Viewing distance - more info
  1. Small = 20 degree viewing angle. Medium is SMPTE’s 30 degree viewing angle. Large is THX’s “immersive” viewing angle of 40 degrees. More info Source).
  2. If the max screen size class calculation above fits within this viewing distance range, you can feel assured you’ve got the right TV screen size class. This is what should happen in most cases. This also gives you a sense of how big the TV will feel to you within that range.
  3. If the max screen class size is lower than your viewing range, then either you need to move the TV closer to where you’ll view it, or figure out a way to have a bigger TV, such as by mounting it on the wall or buying a larger piece of furniture. If the max is above your range, meaning a TV that may be too big, then you can go with that size if you feel it’ll work for you, or consider buying a smaller TV within the range.
How did you calculate the viewing angles distance multiplication factor?

We can measure the viewing distance from where we sit to our TV. Using this isosceles triangle calculator (meaning the other two angles away from us are the same), we can use the height and vertex angle selection at the bottom of the drop down to calculate the TV screen width for any given viewing distance and viewing angle.

For example, say the viewing distance is 108″ (9 feet x 12 inches/foot), and we want to solve for a 30 degree viewing angle, that gives a TV width (base a) value of 57.87 > 58″. Add an inch on either side for the TV bezel (frame) and that gives us 60″ wide. 60″ x (9/16) = 33.75 > 34″ height. That translates to 68.964 diagonal > 69″ screen class size. 108″/69″ = 1.56 ratio > 1.6, which corresponds with this 1.6x 30 degree Wikipedia/SMPTE ratio too.

  1. 20 degrees = 2.5x (i.e. 108″/2.5 = 43.2″ > 43″ screen class size)
  2. 30 degrees = 1.6x (i.e. 108″/1.6 = 67.5″ > 68″ screen class size)
  3. 40 degrees = 1.2x (i.e. 108″/1.2 = 67.5″ > 90″ screen class size)

Or you use the TV width filters and calculators to bypass this math 🙂