Building a screen comparison tool around viewing distance

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.