Pixel density from resolution and screen size, with the distance the pixels disappear.
1
What you provide
About 24 in for a desk monitor, 12 in for a phone.
2
Result
108.8 PPI
At 24 inches the pixels remain individually resolvable: 143 PPI would be needed and this panel has 109. Move back to 32 inches and they merge.
Diagnostic telemetry
Pixel density
108.8 PPI
Dot pitchCentre-to-centre spacing of two pixels
0.2335 mm
Panel size59.8 × 33.6 cm
23.5 × 13.2 in
Density needed at 24 in
143 PPI
Pixels invisible beyond80 cm — where individual pixels stop being resolvable
31.6 in
What this cannot tell you
Assumes square pixels and a flat panel measured corner to corner. A curved screen measured along the curve gives a slightly low density.
The "pixels disappear" distance uses 20/20 vision, which resolves about one arcminute. Acuity varies: someone with 20/12 vision resolves nearly twice the detail and will see structure this calculation says is invisible.
Density says nothing about panel quality. Contrast, colour accuracy, response time and coating all affect how a screen looks and none of them appear here.
Subpixel arrangement is not accounted for. Two panels at the same density can render text differently depending on whether they use a standard stripe layout or a pentile-style arrangement.