Free screen PPI calculator. Enter resolution and diagonal size to get pixels per inch, dot pitch, megapixels, and a plain-English sharpness verdict.
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PPI (pixels per inch) measures how densely pixels are packed on a display: more pixels per inch means sharper text and finer detail. Find it in two steps. First, compute the diagonal resolution in pixels with the Pythagorean theorem: diagonal pixels = sqrt(width² + height²⁾. For a 1920x1080 screen that is sqrt(1920² + 1080²⁾ = 2,202.9 pixels. Second, divide by the physical diagonal size in inches: 2,202.9 / 24 = 91.79 PPI. The dot pitch, the physical distance between pixel centers, is 25.4 / PPI millimeters (25.4 mm = 1 inch), so 91.79 PPI gives a 0.277 mm dot pitch. One nuance: PPI alone does not decide perceived sharpness, because viewing distance matters. A phone held 30 cm from your face needs far higher density than a monitor at arm's length, which is why 92 PPI looks fine on a desktop monitor but would look coarse on a phone.
Every PPI calculation does the same two things. Step one: find the diagonal resolution in pixels using the Pythagorean theorem, because a screen's resolution is given as width by height, not as a diagonal. Step two: divide that pixel diagonal by the physical diagonal in inches.
Worked example for a 1920x1080 monitor at 24 inches: 1. Diagonal pixels = sqrt(1920² + 1080²⁾ = sqrt(3,686,400 + 1,166,400) = sqrt(4,852,800) = 2,202.9 pixels. 2. PPI = 2,202.9 / 24 = 91.79 pixels per inch. 3. Dot pitch = 25.4 / 91.79 = 0.277 mm.
If you only know the physical width and height in inches, there is an equivalent form: PPI = sqrt((width_px² + height_px²⁾ / (width_in² + height_in²⁾⁾. Same answer, different route.
Enter the screen's resolution in pixels: width first, then height. A 4K monitor is 3840 by 2160; a 1440p monitor is 2560 by 1440. Then enter the diagonal size in inches, the number on the box or spec sheet: 24, 27, 15.6, 6.1, whatever it is. Measure the screen itself, not the bezel, if you are checking a spec you do not trust.
The calculator returns the PPI, the dot pitch in millimeters, the total pixel count in megapixels, the diagonal resolution in pixels, and a plain-English sharpness verdict. Find your resolution in your operating system's display settings if you do not know it: on Windows it is under Display settings, on macOS under Displays, on Android and iOS in the device's published specifications.
Good depends on the device and how far you sit from it. Rough bands used across the industry:
- 400+ PPI: ultra high density. Premium smartphones and VR headsets (iPhone 15 Pro: 460). - 250-400 PPI: high density. High-end tablets and laptops (iPad Pro 12.9: 264, MacBook Pro 14: 254). - 175-250 PPI: Retina-class. MacBooks and high-res monitors where pixels dissolve at normal distance. - 100-175 PPI: standard density. Normal desktop monitors and laptops (4K at 27 in: 163, 1440p at 27 in: 109). - Below 100 PPI: low density. Large 4K TVs viewed from the couch (55 in 4K: 80) and basic monitors (1080p at 24 in: 92).
Per-use guidance: text-heavy work (code, documents) feels best at 150+ PPI, photo and video editing at 200+ PPI for true detail at 100% zoom, and gaming is comfortable from about 100 PPI up. For general desktop use, anything above 100 PPI at arm's length is comfortable, 110 looks clean, and 140+ looks very sharp.
PPI alone does not decide whether you see pixels; viewing distance does. Human vision resolves detail down to about one arcminute of angle, so a pixel becomes invisible once it is small enough relative to how far away it is. Apple built the Retina concept on this: the same panel can be Retina at one distance and visibly pixelated at another.
That is why a phone needs 400+ PPI (you hold it 25 to 30 cm from your face) while a monitor is crisp at 140 PPI (you sit 60 to 80 cm away) and a 4K TV is perfectly fine at 80 PPI (you watch from 2 to 3 meters). Apple's 3438 rule captures it: multiply the viewing distance in inches by 3438 and divide by the PPI to estimate the distance at which pixels dissolve for normal vision.
Practical baselines for a desktop monitor at arm's length: about 90 PPI is the usable baseline rather than a crisp one, 110 looks clean, and 140-plus is very sharp. You do not need phone-class numbers on a screen you sit back from, which is exactly why 27-inch 4K (163 PPI) is the sweet spot for many desk setups.
PPI (pixels per inch) describes screens: how many image pixels fit in one inch of display. DPI (dots per inch) describes printers: how many ink dots land on one inch of paper. They measure related ideas in different worlds and are not interchangeable.
For screens, PPI comes from the formula on this page. For print, 300 DPI remains the gold standard for sharp photos, flyers, and documents; 150 DPI is enough for posters viewed from a distance, and 600 DPI suits fine art and barcodes.
