How do I calculate home theatre screen size from viewing distance?

Choose a horizontal viewing angle, calculate the required image width from the eye-to-screen distance, then convert that width to a diagonal using the screen aspect ratio. This calculator shows 36-degree and 30-degree comparisons.

Why does aspect ratio change the diagonal size?

A 16:9 screen and a 2.35:1 screen with the same image width have different heights and therefore different diagonals. Viewing angle is driven primarily by image width, so compare width as well as diagonal.

Is screen size enough to select a projector?

No. Projector selection also requires throw distance, lens shift, image brightness, screen gain, ambient-light control, resolution, mounting position and ventilation checks.

Free theatre planning tool · Updated 15 August 2026

Screen Size &
Viewing Angle Calculator.

Measure from the viewer’s eyes to the screen plane. This tool converts that distance into two horizontal viewing-angle comparisons and checks the angle created by your proposed screen.

Calculate screen size Plan a Jaipur theatre

Early planning aid only. Final screen and projector selection must also verify sightlines, throw ratio, lens shift, brightness, screen gain, acoustics, speaker placement and room finishes.

Design around image width, not a catalogue diagonal. The same diagonal produces a different image width at 16:9 and 2.35:1. Seating distance, content mix and room geometry should be decided together.

Calculate screen size and angle

36° viewing-angle diagonal 94 in

At 3.2 m with a 16:9 screen.

30° comparison diagonal: 77 in
36° image width: 2.08 m
Current 100 in angle: 38.2°
Current image width: 2.21 m

Screen geometry does not prove that a projector can light the image adequately or fit the available throw distance.

How the calculator works

Image width: 2 × viewing distance × tan(horizontal angle ÷ 2). The width is then converted to diagonal using the selected aspect ratio.

36° target

Uses the horizontal viewing angle published by THX for screen placement from the farthest seat.

30° comparison

Shows how a narrower field of view changes image width and diagonal at the same seat.

Current screen

Converts your entered diagonal to image width and calculates its horizontal angle from the selected seat.

Do not freeze the screen before these checks

Measure eye position for the front and farthest seats, not just wall-to-wall room length. Confirm usable screen-wall width after columns, curtains, speakers and acoustic build-up. Check projector throw range and lens shift at the intended mounting location. Calculate screen luminance from projector output, calibrated light, image area and screen gain. Coordinate centre-channel and left/right speaker placement with screen type and width. Draw unobstructed sightlines for every row before platform and ceiling work. Confirm content mix before choosing 16:9, 2.35:1 or masking strategy. Leave service access, ventilation and replaceable cable pathways at projector and rack.

Primary reference

The calculator uses geometry plus THX’s published 36° screen-placement guidance. Read the source and treat the result as one design input, not a complete theatre specification.

THX — Certified screen placement and 36° horizontal viewing angle

Planning a dedicated room in Jaipur?

We coordinate screen, projector, speakers, acoustics, lighting and control before the fit-out begins.

Home theatre installation Call +91 96944 41610