Formula and units
c = 1000 × [E + (B − E) × p / D − F] mm
E is the viewer’s eye height, F the preceding row’s eye height, and B the picture’s bottom height, all in metres above the same reference floor and including any risers. D is the horizontal distance from the viewer to the picture; p is the horizontal distance forward to the preceding row (0 < p < D), both in metres. Multiplying by 1000 converts the clearance to millimetres.
Worked example
Take E = F = 1.2 m, B = 2.4 m, D = 8 m and p = 1.2 m. The line at the preceding eye is 1.2 + (2.4 − 1.2) × 1.2 / 8 = 1.38 m high. The clearance is (1.38 − 1.2) × 1000 = 180 mm. This falls in UNIC’s acceptable band, 150 mm to below 200 mm.
Assumptions and limits
- UNIC’s How to design a cinema auditorium, second edition, §4.7 uses a seated eye height of 1200 mm. Its bands are good at 200 mm or more, acceptable at 150–<200 mm, poor at 120–<150 mm and unacceptable below 120 mm. These are that guide’s design judgments, not a legal occupant limit or an ADA rule.
- Use the picture format with the lowest bottom edge. The first row has no preceding row, so c is not applicable there. This section calculation does not credit gaps between heads or establish visibility of the whole picture.
- The article separately samples the picture’s bottom edge with assumed head boxes. Head depth, eye-height variation, standing spectators and wheelchair sightlines need their own checks. Raising the picture can improve clearance while increasing the upward viewing angle.