PPI Calculator (Pixels Per Inch)
Calculate a display's pixel density from its resolution and diagonal size. PPI tells you how sharp a screen is — the number behind "Retina" claims — and lets you compare a phone, laptop and TV on equal footing.
How to use this calculator
- Enter the screen's horizontal and vertical resolution in pixels.
- Enter the diagonal size in inches (the number screens are marketed by).
- Press Calculate for PPI, dot pitch, megapixels and a sharpness rating.
Formula used
The diagonal in pixels comes from the Pythagorean theorem, then divides by the physical diagonal. Dot pitch is the flip side — millimeters per pixel (25.4 ÷ PPI). Apple's "Retina" marketing roughly means the density where pixels stop resolving at typical viewing distance.
Example calculation
A 27-inch 2560×1440 monitor: diagonal = √(2560² + 1440²) = 2937 px ÷ 27 = 108.8 PPI — standard desktop sharpness.
The same 1440p resolution on a 5-inch phone would be ~587 PPI — over five times denser, which is why phones look sharper than monitors despite lower resolution.
Why PPI matters more than resolution
Resolution alone is misleading — 1080p is crisp on a phone and coarse on a 40-inch TV, because sharpness is pixels packed per inch, not pixel count. PPI captures that by combining resolution and physical size, letting you compare any two displays honestly.
Viewing distance is the hidden variable: a TV watched from three meters needs far lower PPI than a phone held at arm's length to look equally sharp, which is why phones push 400+ PPI while TVs sit near 80 and both look fine. The "Retina" idea formalizes this — above a density threshold at a given distance, the eye can't resolve individual pixels, so more density stops mattering.
Why use this calculator?
- Compare phone, laptop and monitor sharpness on one honest number.
- Judge whether a display is genuinely 'Retina-class' for its use.
- Get dot pitch and megapixels for technical specs and image work.
Frequently asked questions
What is a good PPI for a monitor?
Desktop monitors viewed at arm's length look sharp around 90–110 PPI; 140+ (like 4K at 27") is very crisp. Phones need 300+ because they're held close, while TVs work fine near 80 because you sit far back.
What counts as a Retina display?
Loosely, a density where individual pixels aren't resolvable at typical viewing distance — roughly 300+ PPI for phones held ~30 cm away, but lower for laptops and much lower for TVs. It's distance-dependent, not a single fixed number.
Is higher PPI always better?
Only up to the point your eye can resolve it at your viewing distance — beyond that, extra density adds cost, power draw and GPU load with no visible benefit. Matching PPI to how far you sit matters more than chasing the highest number.