What this calculator does
Viewing distance is set by how much of your field of view the screen should fill. The SMPTE cinema reference is a 30 degree horizontal angle, THX recommends 36 degrees for 4K and 40 degrees for a more immersive setup. A 65 inch 16:9 screen at 40 degrees wants a distance of about 1.98 m.
The standards disagree by a lot, and the difference is a matter of preference rather than of one being correct. The same 65 inch screen wants 2.69 m at the SMPTE angle and 1.98 m at the THX immersive one, a gap of 70 cm. Both are defensible; closer is more cinematic and further is more comfortable for long viewing.
The formula
The screen width is derived from the diagonal and aspect ratio using Pythagoras: width equals diagonal times the ratio divided by the square root of the ratio squared plus one. The viewing distance is then half that width divided by the tangent of half the viewing angle, which is the distance at which the screen subtends the chosen angle.
| Term | Meaning |
|---|---|
| Viewing angle | How much of your horizontal field of view the screen fills. Larger means closer and more immersive. |
| SMPTE 30° | The cinema reference standard, giving a comfortable distance for long viewing. |
| THX 40° | A more immersive recommendation, which places you considerably closer. |
| Screen width | The horizontal dimension, which is what the angle is measured against rather than the diagonal. |
The inputs explained
| Field | What to enter |
|---|---|
| Screen diagonal (in) | Screen diagonal in inches. |
| Aspect ratio | Aspect ratio. Most televisions and monitors are 16:9; ultrawide monitors and cinema formats are wider. |
| Target viewing angle | Target viewing angle, which is the preference decision. |
When to use it
Arranging a room around a television
Working out where the seating should go relative to the screen, or what screen size suits an existing room layout.
Choosing a screen size
Running the calculation backwards from the seating distance you actually have is usually the more practical direction.
Setting up a monitor
The same geometry applies to a desk monitor, though desk depth usually constrains the distance more than preference does.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How far back should each screen size sit?
A range of screen diagonals at the THX immersive viewing angle.
| Screen diagonal | Recommended viewing distance | In metres | Screen width |
|---|---|---|---|
| 43 in | 51.5 in (4.29 ft) | 1.31 m | 37.5 in |
| 55 in | 65.9 in (5.49 ft) | 1.67 m | 47.9 in |
| 65 in | 77.8 in (6.49 ft) | 1.98 m | 56.7 in |
| 75 in | 89.8 in (7.48 ft) | 2.28 m | 65.4 in |
| 85 in | 101.8 in (8.48 ft) | 2.59 m | 74.1 in |
Questions
How far should I sit from a 65 inch TV?
Between about 1.98 m and 2.69 m depending on which standard you follow: 1.98 for the THX immersive 40 degree angle and 2.69 for the SMPTE 30 degree cinema reference. Both are defensible, and personal preference legitimately varies within that range.
Why do the standards disagree?
Because they were written for different purposes. SMPTE describes a comfortable cinema reference where the whole screen sits easily within the field of view. THX targets immersion, which means filling more of it. Neither is wrong; they optimise for different things.
Does resolution change the right distance?
It changes how close you can sit before pixels become visible, which is a different question from how close you should sit. A 4K screen can be viewed closer than a 1080p one of the same size without visible pixel structure, which is why THX revised its recommendation for 4K.
Should I use the diagonal or the width?
The width, which is what the calculation uses internally. The diagonal is how screens are sold but it depends on the aspect ratio, so an ultrawide monitor and a 16:9 television of the same diagonal need quite different distances.
For a screen physical dimensions from its diagonal, see the aspect ratio and screen size calculator. For mounting height, see the TV mounting height calculator.