Building a screen comparison tool around viewing distance

Alex — Mon, 12 Oct 2026 11:29:51 +0000

A 65-inch TV and a 75-inch TV are easy to compare on a spec sheet. Comparing a desk monitor with a living-room TV or a cinema screen is a different question: how much of your view does each one fill from where you sit?

I built DisplayMath to make that comparison visible, with a free browser calculator and an AR preview for supported iPhones.

Start with the geometry

For a flat screen, the diagonal and aspect ratio give its physical width and height. For a 16:9 screen, width is diagonal × 16 / √337. Resolution affects pixel density, but it does not change those physical dimensions.

Once you know the width, the horizontal viewing angle is a small calculation:

function horizontalFov(width, distance) {
  // Width and distance must use the same unit.
  return 2 * Math.atan(width / (2 * distance)) * 180 / Math.PI;
}

A 65-inch 16:9 screen is about 1.44 m wide. At 2.5 m, it spans roughly 32° horizontally; a 75-inch screen at the same distance spans roughly 37°. Move the seat and both angles change, while the screens stay the same physical size.

Keep two comparisons separate

DisplayMath has a physical-size view for checking dimensions and a From your seat view that accounts for each display’s distance. Separate distance controls let you compare a nearby monitor with a TV farther away.

One detail matters here: equal viewing angles do not guarantee an identical sense of scale or immersion. Room cues, screen distance and picture quality still matter. The calculator shows geometry without turning it into a universal comfort score.

Bring it into the room

On a supported iPhone, you can preview a selected screen panel at actual size on your wall without installing an app. That helps answer the practical question after the math: does this size fit the space? The preview shows the panel, so the bezel, stand and mounting hardware need a separate check.

Try 65-inch vs 75-inch at 2.5 m. The calculators and AR previews are free and need no account.

I’d welcome feedback on whether the distance controls make the comparison easy to understand.

DEV Community: Alex

Building a screen comparison tool around viewing distance

Start with the geometry

Keep two comparisons separate

Bring it into the room