The bidirectional TV size & viewing distance suite. Enter your seating distance and we solve the ideal screen size — or enter your TV size and we solve the ideal seating range. THX, SMPTE, and 4K visual-acuity modes, with honest trigonometry throughout.
✓ 100% client-side — your room measurements never leave this browser.
ⅠPick your room
Start from a typical seating distance, then fine-tune below. These presets cover the most-searched room types.
ⅡThe suite
Four calculators, one engine. Switch units any time — every result converts instantly.
25° relaxed30° SMPTE36° THX50° front row
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your pick
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THX 36° recommended
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SMPTE 30° minimum
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min. size to resolve full 4K
Top-down view: the gold arc is your horizontal viewing angle.
Quick picks: jump straight to a common size and see the numbers.
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ideal distance range
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your viewing angle now
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4K detail visible if closer than
Enter values
nearsweet spot (THX ↔ SMPTE)far
Reading the gauge: the green band is the sweet spot between THX's 36° (closer) and SMPTE's 30° (farther). The gold marker is where you sit now. The blue tick is the 4K acuity limit — sit closer than it to resolve every 4K pixel.
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screen center height (mount here)
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top of screen
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bottom of screen
The rule: screen center = seated eye level. Mounting above a fireplace usually breaks this rule — if you must, tilt the TV down toward the seats so the screen normal points at eye level.
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max diagonal that fits
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largest standard size that fits
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its actual width
Standard sizes that fit your wall:— Assumes a 5% visual margin so the TV doesn't look crammed against the wall edges, plus your bezel allowance.
ⅢQuick reference chart
Ideal seating distances for popular sizes, solved by the same engine. Distances in feet.
TV size
Screen W × H
THX 36° (closer)
SMPTE 30° (farther)
4K fully resolved if closer than
55″
47.9 × 27.0″ (122 × 68 cm)
6.1 ft
7.5 ft
3.6 ft
65″
56.7 × 31.9″ (144 × 81 cm)
7.3 ft
8.8 ft
4.2 ft
75″
65.4 × 36.8″ (166 × 93 cm)
8.4 ft
10.2 ft
4.9 ft
85″
74.1 × 41.7″ (188 × 106 cm)
9.5 ft
11.5 ft
5.5 ft
ⅣHow the math works
No black boxes. Every number on this page comes from these formulas.
THX 36° is THX's recommended viewing angle for the back row of a theater. SMPTE 30° is SMPTE's minimum viewing angle for HDTV. Both are horizontal angles.
4K visual acuity (honest derivation). 20/20 vision resolves about 1 arcminute. A 4K panel has 2160 vertical pixels, so one pixel spans (screen height ÷ 2160). The distance at which that pixel subtends exactly 1 arcminute is (height/2160) / tan(1′) ≈ 1.5915 × screen height — equivalent to about a 58.4° viewing angle. Sit closer than this and your eyes can genuinely resolve every 4K pixel; sit farther and 4K is visually identical to 1080p. That's why 4K lets you sit much closer than the old 1080p rules allowed.
Mounting height. Screen center = seated eye height (average 42″ / 107 cm). Top and bottom follow from screen height.
Sanity check. Independent size guides (such as rtings.com's TV size guide) converge on the same conclusion this math gives: for 4K, err larger — a 65-inch TV at 8–9 feet sits right in the 30–36° window where both SMPTE and THX agree.
Wall fit. Usable width = wall × 95% − 2 × bezel, then max diagonal = usable ÷ 0.8716.
ⅤTV size questions, answered
The most-searched questions about TV size and viewing distance.
What size TV should I get?
Measure how far you sit from the screen, then pick a target viewing angle. THX recommends a 36-degree horizontal viewing angle for a cinematic feel (a 10 ft viewing distance calls for roughly an 89-inch TV), while SMPTE's 30-degree minimum gives about 74 inches at the same distance. Use the calculator above: enter your seating distance and it solves the exact size for THX, SMPTE, and 4K modes.
What size TV should I get for a bedroom?
Bedroom viewing distances are typically 6 to 9 feet. At 8 feet, THX's 36-degree recommendation works out to about a 71-inch TV and SMPTE's 30-degree minimum to about a 59-inch TV, so a 65-inch set is the sweet spot for most bedrooms. If you watch from bed at an angle, lean toward the larger end of the range.
What size TV should I get for a dorm room or small living room?
In a dorm or small living room you usually sit 5 to 7 feet from the screen. At 6 feet, SMPTE's 30-degree guideline suggests about 44 inches and THX's 36-degree guideline about 54 inches, so a 50 to 55-inch TV is ideal. Going much bigger at that distance pushes you past 40 degrees of viewing angle, which feels overwhelming for casual viewing.
What size TV should I get for a 12x12 room?
