How we calculate

Screen width, height and area

A TV's advertised size is the diagonal of the screen, corner to corner — not its width and not counting the bezel. For a 16:9 screen, the width and height are fixed fractions of that diagonal:

• width = diagonal × 0.8716 (the factor is 16 ÷ √337)
• height = diagonal × 0.4903 (the factor is 9 ÷ √337)
• area = width × height

So a 65″ TV is about 56.7″ wide and 31.9″ tall. For any other aspect ratio we use the same idea — height = diagonal ÷ √(r² + 1) and width = r × height, where r is the width-to-height ratio. These two factors underpin nearly everything else on the site, because viewing angle and mount height both depend on the screen's real width and height, not its diagonal.

Viewing distance and viewing angle

The right seating distance is the one where the screen fills a comfortable slice of your horizontal field of view — its viewing angle. Given a target angle θ, the distance that makes a screen fill exactly that angle is straightforward trigonometry:

distance = (½ × screen width) ÷ tan(θ ÷ 2)

We use the recognized angle standards: THX's 40° for an immersive, cinema-like fill; about 36° as the balanced sweet spot; and SMPTE's 30° as a relaxed minimum. Worked the other way — to recommend a size for a known distance — we invert the same equation: diagonal = 2 × distance × tan(θ ÷ 2) ÷ 0.8716. In everyday terms these standards land on simple multipliers of the diagonal: roughly 1.2× the diagonal for immersive, about 1.4× for balanced, and around 1.6× for relaxed. That's where the popular "seating distance ÷ 1.4 ≈ ideal 4K size" rule of thumb comes from.

Is 4K or 8K worth it? — pixel acuity

Whether a resolution is "worth it" is a perception question, not a marketing one. A person with 20/20 vision can resolve detail down to about one arc-minute — one-sixtieth of a degree (the Snellen acuity basis). For a screen with a given number of pixel rows, there's a distance past which each pixel subtends less than that, so the pixels blur together and a higher resolution stops looking any sharper:

acuity distance = screen height ÷ (vertical pixels × tan(1 arc-minute))

Closer than that distance, you can resolve the resolution's pixels; farther away, you can't. So 4K is worth it when you sit closer than the acuity distance for 1080p, and 8K is worth it only when you sit closer than the acuity distance for 4K. As multipliers of the diagonal, those cutoffs are about 1.6× for 4K and 0.8× for 8K — which is why, on a 65″ at normal living-room distances, 4K pays off and 8K almost never does.

Mounting height and tilt

A TV is most comfortable when the center of the screen meets your eye line where you sit. For a flat mount that simply means the center sits at your seated eye level — about 42 inches from the floor for a typical sofa (the SANUS/SMPTE convention). When the TV has to sit higher, a downward tilt re-aims it at your eyes, and the center rises by the tilt over the distance:

• screen center = eye level + (distance × tan(tilt))
• bottom of screen = center − (screen height ÷ 2)

where screen height ≈ diagonal × 0.49 from the geometry above. If a mantel or dresser forces the TV to a higher center, we recommend the tilt that re-aims it: tilt = arctan((center − eye level) ÷ distance). We start eye height from your viewing position — seated 42″, reclined 34″, lying in bed 28″, standing 58″ — all of which you can fine-tune, consistent with CEDIA's display and mounting ergonomics.

Energy use and running cost

Running cost is just power over time at your electricity rate. From the TV's wattage, your hours per day, and your rate, the annual figures fall out directly — and we include standby draw for the hours the TV is off:

annual kWh = (watts × hours ÷ 1000 + standby watts × (24 − hours) ÷ 1000) × 365

Multiply annual kWh by your rate for the yearly cost (and by ten for a ten-year estimate); multiply by a grid carbon factor for the CO₂. When you don't know your TV's exact wattage we estimate it from the screen size and panel type, interpolating between known reference figures. Defaults use the US average rate (~$0.16/kWh), 5 hours a day, and a typical standby draw — all editable.