How Big Should My Screen Be?

How Big Should My Screen Be?

A simple answer might be “how much money do you have?”, but that would ignore the root problem. And it’s not about money, but satisfaction with the result anyway.

The choice of a screen size is actually driven by emotional response. The single most popular screen size in the market today is 42”. That’s where the best prices are, and the 42” set doesn’t demand much from the owner in terms of mounting, or placing on a piece of furniture. In that scenario, the choice is driven only by price and physical size (or lack of it). And that’s the emotion we’re talking about…price and the stress of spending a lot of money on a new TV. That said, it’s funny how many 42” TV owners we hear saying “I wish I’d bought the larger one” though. A 42” screen, as hard as it may be to believe, can have the visual impact of a postage stamp in many homes. In fact, if you’re watching standard TV, an old 4x3 TV will end up with a bigger image on it than the same picture centered on a new 16x9 wide screen 42” TV!

We can separate video screen viewing into two categories: Home Entertainment (casual viewing), and Home Theater (approximate the large, involving image of a theater). Both uses are completely valid, but will result in very different choices.

Home Entertainment screens can be smaller for a couple of reasons. The most obvious is that with this type of use, the viewer doesn’t care about filling his peripheral vision with image, and may not desire to be that involved with the program content. Having a smaller screen separates the view from the content, and isolates him from the “suspension of disbelief” goal of the feature movie maker. Also, smaller screens allow more positional flexibility. You can put smaller screens in a wider variety of places, hang them on smaller mounts, and place them on furniture. So long as we realize the use dictates the size, the Home Entertainment use screen can be 42”, even if the viewer sits 12 feet away.

But that’s not going to work for our other category, Home Theater. If you remove the “Home” qualification from the category title, “Theater” is what remains, and that’s what drives the screen size choice in this world. There are many charts, calculators, and graphs available on web sites that help simplify the process (some are linked below). There has been quite a bit of research into this application, and organizations like SMPTE, THX, and others have specifications that are based on viewing angle with the goal to filling a significant portion of your peripheral vision with picture. We also like to add a resolution parameter to this, since filling your vision with a low resolution image doesn’t do anything to support suspended disbelief.

So the first factor to consider is viewing angle. THX recommends a 36 degree viewing angle, and a minimum of 26 degrees, while SMPTE recommends 30 degrees. For a 50” diagonal screen, that works out to be a viewing distance of 5.6 feet for the recommended THX angle, and 7.9 feet for the THX minimum viewing angle.

Now, let’s look at the same TV from a standpoint of resolution. Assuming a 1080p display, the THX recommended distance will always be slightly closer than the point at which a person with 20/20 vision can no longer see individual pixels. This is because the THX standard is weighted towards favoring peripheral vision rather than resolution, and is actually a pretty smart tradeoff, weighting the entertainment power of a large picture over invisible pixels. (See the post: Can I See 1080p?)

But, as you might begin to see, most TVs purchased are way too small for THX specs. So as you consider screen size and your application, run these numbers to see if you’re in the THX ballpark: Take the screen width (not the diagonal measurement!) and multiply by 1.54. The result is the distance at which you’d need to sit for the optimal THX 36 degree viewing angle. Multiply the screen width by 5, and that’s the maximum recommended viewing distance.

As a closing thought, all of this assumes you are working with a screen aspect ratio of 16x9. These days, that's no longer always true. Technology exists that permits projection of a full 2.35:1 true wide screen image...well beyond this half-baked, slightly narrower than 1.85:1, 16x9 stuff. Oh, don't get me started! But we'll right on that subject soon too.

As always, a professional home theater consultant will be able to optimize your home theater floor plan for screen size and seat position, as well as optimize performance of both your picture and sound.

Links to screen size charts and calculators:
A screen size chart based on resolution
A very nice screen size calculator
Carlton Bale addresses screen size and 1080p