Screen Resolution Converter

PPI (Pixels Per Inch) measures how sharp a screen appears. Higher PPI means more detail and smoother text.

Formula: PPI = √(width_px² + height_px²) ÷ diagonal_inches

The diagonal in pixels is calculated using the Pythagorean theorem. Then divided by the physical screen diagonal in inches.

DPCM (Dots Per Centimeter):

• DPCM = PPI ÷ 2.54

Common device PPI values:

Those PPI figures come from the manufacturers, who quote a nominal diagonal. The real panel is usually a hair smaller than the round number on the box, so calculating from “6.1 inches” gives 461 PPI where Apple publishes 460. A point or two of disagreement between a spec sheet and this calculator is the diagonal being rounded, not an error.

Sharpness guidelines:

• Under 100 PPI: visible pixels at arm’s length
• 100–150 PPI: standard desktop monitors
• 150–250 PPI: “Retina” quality at normal viewing distance
• Over 300 PPI: print-quality sharpness (smartphones)

Retina distance. There is a way to make “Retina” a number rather than a marketing word. A person with 20/20 vision resolves about one arcminute of angle, so pixels blur together once a single pixel subtends less than that. Work it backwards and the distance where a screen goes seamless is roughly 3438 ÷ PPI inches. A 92 PPI desktop monitor needs about 37 inches of distance, which is why a normal 24-inch monitor at arm’s length looks fine. A 460 PPI phone gets there at 7.5 inches, closer than anyone holds a phone. That single number explains why a phone, a laptop and a TV need wildly different pixel densities to look equally sharp.

The fact to internalize is that 4K has four times the pixels of 1080p, not two. The names refer roughly to the horizontal pixel count, but doubling both width and height quadruples the total, which is why 4K is 8.3 megapixels against 1080p’s 2.1. That squaring is also why each step up demands so much more from a graphics card, and more bandwidth to stream.

Resolution alone doesn’t equal sharpness, though. What the eye perceives is pixel density (PPI), which depends on the resolution and the screen size together: a 4K phone looks razor-sharp while a 4K 85-inch TV spreads the same pixels over far more area, so it looks less sharp up close. The marketing labels are loose as well, with “2K” and “4K” used a bit inconsistently, so the actual width-by-height figure is the number to trust over the nickname.