TV Size Calculator

The TV size vs. viewing distance calculation tells you the optimal screen size for your room, or the optimal seating distance for a TV you already own. Sitting too close causes eye strain; too far loses picture detail.

There is no single right answer, and that is the honest starting point

Two organisations publish a number here and they do not agree. SMPTE calls for a 30° horizontal viewing angle, which is the conservative, cinema-reference figure. THX calls for 36° to 40°, which is noticeably more immersive. Both are defensible, they are roughly 35% apart in screen size, and most of the contradictory advice online is really just people quoting one standard at people quoting the other.

This calculator gives you the whole range and lets you pick where in it you want to sit.

The geometry: A 16:9 screen of diagonal d is 0.872 × d wide. To fill a horizontal angle θ from distance D:

Screen width = 2 × D × tan(θ ÷ 2) Diagonal = Screen width ÷ 0.872

Which works out to:

• SMPTE 30° (conservative): diagonal = D ÷ 1.63
• THX 36°: diagonal = D ÷ 1.34
• THX 40° (immersive maximum): diagonal = D ÷ 1.20

TV height and width from the diagonal:

• Width = Diagonal × cos(arctan(9/16)) ≈ Diagonal × 0.872 (for 16:9)
• Height = Diagonal × sin(arctan(9/16)) ≈ Diagonal × 0.490 (for 16:9)

Where resolution comes in

Resolution does not set the ideal size. It sets how close you can get before the pixel grid itself becomes visible, which is a separate limit:

• 1080p (Full HD): structure shows up closer than about 1.5× the diagonal. On a 1080p set this limit bites first, so it, not the viewing angle, is what caps your size.
• 4K (Ultra HD): resolves cleanly to about 1.0× the diagonal. That is closer than 40° immersive seating, so your field of view runs out before the pixels do.
• 8K: the pixels stop being the constraint entirely. In a normal living room 8K buys you nothing you can see, which is why the size answer for 8K is the same as for 4K.

Quick reference table (4K):

Those upper figures look enormous written down. They are also what the standard says. My own bias, for what it is worth, is toward the larger end of the range: regret about buying a TV too big is a lot rarer than regret about buying one too small, and the wall it has to fit on is usually the real constraint anyway.

Worked example: Sofa is 9 feet (108 inches) from the TV wall, 4K. Conservative: 108 ÷ 1.63 = 66 inches. Immersive: 108 ÷ 1.20 = 90 inches. So anything from a 65 to an 85 is defensible at that distance. The midpoint lands at 78 inches, and the nearest size anyone actually sells is a 77, which fills 34.5°.

Height consideration: Mount the TV so the center of the screen is at eye level when seated, which is typically 42–48 inches from the floor to screen center.