How is the result calculated?
Based on the horizontal viewing angle: ideal screen width = 2 × viewing distance × tan(half the viewing angle), then the width is converted to a diagonal in inches based on the standard screen ratio (16:9). A 30° angle represents the minimum comfortable size (SMPTE standard), and a 40° angle represents the immersive cinematic experience (THX standard, developed by Lucasfilm).
What's the difference between the SMPTE and THX standards?
SMPTE is more conservative and aims for eye comfort over long viewing periods (minimum viewing angle of 30°), while THX aims for an immersive, cinema-like experience where the screen fills more of your peripheral vision (36°-40° angle). The range between the two limits is both acceptable and comfortable, and the choice depends on your priority.
Does the calculation differ between a TV and a computer monitor?
The formula is the same, but the viewing distance differs drastically: a TV is usually 2-4 meters away, while a computer monitor is usually only 50-90 cm away, producing much smaller sizes despite using the same comfortable viewing angles.
Does screen resolution (4K, for example) change the result?
Higher resolution allows sitting closer to a larger screen without noticing individual pixels, but it doesn't change the eye's own comfortable viewing angle. This calculator gives you the general visual comfort range regardless of the specific screen resolution.
What if my actual screen size is larger or smaller than the recommended range?
A screen smaller than the minimum means you're not benefiting from the full detail (especially with high-resolution content). A screen larger than the recommended maximum may cause eye strain or the need to move your head/eyes a lot to follow the whole picture — this can usually be solved by increasing the viewing distance slightly instead of shrinking the screen.