In a 12x12 ft room the sofa is usually about 8 to 9 feet from the TV wall. At 9 feet, THX suggests roughly 80 inches and SMPTE about 66 inches, making 65 to 75 inches the practical range. A 75-inch TV at 9 feet gives you a 34-degree viewing angle, right inside the cinematic sweet spot.
How far should I sit from a 55, 65, or 75 inch TV?
For a 55-inch TV, the ideal range is about 6.1 ft (THX 36 degrees) to 7.5 ft (SMPTE 30 degrees). For 65 inches it's about 7.3 to 8.8 ft, and for 75 inches about 8.4 to 10.2 ft. Sit closer than the THX number and the picture fills your vision like a theater; sit farther than the SMPTE number and you're leaving immersion on the table.
Can a TV be too big for a room?
Yes. Past about 50 degrees of viewing angle most people have to turn their heads to follow the action, which gets tiring fast, and you can start seeing individual pixels on 1080p screens. The wall-fit check in this tool also flags the physical limit: a good rule is that the TV's total width shouldn't exceed about 95% of the wall it's on. When in doubt, measure your wall first.
What is the difference between THX and SMPTE viewing distance?
THX recommends a 36-degree horizontal viewing angle for the back row of a theater, which means sitting closer or buying bigger: size equals roughly 0.75 times your viewing distance. SMPTE's minimum is 30 degrees, which works out to size equals roughly 0.61 times viewing distance. THX is the more cinematic of the two; SMPTE is the comfort-first baseline used in broadcast standards.
What is the best viewing distance for a 4K TV?
Because 4K packs four times the pixels of 1080p, you can sit much closer before pixels become visible. A common rule is 1 to 1.5 times the screen height for full 4K benefit. This tool's 4K acuity mode goes further: it computes the exact maximum distance at which a person with 20/20 vision can still resolve individual 4K pixels, so you know precisely where the extra detail stops mattering.
How is the 4K visual-acuity distance calculated here?
We use the standard limit of human vision: 20/20 eyesight resolves about 1 arcminute. A 4K screen has 2160 vertical pixels, so the pixel pitch is screen height divided by 2160. The distance where that pitch subtends 1 arcminute is (screen height / 2160) / tan(1 arcminute), about 1.59 times the screen height. Sit closer than that and you can genuinely see every 4K pixel; sit farther and a 4K panel looks identical to 1080p to your eyes.
What size TV is best for gaming?
For console and PC gaming, most players prefer the THX end of the range or slightly beyond it, around 36 to 40 degrees, because games reward peripheral immersion. At 6 feet that means 55 to 65 inches; at 8 feet, 65 to 75 inches. Also check input lag and 120Hz support on the specific model, since size math can't tell you how responsive a panel is.
How high should a TV be mounted on the wall?
The center of the screen should sit at your seated eye level, which averages about 42 inches (107 cm) off the floor. So for a 65-inch TV (about 32 inches tall), the center goes at 42 inches, the top lands near 58 inches, and the bottom near 26 inches. Mounting higher, like above a fireplace, forces your neck to tilt up; if you must, tilt the TV down toward the seating position.
How do I know what size TV fits on my wall?
Measure the wall's width, subtract about an inch per side for the bezel, and leave a 5% visual margin so the TV doesn't look crammed in. Divide the remaining width by 0.8716 (the width-to-diagonal ratio of a 16:9 screen) to get the maximum diagonal. For example, a 100-inch-wide wall fits up to about a 107-inch diagonal, so a 98-inch TV is the largest standard size that works.
Does TV size math differ between Samsung, LG, and Sony?
No. Viewing distance, viewing angle, and screen dimensions are pure geometry of the 16:9 panel and work identically for every brand. Where brands differ is panel technology (OLED vs QLED vs Mini-LED), brightness, and processing, which affect picture quality but not the size math. A 65-inch Samsung and a 65-inch LG have the same screen width and height.
How do I calculate TV size in centimeters?
Use the unit toggle in the calculator to work in metric throughout. The geometry is identical: a 65-inch (165 cm) 16:9 TV is 144 cm wide and 81 cm tall. For a quick mental conversion, one inch of diagonal equals 2.54 cm, so a 55-inch TV is a 140 cm TV.
Should I get a 55 or 65 inch TV if I sit 8 feet away?
At 8 feet, a 65-inch TV gives you a 31-degree viewing angle, just inside SMPTE's 30-degree minimum, while a 55-inch TV gives about 26 degrees, which feels small and distant. Unless the room is very bright or you strongly prefer a subtle picture, 65 inches is the better pick at 8 feet. Most buyers regret going too small far more often than going too big.
Do I measure viewing distance from the screen or the wall?
Measure from your eyes to the surface of the screen, not from the sofa to the wall. A TV mounted on the wall sits a few inches in front of it, and a TV on a stand can be a foot or more into the room. That difference matters at short distances: at 6 feet, 6 inches of error changes your viewing angle by almost 2 degrees.
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