Theater Calculators

Screens & projection

Screen Viewing Distance Calculator

THX wants about a 40° field of view; SMPTE HD sits nearer 30°. Plug the diagonal and aspect ratio to get width and the two seating distances. Then sit where the picture and the neighbours allow.

Inputs

Units
in

Industry diagonals stay in inches.

16 for 16:9, 2.39 for Scope.

Results

Image width
2.66m
Image height
1.49m
THX 40° distance
3.65m
SMPTE 30° distance
4.96m
UHD 40° distance
3.65m

Recommended gear

Calculation method

Image width comes from the diagonal and aspect ratio. Seating distance is width / (2 tan(θ/2)) with θ = 40° (THX) or 30° (SMPTE).

Exact formula

W = D · a / √(a²+b²) with D in metres. d_THX = W / (2 tan(20°)), d_SMPTE = W / (2 tan(15°)). UHD 40° is the same geometry as THX. Limits: geometric FOV only; no pixel density, no headrest rake, no riser.

THX 40° is not a building code

THX home seating is a 40° horizontal field of view to image width. SMPTE HD sits nearer 30°. Living rooms often land in between because the sofa is against the back wall. The three distances here are geometry from the same diagonal — pick the one that fits the room, then confirm with a tape.

UHD 40° is the same seat as THX

The UHD 40° output uses the same 40° triangle as THX. It is not a pixel-density seat. If you care whether 4K structure is visible, use the retina-distance calculator. Sitting at THX on a 1080p 120-inch sheet can still look soft.

Frequently asked questions

Is THX always 40 degrees?

THX home seating is specified around a 40° field of view to the screen width. It is a starting geometry, not a building code.

Why keep inches on the diagonal?

Retail screens are sold in inches worldwide. Width and seating distance still convert with the metric/imperial toggle.

Does this include 21:9?

Set aspect width/height to 2.39 and 1. The THX/SMPTE angles still apply to the visible width.

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