About this tool
The TV Size & Viewing Distance Calculator is a free, in-browser tool that answers the two questions people ask before buying a television: what screen size fits my seating distance, and how far should I sit from a TV I already have. It bases the answer on field-of-view standards and your resolution, since 4K sets let you sit closer than 1080p without seeing pixels. Everything runs locally in your browser, so nothing you enter is uploaded.
The tool uses distance-to-diagonal ratios. For 4K/UHD the comfortable range is distance ≈ diagonal × 1.0 to 1.5 (optimal around 1.2, close to the THX cinematic angle); for 1080p it is distance ≈ diagonal × 1.5 to 2.5 (optimal around 2.0, near the SMPTE 30° mixed-use angle). In find-size mode it inverts this to recommend a diagonal from your distance and snaps it to the nearest common size (32/43/50/55/65/75/85 in). In find-distance mode it returns a comfortable minimum-to-maximum distance range for your diagonal. It also reports the horizontal viewing angle, 2 × atan((0.436 × diagonal) / distance), using a 16:9 screen width of 0.872 × diagonal.
As a worked example, a 9 ft (108 in) seating distance on a 4K TV suggests a diagonal of about 108 / 1.2 ≈ 90 in, snapping to an 85 in set, with a comfortable range of roughly 72–108 in. Going the other way, a 65 in 4K TV has an optimal distance near 65 × 1.2 ≈ 78 in (6.5 ft) and a comfortable range of about 5.4–8.1 ft. Personal preference matters — cinephiles sit closer for a more immersive angle, while casual viewers sit a bit farther back.