dimensions.
The difference between the two is the panel thickness. In a room with 150 mm panels, the outer dimension is 30 cm larger than the inner one in each direction. When a customer says “a 4 × 6 room”, you need to ask which one they mean.
With adjacent rooms it gets less simple: because the shared wall is a single panel, the overall outer dimension is not the sum of the rooms’ outer dimensions. That is why most contractors work in inner dimensions for combined rooms.