Why auditoriums slope upward and what C-value means
Anyone designing a cinema auditorium will sooner or later encounter the concept of rake - the slope of the seating. It is not enough for seats to simply rise toward the projection booth; the critical question is how much each successive row must rise so that the viewer can see the bottom edge of the screen past the heads of the people sitting directly in front. This minimum clearance of the sightline over the head of the next-row viewer is called the C-value.
C-value is the distance by which the line of sight from a seat to the bottom edge of the screen clears the top of the head of the viewer sitting in the immediately preceding row. The higher the C-value, the more comfortable the visual experience. A low C-value means the viewer must actively search for a gap between heads - reducing the enjoyment of the screening.
How our calculator computes the auditorium slope
The sightline curve is not a simple straight line - it is a geometrically derived floor height for each seat, depending on the distance from the screen, screen top height, row spacing and viewer height. The calculator computes this curve iteratively for each row separately and shows where the auditorium meets the required C-value and where it does not.
The result is a graphical and tabular view of how well each row sees. The designer can still adjust parameters before construction begins - row spacing, height of the first row above the reference floor level, screen placement - and verify the impact of changes in real time.
Try our sightline and rake calculator and design the optimal rake for your cinema auditorium.