How to Find the Right Size TV

As larger screen TVs continue to drop in price and higher screen resolutions become available, it can seem difficult to make a buying decision and be confident in your choice. While the recent increases in screen resolutions and sizes, such as 4K and 8K, will have benefits for some, they may have little to no benefit for others. The key is to understand how screen size, viewing distance, and optimum screen resolution are connected. With this knowledge, choosing the proper sized HDTV for a particular setting becomes an easy task and one that you can confidently complete.

Why Bigger is Usually Better

Screen sizes have increased steadily over the last two decades. In 2000, the average TV screen was just 27 inches, but these days 55-inch TVs are quite common and prices for larger screens are continuing to fall.

“Buy the biggest TV you can afford” is an often heard piece of advice. Indeed, many people who are first skeptical and even buy an HDTV they think is too big, later wish they had gone for an even bigger model. Large HDTV screens are surprisingly easy to get used to.

Putting space and budget restrictions aside, which size HDTV would be considered ideal? We looked for advice from two authorities on the subject – THX (they do more than produce rumbling cinema trailers) and SMPTE (The Society of Motion Picture and Television Engineers).

THX vs SMPTE Viewing Angle

THX recommends that the ideal screen should fill 40 degrees of the viewer’s field of vision. This does not sound like much at first, considering humans have almost 180 degrees peripheral vision and a stereoscopic field of view of around 100 degrees. However, given the average viewing distance is 9 feet, this would mean at TV would have to have a screen diagonal of 90 inches to meet this criteria. This seems very large compared to today's average screen sizes but might well be a sign of things to come. Vary large HDTV screens provide a more immersive viewing experience, more akin to a cinema or IMAX screen.

SMPTE instead recommends a viewing angle of 30 degrees. While this is less than the recommendation from THX, it would still require a TV with a 68” inch diagonal screen when viewed from 9 feet away.  This is a more practical and economical sized display for most folks.

However, following THX or SMPTE guidelines, bigger really is almost always better. If you can afford it, go for a larger screen as it’s unlikely you will ever feel that the HDTV you bought is too big unless your susceptible to motion sickness while watching somebody play video games.

Screen Resolution and Human Vision

Before looking at how to choose the right screen resolution, it is worth understanding a bit about human vision.

The amount of detail a human eye and brain can process is limited.  A person with normal vision, also referred to as 20/20 vision, can usually differentiate pixels taking up 1/60 of a degree of the field of vision. This might vary depending on the circumstances, such as if the pixels have a very high contrast, but this figure serves as a useful guide.

Screen Resolution Comparison

For a screen of a fixed size and resolution this means there will be a viewing distance where each pixel of the screen covers 1/60 degree of the viewer’s vision. If the viewer moves further back, the viewing angle will reduce and each pixel will take up less of the viewer’s filed of vision. There will be no further improvement in the screen’s perceived image quality as the human eye will no longer be able to process the increased pixel density. If the viewer moves closer to the screen, individual pixels will become more noticeable as the number of pixels per angle decrease.

TV Viewing Distance Chart

The above chart shows the optimum viewing distances for popular HDTV screen resolutions such as 4K, Full HD and 720p HD.

Let’s assume your living room space is limited and you sit 8 feed away from the TV. What size and resolution would be ideal? The horizontal line indicating 8 feet (2.4m) on the chart intersects with the line representing ‘720p HD optimum viewing distance.’ Moving vertically down from the intersection, it can be seen that the recommended screen size for 720p resolution is just over 40 inches, so a 42-inch TV with 720p resolution would match those criteria perfectly. A smaller TV or increasing the viewing distance would not increase the perceived sharpness of the image. Moving closer or a larger screen size would decrease the perceived resolution below the ideal of 60 pixels per angle. In this case a higher resolution HDTV would be required for the best image quality. Moving along the 8 feet viewing distance horizontal line, we can see it intersects with the line representing ‘1080p optimum viewing distance’ at a screen size of around 63 inches. This is already within SMPTE’s recommended viewing angle of 30 degrees and probably a good compromise between choosing a large screen without the added expense of 4K resolution.

To fulfill THX’s recommendation of a 40-degree viewing angle, an 80-inch TV with 4K resolution would be required. While this would be ideal for a cinema-like experience, 1080p resolution is a great choice when looking for a reasonable screen size for a competitive price.

Conclusion

The last piece of advice in this article is to not worry too much about any of the advice. Let this be a guide that helps you choose the proper size HDTV, but know that the world won't end and you won't lose your sanity if your system doesn't quite fit THX or SMPTE recommendations, or if your display should be a higher resolution according to the above graph. Personal preference, living space restrictions, and of course price, should also be factored in when making a decision. What are your thoughts on HDTV screen size? Let us know in the Audioholics forum.