Updated 19 February 2017 by Thomas
Over the last few years, TVs have been steadily increasing in size. In 2004 the average size of a TV was just 27 inches. This seems tiny compared to today when many people buy TVs with display diagonals of 55 inches and above.
Not only the sizes of TVs have changed, the picture quality has also improved significantly. The old 480p screen resolution was superseded by 720p and now 1080p Full HD has become the new standard. TVs with 4k and even 8K resolution are also now available. As prices for these Ultra High Definition TVs keep dropping more and more people will be tempted to consider them.
There is a never ending flood of new TV models, sizes and resolution becoming available. When you compare TVs it is important to understand the factors that schold be considered when choosing the right size.
Available Space & Budget
When it comes to deciding on screen size, bigger is almost always better. Wile most people will buy a TV based on their budget, the most frequently heard complaint from people who recently bought a TV is that they wish they had saved up and bought a bigger one. Large TVs seem the ver very easy to get used to and even a screen that seemed huge last first will not appear so after some time.
There is a correlation between screen size and seating distance. Your TV will appear smaller the farther away you sit and the screen will fill less of your field of view.
Before looking at more technical ways of calculating the ideal screen size for a TV it is worth bearing in mind that some people are limited by space or do not wish to have a TV which dominates their living room. Particularly when selecting a secondary TV for the kitchen or bedroom, a smaller size is usually preferable.
Below we are looking at two different recommendations from THX and SMTPF to work out the ideal screen size.
THX Screen Size Recommendations
THX recommends a very large screen size in order to provide an immersive cinematic experience. It assumes a viewing angle of 40 degrees. The viewing distance for a given screen size can be easily calculated by dividing the screen diagonal by 0.84. This means the correct viewing distance for a 65-inch TV would be 77 inches or 6.5 feet.
Most people sit about 9 feet away from their TV, which means the correct screen size would be a huge 90 inches. THX do, however, realise that this is beyond the budget of most people and living room space is limited. They therefore recommend a TV of around 60 inches when sitting 6-9 feet away.
Society of Motion Picture and Television Engineers (SMPTE) Recommendation
SMPTE recommends a minimum viewing angle of 30 degrees. This is quite a bit less than THX and most people would find this a comfortable compromise between viewing experience and TV size.
To work out the approximate seating distance simply divide the screen size by 0.6. For a 65 inch TV the seating distance to achieve a 30 degree viewing angle is 108 inches or 9 feet.
Selecting the Right Screen Resolution
If you choose a larger TV or sit closer to the screen, the image quality will reduce as individual pixels become more visible. When moving closer to the screen, the viewing angle will increase and the same amount of pixels will now cover a wider angle. The number of pixels per degree is called the angular resolution. Moving farther away will increase the number of pixels per degree and the image appears sharper.
The limit to increasing image quality in this way is depending on how many pixels per degree the human eye can distinguish. Visual acuity refers to the clarity of vision. A person with 20/20 vision will be able to distinguish 60 pixels per degree. It is worth bearing in mind that this is an average value and it might be possible to distinguish individual pixels from farther away if the contrast between pixels is particularly high.
Full HD Resolution
For a 1080p Full HD TV with a horizontal resolution of 1920 pixels this means the ideal viewing angle to achieve 60 pixels per degree is 32 degrees. This is very similar to the 30 degree viewing angle recommended by SMPTE and a good starting point when selecting a TV.
For a screen size of 55 inches, the viewer would have to be 7 feet away in order to make the most of Full HD resolution. Moving closer would mean the number of pixels per angle would reduce and a higher resolution TV such as a 4K Ultra HD TV would be better. Moving further than 7 feet away would not improve the image quality as the human eye could not see the increased number of pixels per degree. Once the viewer has moved 10.6 feet away, even a TV with 720p resolution would now achieve the ideal resolution of 60 pixels per degree.
4K and 8K Ultra HD TVs
The chart also shows that in order to make the most of a Ultra High Definition TV, it would be necessary to sit unusually close to a TV – much closer than even the immersive 40 degree viewing angle recommended by THX as the ideal viewing angle would be 64 degrees.
This means, the viewer would he to sit just 5.2 feet away from a 4K Ultra HD TV in order to see it at the ideal resolution of 60 pixels per degree.
This would be too close for most people and it might well be worth using the budget which a 4K TV requires to buy a larger Full HD TV instead.
Selecting a 1080 Full HD TV and a screen size and distance based on a 32 degree viewing angle works for most people. For an average viewing distance of 9 feet this means a 70 inch TV would provide the best viewing experience. If planning to sit closer at 7 feet, a 55-inch TV would be the best choice.
4K and even 8K Ultra HD TVs only really make sense if the TV you are planning to buy is very large (65″ and above) or you are sitting exceptionally close to the TV. Keep in mind that 4K content is not yet widely available.