HDTV Size and Distance Calculations
How big should my HDTV be? How far should I be sitting from it? One or both of these questions are usually the toughest
thing consumers are faced with when preparing to buy an HDTV. The simple answer to the first question is, as big as you want
and your budget will allow. The answer to the second question is as close as you can stand it. HDTV was designed to provide
the viewer with a sharper more life-like picture, and it was also designed to occupy a greater portion of your field of view.
Consumers are free to choose whatever size they want, and view the HDTV from any distance they choose; but if you really want
to experience HDTV as intended, the size you choose and the distance you view it from matters!
Most consumers have a difficult time getting their head around how large their new HDTV must be or conversely how close they
must sit to it. For those who are unfamiliar with the topic, you may want to read this basic article
on sizing your HDTV. Much of the confusion surrounding HDTV sizing/viewing distance has to do with the fact that television is
not new, and even though TV technology is evolving, we still want to apply the old rules to that new technology. Adding to the
confusion is that there is no one single standard that everyone agrees on. There is not even complete agreement on one of the
things that most of the standards factor into their recommendations, visual acuity (the limitations of human eye sight).
Back in the good old days (did I just date myself there?), the size of the TV and the viewing distance was pretty
much a personal choice. The resolution that televisions were capable of producing didn’t make the limitations of
human eye sight a factor. Based on the most commonly held theories on human visual acuity, if you possessed 20/20
vision you could view standard cable TV broadcasts on a 27” TV from as far back as 14 feet without missing the minutest
detail. In a standard 12 x 16 foot family room, by the time you account for the 2 foot depth of the set, another 6
inches or so of clearance between the TV and the wall, and another foot for the combined depth of the back of the couch
and your head, you could place the set anywhere in the room without diminishing the picture quality. Now mind you, the
interlaced scanning used with analog television makes even still images a little blurry, but when you combine this with
the limited resolution and add movement in the images, you could effectively watch television from an even greater
distance without any reduction in your viewing experience.
HD television is a quantum leap forward from what most consumers have experienced with television. Even for consumers
who own extended definition tubes or rear projection big screens capable of displaying all the resolution that digital
cable could offer, HDTV is a big step. The transition to HDTV with regards to the set size/viewing distance would be
easier for consumers to accept if HDTV was introduced only at a 720p resolution and had stayed at that resolution for
20 years or so before 1080p was introduced.
To get your head around the radical change in set size/viewing distance you have to understand two things; pixel count
and the limitation of the human eye to resolve detail. The effective pixel count of a very good analog TV is 204,800
(512 x 400) pixels. Standard definition digital TV (SDTV), whether displayed in the 4:3 format like analog TV or the 16:9
format has a count of 355,200 (704 x 480) pixels. If an analog TV and digital TV sets are the same size and dimensions,
the increased pixel count of digital TV means that each pixel has to be smaller than on the analog TV. The good news is
the smaller pixels make the image you see crisper and more realistic. The bad news is smaller objects are tougher to see
from a distance, which brings our ability to see and resolve detail into the picture.
The ability to resolve the details of objects (generally referred to as visual acuity), has been studied by scientists
for over 100 years. The measurements of our ability to see fine detail is defined in degrees, just like a circle. Defining
our ability to see in that manor removes the issue of how far away we are from the object we are trying to make out.
If you think of an open ended triangle that stretched out to infinity and a vertical line of fixed length that crossed
the two sides of the triangle. As you move the point where the two side of the triangle meet away from the vertical line,
eventually the vertical line will no longer cross the two sides of the triangle. With regards to our ability to see detail,
once an object can no longer touch the two lines of the triangle, we can’t make out the detail. The most widely accepted
belief is that a person with “normal” vision can resolve detail down to as small as 1/60 of 1° of a circle; some
believe that we can resolve detail a little smaller than 1/120 of 1° of a circle. Whatever the limit is, the
important thing to remember is if it is too small we can’t see it.
The more pixels that make up a picture, the sharper the image will appear. So to provide us with a better picture,
HDTV increases the count of pixels used in the display. With our ability to see detail fixed, we have to move closer
to the image or make the image bigger once we pass the threshold of our visual acuity to see all the detail. With 1080p
HD resolution being the choice of consumers buying televisions today, the 2,073,600 (1920 x1080) pixels that makes up its
display, is 10 times the count of the pixels of analog TV. So we are not taking about a little change but a major overhaul
of the size of our TV and/or the viewing distance. That is why the recommendations for HDTV size and the distance you
should sit from them seem so outlandish, a lot has changed. For the interior designer (real or a voice inside your head),
who is telling you, “you don’t want a TV that big in the room because it will dominate the room”, SHHHHH!; or you can listen
to that voice and diminish your television viewing experience.
There are many recommendations to be found on the topic of TV size and viewing distance, the most commonly quoted are the
SMPTE and THX recommendations, and the manufacturer / retail recommendation (diagonal measurement of the screen size times
2.5 to get your seating distance) . Less quoted recommendations are those based purely on visual acuity or the design
goals of HDTV. If you want to figure out the size and/or viewing distance from your HDTV, we have created an HDTV size/viewing
distance calculator which is located at the bottom of this page. Although there are many viewing distance calculators already
available on the web (some better than others), we have re-invented the wheel so to speak, to address their short comings. Some
of the calculators are difficult to use even if you have knowledge of the topic, and the better ones are geared towards the
construction of a home theater with multi-row seating. Since most buyers of HDTVs are not constructing a multi-row home theater,
some of their recommendations are inappropriate where HDTV is concerned. In addition to the raw data, we also present relevant
background information with regard to the theories behind the numbers.
Based on your responses, which were: