TV Viewing Distance Calculator
For a 65-inch TV, sit between 7 and 9 feet away. Sit too far and you paid for pixels you can't see. Sit too close to a 1080p set and you'll count every one of them.
This calculator uses the THX 36-degree and SMPTE 30-degree viewing angle standards to compute the ideal screen size for your seating distance. It also factors in resolution: 4K lets you sit 1.5x the screen height away before pixel structure becomes visible.
Useful if you're choosing between a 55-inch and 75-inch TV, or deciding whether your couch needs to move before a Sony Bravia 8 II ($1,700) goes on the wall.
How the Viewing Distance Formula Works
The Formula
The calculator converts your seating distance into a recommended screen width using two standards. For THX (36-degree field of view): screen_width = distance x 2 x tan(18°). For SMPTE (30-degree field of view): screen_width = distance x 2 x tan(15°). The width is then converted to a diagonal for 16:9 screens using diagonal = width / cos(atan(9/16)).
Worked Example
At 10 feet (120 inches), the THX factor of 0.6494 gives a screen width of 77.9 inches, which is a 89-inch diagonal. The SMPTE factor of 0.5359 gives 64.3 inches wide, or a 74-inch diagonal. So for a 10-foot viewing distance, your sweet spot is a 74 to 89-inch screen. A 75-inch TV like the LG C4 ($1,800) lands right at the SMPTE minimum.
Standards
THX's 36-degree standard comes from their cinema certification program, targeting the kind of immersive experience you get in a properly designed movie theater. SMPTE's 30-degree recommendation (from the Society of Motion Picture and Television Engineers) is slightly more conservative and better for mixed-use living rooms. The 4K minimum distance of 1.5x screen height comes from the angular resolution limit of human vision at 20/20 acuity.
Limitations
These formulas assume a centered seating position and a flat or very slightly curved screen. If your couch is off-axis by more than 30 degrees, viewing angle on a VA-panel TV matters more than distance. The calculator also assumes 16:9 content. Ultrawide or 2.35:1 projection screens need different math.