The C-value is the vertical distance (in mm) between the sightline of a viewer and the top of the head of the viewer sitting directly in front. The higher the C-value, the more comfortable the view and the steeper the floor rake. SMPTE EG-18 recommends a minimum of 60 mm; 100 mm is recommended for new builds.

What is the sightline reference point?

The reference point is the bottom edge of the projected image on the screen. The calculator verifies that every viewer can see this edge over the head of the person in front. Visibility of the top edge is generally achieved automatically.

How much does the row pitch matter?

The row pitch directly affects the overall floor rake. A larger pitch (deeper seats) reduces the required rake; a narrower pitch increases it. A typical cinema row pitch is 0.9 to 1.1 m.

What does the viewing angle to the screen mean?

The viewing angle is the angle at which a viewer sees the full width or height of the screen. SMPTE recommends that the rear row sees the image width at a minimum of 26 degrees; the front row should not exceed 45 degrees for comfortable viewing.

Can the results be used directly in a project?

The calculator provides indicative results for the pre-design phase. The final auditorium project must be prepared by a certified designer who takes acoustics, regulatory requirements and site-specific constraints into account.

Auditorium sightline curve

The ideal floor rake, row heights and viewing angles so every seat sees the full screen.

// screen

Screen width (m)

Screen height (m)

Screen bottom above floor (m)

// auditorium

First row distance (m)

Row spacing (m)

Rows

First row floor height (m)

// viewer

Seated eye height (m)

Target C-value (m)

// sightline curve (rake)

GoodMarginalPoor

Scaled section through the auditorium. Thin rays run from each row's eyes to the bottom of the screen, just grazing the head in front (the C clearance). Colour = view quality.

Floor rise

1.73 m

Highest row

1.73 m

C clearance

120 mm

// viewing angles

Front row · Image width

49°

Back row · Image width

26°

Front row · Look-up

27°

Every row sees the full screen with the set clearance.

// row

Row	Distance	Floor	Screen	Look-up
1	12.0	0.00	49°	27°
2	13.1	0.12	46°	25°
3	14.1	0.24	43°	23°
4	15.2	0.38	40°	21°
5	16.2	0.52	38°	19°
6	17.3	0.68	35°	17°
7	18.3	0.84	33°	16°
8	19.4	1.00	32°	15°
9	20.4	1.18	30°	14°
10	21.5	1.35	29°	12°
11	22.5	1.54	27°	11°
12	23.6	1.73	26°	11°

Front row: 12.0 m · Back row: 23.6 m

Indicative calculation using the C-value method and SMPTE EG-18 guidance. Consult a venue designer for the final layout.

The sightline curve (also called the rake) describes how steeply the auditorium floor must rise so that every viewer can see the bottom edge of the screen over the head of the person sitting in the row in front. The calculation is based on the C-value, the vertical clearance between the sightline and the top of the head of the viewer ahead.

A correctly designed sightline curve is the foundation of a comfortable cinema experience. A floor that is too flat causes poor visibility in the rear rows; one that is too steep is physically demanding and increases construction costs. SMPTE EG-18 recommends a C-value in the range of 60 to 120 mm.

The calculator computes the floor height, viewing angles to the bottom and top edge of the screen, and the overall rake for each row. Results can be exported to project documentation or handed to the auditorium architect.

How it works

Enter screen parameters
Fill in the screen width and format and the height of the bottom edge of the image above the reference floor level (usually 0 m). These values define the aiming point of the sightline calculation.
Set the auditorium geometry
Enter the distance from the front row to the screen, the row pitch, the number of rows and the floor height of the first row. These parameters define the seat positions along the sightline axis.
Choose eye height and C-value
The standard seated eye height is about 1.15 m above the row floor. A C-value of 60 mm is the minimum; 100 mm is a comfortable value for new venues.
Review the result
The table shows the floor height and viewing angles for each row. The diagram displays a scaled cross-section of the auditorium. Row colour indicates sightline quality: green = good, orange = marginal, red = poor.

Frequently asked questions

What is the C-value?: The C-value is the vertical distance (in mm) between the sightline of a viewer and the top of the head of the viewer sitting directly in front. The higher the C-value, the more comfortable the view and the steeper the floor rake. SMPTE EG-18 recommends a minimum of 60 mm; 100 mm is recommended for new builds.
What is the sightline reference point?: The reference point is the bottom edge of the projected image on the screen. The calculator verifies that every viewer can see this edge over the head of the person in front. Visibility of the top edge is generally achieved automatically.
How much does the row pitch matter?: The row pitch directly affects the overall floor rake. A larger pitch (deeper seats) reduces the required rake; a narrower pitch increases it. A typical cinema row pitch is 0.9 to 1.1 m.
What does the viewing angle to the screen mean?: The viewing angle is the angle at which a viewer sees the full width or height of the screen. SMPTE recommends that the rear row sees the image width at a minimum of 26 degrees; the front row should not exceed 45 degrees for comfortable viewing.
Can the results be used directly in a project?: The calculator provides indicative results for the pre-design phase. The final auditorium project must be prepared by a certified designer who takes acoustics, regulatory requirements and site-specific constraints into account.

Something not working?