Pythagoras, but for TV
Screen "size" is the diagonal. Given the diagonal d and aspect ratio w:h, the width is d × w/√(w²+h²) and height d × h/√(w²+h²). A 55" 16:9 TV is therefore ≈ 47.9" × 26.9" — and you need a bit more for the bezel.
Viewing distance
- 4K: distance ≈ 1.5 × diagonal (e.g. 55" → ~6.9 ft / 2.1 m) — close enough that pixels vanish
- 1080p: distance ≈ 2.5–3 × diagonal (55" → ~11–14 ft) — sit closer and you see pixels
- Monitor (desk): ~20–30" away — aim for ~24–27" 1440p or 27–32" 4K
Rule of thumb from THX: the screen should fill about 40° of your field of view for immersion — for a 55" TV that's ~5.5 ft.
Frequently Asked Questions
Q: What are the exact dimensions of a 65, 75, or 85 inch TV?
For standard 16:9 widescreen displays: a 65-inch TV is ~56.7" wide × 31.9" high (144 × 81 cm); a 75-inch TV is ~65.4" wide × 36.8" high (166 × 93.5 cm); an 85-inch TV is ~74.1" wide × 41.7" high (188 × 106 cm).
Q: How much wall space does a 100-inch projector screen need?
A 100-inch 16:9 projection screen has an active display width of 87.2 inches (221.5 cm) and a height of 49.0 inches (124.5 cm). Adding standard border bezels requires at least 92" × 54" of unobstructed wall area.
Q: What is the optimal viewing distance for a 4K TV?
For 4K Ultra HD televisions, the recommended viewing distance is 1.2 to 1.5 times the screen diagonal. For a 65" TV, sit about 6.5–8.1 feet (2.0–2.5 m) away; for a 75" TV, sit 7.5–9.4 feet (2.3–2.9 m) away.