PPI Calculator: Pixels Per Inch and Pixel Density
Enter your screen resolution and diagonal size to get the pixel density in PPI, the dot pitch in millimetres, the diagonal resolution in pixels, the total megapixels, and the aspect ratio. Switch to the two-screen comparison mode to see which display is sharper. Results update instantly as you type.
What is PPI and how is it calculated?
Pixels per inch (PPI) measures the pixel density of a screen: how many individual pixels fit into one linear inch of display. A higher PPI means smaller, more tightly packed pixels, which produces a sharper image because individual dots become harder to see. The calculation uses the Pythagorean theorem to find the diagonal pixel count from the horizontal and vertical resolution, then divides that by the physical diagonal size in inches. The formula is: PPI = sqrt(width_px^2 + height_px^2) / diagonal_in. For example, a 2560 x 1440 display on a 27-inch panel gives a diagonal of sqrt(2560^2 + 1440^2) = 2943.9 px, divided by 27 = about 109 PPI.
PPI vs. DPI: what is the difference?
PPI (pixels per inch) describes screens and digital images: it counts the physical pixels packed into one inch of a display panel. DPI (dots per inch) is a print-world term: it counts the ink dots a printer lays down per inch. When you read a phone spec sheet, the density figure is always PPI. When you set up a document for print, you work in DPI. The two numbers converge when you print a digital image, but they measure different physical realities. This calculator deals exclusively with PPI for screens and monitors.
Dot pitch and why it matters
Dot pitch is the reciprocal of PPI expressed in millimetres (dot pitch = 25.4 / PPI). It tells you how far apart the centres of two adjacent pixels are. On a 109 PPI monitor the dot pitch is about 0.233 mm. On a 458 PPI iPhone display it is about 0.055 mm. Dot pitch was the primary quality benchmark for CRT monitors, where a 0.28 mm pitch was considered good. For modern LCD and OLED screens, PPI has become the standard comparison figure, but dot pitch still matters for close-up work: a very small dot pitch means the display can render finer detail.
Viewing distance and the Retina threshold
Apple coined the term "Retina display" for screens where pixels are indistinguishable to the human eye at a typical viewing distance. The threshold is roughly 300 PPI at 30 cm (phone use), about 220 PPI at 45 cm (tablet), and around 110 PPI at 60 cm (desktop monitor). This is why a 27-inch 1080p desktop monitor at 82 PPI can look fine from your chair, while the same density on a phone held 25 cm from your face would look noticeably pixelated. PPI is always relative to viewing distance: a 4K TV at 75 inches and 59 PPI looks sharp across a room but coarse up close.
PPI density tiers and typical device types
| PPI range | Density tier | Typical use |
|---|---|---|
| Under 96 | Low (LDPI) | Large format displays, projectors, e-ink readers |
| 96-159 | Medium (MDPI) | 1080p desktop monitors at 24-27 inches |
| 160-239 | High (HDPI) | 1440p monitors, older laptops |
| 240-319 | Extra-high (XHDPI) | 4K monitors at 27 inches, mid-range phones |
| 300+ | Retina threshold | Pixels invisible to the eye at normal distance |
| 320-479 | Extra-extra-high (XXHDPI) | 4K at 21-24 inches, flagship phones |
| 480-640 | Ultra (XXXHDPI) | Current flagship smartphones (iPhone, Galaxy) |
| Over 640 | Beyond XXXHDPI | High-end VR headsets, specialised medical displays |
Based on the Android density bucket system and common industry usage. Viewing distance strongly affects whether higher PPI is perceptible.
Frequently asked questions
What is a good PPI for a monitor?
For a typical desktop monitor viewed from 50-70 cm, 90-110 PPI (a 27-inch 1080p panel) is acceptable, while 109+ PPI (27-inch 1440p) is comfortable and 163 PPI (27-inch 4K) is sharp enough that pixels are invisible at normal desk distances. Laptop screens at 13-15 inches typically range from 150 to 230 PPI, and anything above 200 PPI looks crisp at arm's length.
What PPI do smartphones use?
Modern flagship smartphones typically fall between 400 and 580 PPI. Apple's iPhone line has used 458 PPI (Super Retina XDR) on smaller models and around 460 PPI on Pro models since 2020. Samsung Galaxy S-series displays are in a similar range. Mid-range phones often land between 270 and 400 PPI, which is still comfortably above the 300 PPI Retina threshold for handheld distances.
Does higher PPI always mean a better screen?
Not necessarily. Once PPI exceeds the Retina threshold for your viewing distance, you gain no visible sharpness benefit. Beyond that point, other factors - panel type (OLED vs IPS vs VA), brightness, colour accuracy, refresh rate, and contrast ratio - matter more. Very high PPI at a large size can also increase GPU load for gaming or content creation, since the GPU must render more pixels.
What is the difference between screen resolution and PPI?
Resolution is the count of pixels: 1920 x 1080, 2560 x 1440, 3840 x 2160. PPI is the density of those pixels in physical space. Two monitors can have identical resolution but very different PPI if their panels are different physical sizes. A 24-inch 1080p monitor is 91 PPI, while a 13-inch 1080p laptop screen is 169 PPI, yet both display the same number of pixels.
How do I find my screen resolution and diagonal size?
On Windows, right-click the desktop and go to Display settings; the resolution is shown in the Resolution dropdown. On macOS, open System Settings, go to Displays, and your current resolution is listed. The physical diagonal size is usually printed on the product box, in the manufacturer's specifications page, or embossed on the back of the monitor. Common sizes are 24, 27, 32, and 34 inches for desktop monitors, and 13, 14, 15, and 16 inches for laptops.