Riser heights and sightlines — so row 2 doesn't hate the build
Row 2 in a flat-floor theater looks at the back of row 1's heads. For a typical 120-inch screen with rows 52 inches apart and a screen bottom 24 inches off the floor, row 2 needs about 7-10 inches of riser to clear sightlines to the bottom of the picture. Row 3 needs 14-20 inches on top of that.
This calculator computes the riser height for each row using head-clearance geometry, then validates each seat against the SMPTE 30-degree viewing-angle minimum so you don't build a riser that puts row 2 too far back to enjoy the screen.
Use this before framing a platform — riser height drives ceiling clearance, step run, and whether you need a structural engineer.
How the Riser Height Formula Works
The Formula
For each row past the first, the calculator solves for the riser height that puts the seated eye point above the line from the prior row's head to the bottom of the screen. riser_height = (prior_eye_height + head_clearance) - target_eye_height_at_floor, where head_clearance is the 4-inch SMPTE allowance for a clear sightline to the screen bottom. Viewing angle per row uses angle = 2 x atan(screen_width / (2 x distance_to_row)); rows below 30 degrees are flagged.
Worked Example
Screen: 120 inches diagonal (104.6" wide), bottom at 24 inches off the floor. Row 1 distance: 120 inches (10 feet). Row 2 distance: 172 inches (row spacing 52 inches). Eye height in a theater recliner: ~38 inches. The sightline from row 2's eye to the bottom of the screen must clear row 1's head by 4 inches. Row 1 head height ~ 50 inches; clearance target = 54 inches at row 1's position. Riser height for row 2: (50 + 4) - 38 = 16 inches at row 1's x, scaled along the sightline = ~8 inches at row 2's position. Row 3 at 224 inches stacks ~16-18 inches total.
Standards
The 4-inch head-clearance allowance comes from SMPTE EG-18 (Design of Effective Cine Theaters) and matches the CEDIA installer guideline. SMPTE 30-degree minimum viewing angle is from SMPTE ST 196M — narrower than the 36-degree THX preference, but the practical floor below which a screen feels like a monitor. Seat eye heights: theater recliner ~38", standard sofa ~32", barstool ~44-46".
Limitations
Risers over 18 inches stack risk: code-required guardrails, structural-load calc for the platform, and ceiling clearance for the rear row. Above 18 inches the calculator emits a structural warning — that's the cue to involve an engineer, not ignore the math. The model also assumes everyone seated is roughly the same height; mixing kids in the front row and adults in the back row makes the geometry easier, not harder. Sloped floors and curved rows aren't modeled; use a CAD pass for non-rectangular layouts.
