Start on the horizontal centreline, then choose distance by viewing angle and vertical comfort rather than a row letter.
The two reference rooms use one physical scale. The highlighted depth is computed from the published viewing-angle records and clipped to each room's front and back rows.
In a tall purpose-built room, begin in the rear half and move back if the top edge strains your neck. In a shorter room, move forward only until scanning the frame becomes tiring.
Why the two room types feel different
The profiles use one scale. Verified screen facts are mixed with clearly marked design assumptions where full architectural surveys were not published.
The purpose-built profile is not an as-built survey of BFI IMAX. The retrofit profile uses published Greenwich dimensions and distances, but some seating geometry is estimated. Both are visual references, and both carry estimated confidence.
What the published guidance says
verified
SMPTE Engineering Guideline EG 18-1994: 30°
The image should occupy approximately 30 degrees horizontally and at least 15 degrees vertically for the most distant viewer. Nearer viewers up to 80 degrees horizontal were contemplated. The nearest viewer's angle to the top of the image should not exceed 35 degrees.
Applies to: General cinema design, as a historical baseline rather than a current requirement.
SMPTE withdrew this guideline in 2003 and explicitly says its criteria may be obsolete and are no longer endorsed. The 30-degree value is a farthest-seat minimum, not a claim that 30 degrees is the one best seat.
verified
THX Certified Screen Placement: 36°
Design for a 36-degree horizontal viewing angle from the farthest seat, with unobstructed sightlines from every seat.
Applies to: THX cinema design and screen placement.
THX presents 36 degrees as the angle from the farthest seat. It is wider than the old SMPTE 30-degree baseline.
reported
Original IMAX theatre design criterion, documented by the Giant Screen Cinema Association: 53°
Keep the back row within one screen width of the screen plane. GSCA says the original IMAX design corresponding to this rule called for a minimum viewing angle of at least 53 degrees.
Applies to: Purpose-built flat giant-screen cinemas and the original IMAX geometry, not ordinary multiplex retrofits.
This is GSCA's account of IMAX's original design rule, not a current numerical recommendation published on IMAX.com. GSCA also reports that most giant-screen front rows are no closer than 0.3 screen widths.
verified
Will Szabo, SMPTE Journal, 1976: 60°
A large-screen cinema approaches immersion when the image occupies 60 degrees horizontally and 30 degrees vertically. Oblique viewing angles to significant action should not exceed 45 degrees.
Applies to: Purpose-designed large-screen motion-picture theatres.
This is a large-screen immersion target, not a comfort maximum. It is roughly twice the old SMPTE general-cinema farthest-seat angle.
These values describe different goals. The oldest SMPTE guideline is withdrawn and remains only as a labelled historical reference.
A practical method
Centre
Choose the horizontal centreline to reduce side-angle distortion.
Look up
In a full-height room, move back if the top edge requires a sustained head tilt.
Move forward
In a shorter room, stop when repeated eye or head movement becomes tiring.
Check the movie
Full-height sequences make vertical comfort more important than a scope-only presentation.
Professional audio alignment and an IMAX executive's personal recommendation both support a centred seat well behind the midpoint as a starting place, not a universal rule.
Limit: exact best seating depends on screen position, curvature, rake, sightlines, speaker layout, seat map, and your own comfort. If a venue publishes none of that geometry, any precise row recommendation is a guess.