PPI Calculator (Pixel Density)
Enter your resolution and diagonal screen size to get PPI (pixels per inch) and pixel pitch. See how tightly packed your pixels are compared with other devices, side by side.
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| Device | Common PPI range | Typical viewing distance |
|---|---|---|
| Phone | 300–500 | 10–14 in (25–35 cm) |
| Tablet | 220–330 | 14–18 in (35–45 cm) |
| Laptop | 120–250 | 20–28 in (50–70 cm) |
| Desktop monitor | 80–185 | 20–31 in (50–80 cm) |
| Living-room TV | 40~90 | 5–10 ft (1.5–3 m) |
Note: PPI is calculated from the active display area. Manufacturers often round the advertised diagonal, so a real product can differ from this result by roughly 1–3 PPI. Marketing terms such as "Retina" have no single fixed PPI — the threshold changes with the device and how far away you sit. Treat these numbers as a reference.
How to use it
How to use this PPI calculator
PPI stands for pixels per inch — how many individual pixels are packed into one linear inch of screen. A higher number means finer detail, because each pixel is physically smaller. This calculator turns two numbers you can look up in any spec sheet, resolution and diagonal size, into PPI and pixel pitch.
Three steps
- Enter the resolution. Use the native (maximum) resolution, not whatever your operating system is currently scaled to. A 27" 4K monitor is 3840 × 2160 even if Windows is displaying it at 1920 × 1080.
- Enter the diagonal size in inches. This is the number in the product name — the 27 in "27-inch monitor". Measure corner to corner across the glass, not including the bezel.
- Read the result. You get PPI, pixel pitch in millimetres, and a zoomed grid comparing your screen against a phone, a laptop and a 4K monitor.
The formula
PPI is the diagonal resolution divided by the diagonal size. You need Pythagoras to get the diagonal in pixels first:
PPI = √(width² + height²) ÷ diagonal inches
Take a 27-inch 4K monitor at 3840 × 2160. The diagonal in pixels is √(3840² + 2160²) = √(14,745,600 + 4,665,600) = √19,411,200 ≈ 4405.6 pixels. Divide by 27 and you get about 163 PPI.
Pixel pitch is the flip side — the physical width of one pixel. Since there are 25.4 mm in an inch, pitch = 25.4 ÷ PPI. At 163 PPI that is 25.4 ÷ 163 ≈ 0.156 mm per pixel.
Why viewing distance changes everything
PPI on its own is a poor way to compare screens, because you do not hold them all at the same distance. A phone sits roughly 12 inches from your eyes; a desk monitor about 24 inches; a living-room TV 6 to 10 feet away.
What actually matters is angular density — pixels per degree of your field of view. A person with 20/20 vision can resolve detail about one arcminute apart, which works out to roughly 60 pixels per degree. Past that threshold, extra pixels are invisible.
That is why a 55-inch 4K TV at 80 PPI can look flawless from the sofa while a 400 PPI phone screen still shows text edges if you hold it two inches from your face. The rough rule: every time you double the viewing distance, you can halve the PPI and see the same amount of detail.
What counts as high PPI in 2026
- Phones: 400–500 PPI is standard. Flagships push past 500, which is mostly beyond what the eye resolves at normal holding distance.
- Tablets: 250–300 PPI. Held slightly farther away than a phone, so the lower number looks equally sharp.
- Laptops: 100–120 PPI for a 1080p 15-inch panel; 200+ for a high-resolution 13- to 14-inch display.
- Desktop monitors: a 27" 1440p panel is about 109 PPI; the same size at 4K is about 163 PPI. Both are common, and both are fine — they just need different scaling.
- TVs: 40–80 PPI. Low by phone standards, but you sit far enough away that it does not matter.
The scaling trap on high-PPI monitors
Once a desktop display goes much above 140 PPI, text rendered at 100% becomes uncomfortably small, so the operating system scales the interface up. macOS does this cleanly at 2× on displays built for it. Windows lets you pick 125%, 150% or 175%, and some older applications still render blurry at fractional scaling.
This is why 27" 4K (163 PPI) can feel awkward while 32" 4K (138 PPI) is often more comfortable — the larger panel is usable without scaling at all. If you want a sharper image without touching scaling settings, a bigger 4K panel is usually the easier choice.
What "Retina" actually means
It is a marketing term, not a fixed number. Apple introduced it with the iPhone 4 in 2010, describing roughly 300 PPI at a holding distance of about 10 to 12 inches as the point where individual pixels stop being distinguishable. Because the threshold depends on distance, the PPI required to qualify differs for a watch, a phone, a laptop and a desktop display. There is no single Retina PPI value.
Frequently asked questions
Is PPI the same as DPI?
They get used interchangeably, but they describe different things. PPI is pixel density on a screen. DPI (dots per inch) is how many ink dots a printer lays down per inch. When you are talking about displays, PPI is the correct term; DPI belongs to print, where 300 DPI is the usual standard for photo-quality output.
Is more PPI always better?
No. Past the point where your eye can resolve individual pixels at your normal viewing distance, extra density buys you nothing visible — but it still costs GPU performance and battery life, because there are more pixels to draw every frame. A 4K phone screen is a good example of density with no practical payoff.
My calculated PPI does not match the manufacturer spec. Why?
Advertised diagonals are usually rounded. A panel sold as 27" might actually measure 27.0 or 26.9 inches of active display area, which shifts the result by one to three PPI. Some listings also quote the outer dimensions rather than the visible area. A small discrepancy is normal.
What resolution should I enter if my screen is scaled?
Always the native resolution — the panel's physical pixel grid. Scaling changes how large things appear, not how many pixels exist. If you enter a scaled resolution you will get a PPI figure that describes nothing physical.
How do I work out pixel pitch from PPI?
Divide 25.4 by the PPI, because an inch is 25.4 mm. At 109 PPI the pitch is about 0.233 mm; at 163 PPI it is about 0.156 mm. Smaller pitch means the pixel grid is harder to see up close. Pixel pitch is the figure usually quoted for LED video walls, where it is measured in millimetres rather than PPI.
Two screens have the same PPI but look different. What is going on?
Beyond distance, panel technology plays a part. Subpixel layout matters — a standard RGB stripe renders text more crisply than a PenTile arrangement at the same nominal PPI. Anti-glare coatings scatter light and can soften fine detail, and contrast affects how sharp an edge appears even when the pixel count is identical.
What size should a 4K monitor be?
For desk use, 27" 4K gives about 163 PPI — very sharp, but you will want display scaling turned on. 32" 4K works out to roughly 138 PPI, which many people find comfortable at 100%. If you would rather not deal with scaling at all, 32 inches is the safer pick.