PPI Calculator
Calculate pixel density (PPI), dot pitch, total megapixels and aspect ratio from your screen resolution and diagonal size. Find out if a display qualifies as "Retina".
Common device pixel densities
What is PPI (pixel density)?
PPI stands for pixels per inch — a measure of how tightly packed the pixels are on a display. A higher PPI means more pixels in the same physical space, which produces sharper text and smoother images. It is calculated from the diagonal pixel count and the diagonal screen size:
PPI = √(width² + height²) ÷ diagonal (inches)
Dot pitch is the inverse idea — the physical distance between pixels, expressed in millimetres. Lower dot pitch means a denser, sharper screen.
The "Retina" threshold is Apple's marketing term for a display whose pixels are too small to be distinguished by the human eye at a typical viewing distance. There is no single fixed number, but as a rule of thumb roughly 300 PPI for phones held ~10 inches away, ~220 PPI for laptops, and ~150–220 PPI for desktop monitors viewed further back. This tool flags densities at or above 300 PPI as "Retina-class".
Frequently asked questions
How do I calculate PPI?
Find the diagonal resolution using the Pythagorean theorem — the square root of (width² + height²) — then divide it by the diagonal screen size in inches. For example, a 1920×1080 display on a 24-inch screen: √(1920² + 1080²) ÷ 24 ≈ 2202.9 ÷ 24 ≈ 91.8 PPI.
What is a good PPI for a monitor?
For desktop monitors viewed at arm’s length, 90–110 PPI (typical of 1080p and 1440p panels) is comfortable, while 140–220 PPI ("HiDPI"/Retina) gives noticeably crisper text. Phones and tablets are held closer, so they need 300+ PPI to look equally sharp.
What is dot pitch and how is it related to PPI?
Dot pitch is the physical distance between the centres of adjacent pixels, usually in millimetres. It is simply the inverse of pixel density: dot pitch (mm) = 25.4 ÷ PPI. A 100 PPI screen has a dot pitch of about 0.254 mm.
What counts as a "Retina" display?
Retina is Apple’s term for a screen dense enough that individual pixels can’t be resolved by a normal eye at the intended viewing distance. It depends on distance, but ~300 PPI for phones, ~260 for tablets, and ~220 for laptops are common thresholds. This tool labels results at or above 300 PPI as Retina-class.
Does higher PPI always mean a better screen?
Not necessarily. Beyond the point where the eye can no longer distinguish pixels, extra density adds little visible benefit while increasing power draw and GPU load. Colour accuracy, brightness, contrast and refresh rate often matter more than raw PPI once you pass the Retina threshold.