How to determine if you can benefit from a 4K display

[Dusso Janladde]

Before I explain the math behind it, I'll sum it up:

Measure your viewing distance in inches. To get any benefit from a 4K display, the diagonal size of the display needs to be greater than half the viewing distance. To get the full benefit of 4K, the diagonal size of the display needs to be about equal to the viewing distance.

This is all based on pixels per degree. A person with average visual acuity (20/20 vision) can see about 80 pixels per degree. A display with fewer pixels per degree will be bad as you'll be able to distinguish the individual pixels, while a display with more pixels per degree is also bad as you won't be able to see all the detail. Pixels per degree depends on three things: Resolution, screen size, and viewing distance.

To better understand this, let's use a 60" TV as an example. Starting with the lowest resolution, 480p, you would see 80 pixels per degree at 23.3 feet away. At this distance, any resolution higher than 480p would look no better. However, if you were to move closer, you would start to be able to distinguish the individual pixels of a 480p image, and it would look worse and worse as you got closer, while higher resolutions would look better and better.

When you reach 17.8 feet from the TV, you would now be able to see all the detail in a 720p image - you would be seeing 80 pixels per degree. However, 1080p and anything higher would still look the same as 720p. Continue to move closer and you'll start to be able to distinguish the pixels of a 720p image and it will start to look worse and worse. Higher resolutions will still continue to look better and better.

When you reach 10.3 feet away, you'll be seeing the full benefit of 1080p at 80 pixels per degree, but higher resolutions such as 4K will still look the same as 1080p. Note that the viewing distance in this case is 123 inches, almost exactly twice the screen size of 60 inches.

And, likewise, if you get even closer, 1080p will start to look bad. 4K would still look better and better, until you get to just 4.9 feet away (that's 58.7 inches). That's almost the same as the screen size of 60 inches.

So, basically, in order to get any benefit from 4K, you need a bigger screen and/or you need to sit closer. If you have a huge projection screen, say 170", you would get the full benefit of a 4K projector at 13.9 feet, and the full benefit of 1080p at 33.3 feet.

The calculator I used for all this can be found here. All calculations were made for a 16:9 screen, with 3840x2160 for 4K resolution.