One more number to know: CSS defines a reference pixel at 96 PPI. Web layouts assume 96 pixels per inch regardless of the physical screen, which is why a 200 px box looks the same physical size on a 92 PPI monitor and a 460 PPI phone, even though the phone renders it with far more physical pixels. High-DPI web design handles the gap with responsive images (srcset) and the devicePixelRatio value in JavaScript.
Sanity-check your result against these widely published figures:
- iPhone 15 Pro (2556x1179, 6.1 in): 460 PPI - iPad Pro 12.9 (2732x2048, 12.9 in): 264 PPI - MacBook Pro 14 (3024x1964, 14.2 in): 254 PPI - iMac 24 (4480x2520, 23.5 in): 218 PPI - 27-inch 4K monitor (3840x2160): 163 PPI - 27-inch 1440p monitor (2560x1440): 109 PPI - 24-inch 1080p monitor (1920x1080): 92 PPI - 55-inch 4K TV (3840x2160): 80 PPI
Notice the pattern: the same 4K resolution gives 163 PPI on a 27-inch monitor and 80 PPI on a 55-inch TV. Resolution alone says nothing about sharpness; size completes the picture. If your calculated number lands far from the published figure for a known device, double-check that you entered the screen diagonal, not the outer dimensions of the device.
The most common monitor dilemma. At 27 inches, 4K (3840x2160) gives 163 PPI: genuinely sharp text, crisp UI, Retina-like at about 21 inches of viewing distance. 1440p (2560x1440) gives 109 PPI: the long-standing sweet spot for gaming and productivity, clean at normal desk distance but not in the same league for text.
The trade-off is GPU load. A 4K screen has 8.29 megapixels to push every frame versus 3.69 for 1440p, more than double the work. For competitive high-refresh gaming, 1440p with a mid-range GPU usually beats 4K with the same card. For creative work, code, and reading, 4K's sharper text wins and the GPU matters less.
The 27-inch 1080p option (82 PPI) is the budget pick: pixels become visible in text at normal distance, so reserve it for secondary screens or tight budgets.
A 3840x2160 monitor with a 27-inch diagonal: 1. Diagonal pixels = sqrt(3840² + 2160²⁾ = sqrt(14,745,600 + 4,665,600) = sqrt(19,411,200) = 4,405.8 pixels. 2. PPI = 4,405.8 / 27 = 163.18 pixels per inch. 3. Dot pitch = 25.4 / 163.18 = 0.156 mm. 4. Megapixels = 3840 × 2160 / 1,000,000 = 8.29 MP.
Verdict: standard density, fine for everyday desktop use, and sharp enough that most people stop noticing pixels at normal desk distance. Compare with 1440p at the same size: sqrt(2560² + 1440²⁾ = 2,938.5 pixels / 27 = 108.79 PPI, dot pitch 0.233 mm, 3.69 MP.
Find the diagonal resolution in pixels with the Pythagorean theorem, then divide by the screen's diagonal size in inches: PPI = sqrt(width² + height²⁾ / diagonal. For 1920x1080 at 24 inches: sqrt(1920² + 1080²⁾ = 2,202.9, divided by 24 = 91.79 PPI.
Most modern phones sit between 400 and 500+ PPI, well above the point where the human eye can see individual pixels at typical holding distance. Anything above roughly 300 PPI looks perfectly sharp on a phone; above 400 is flagship territory.
For desktop use at arm's length: 100-175 PPI is standard and comfortable, 140+ looks very sharp, and 150+ is ideal for text-heavy work like code and documents. Photo and video editors should aim for 200+ PPI to judge true detail. Gaming is comfortable from about 100 PPI up.
It depends on viewing distance, which is the whole point of Apple's Retina concept: pixels dissolve when each one subtends about one arcminute of your vision. As a rule of thumb, about 300 PPI qualifies at phone distance, while about 200 PPI already looks perfectly sharp on a laptop viewed from farther away.
PPI (pixels per inch) is for screens: how many image pixels fit in one inch of display. DPI (dots per inch) is for printers: how many ink dots land on one inch of paper. Use this calculator for screens; for print sizing, 300 DPI remains the standard for sharp output.
For web design, the CSS standard assumes 96 pixels per inch. That is a definition for consistent layouts, not a measurement: physical screens vary widely, from about 80 PPI on large TVs to 460 PPI on flagship phones. Use 96 PPI as your baseline for web design, and the formula on this page for physical density.
Dot pitch (or pixel pitch) is the physical distance between the centers of adjacent pixels, in millimeters: 25.4 / PPI. A 91.79 PPI screen has a 0.277 mm dot pitch; a 163.18 PPI screen has 0.156 mm. Smaller dot pitch means finer detail.
No. Beyond the point where pixels dissolve at your viewing distance, extra density buys nothing visible while costing GPU performance, battery life, and money. A monitor does not need phone-class PPI because you sit farther from it. Match density to distance and use case instead of maximizing the number. The raw figures only matter relative to how far you sit.
91.79 PPI. Diagonal pixels = sqrt(1920² + 1080²⁾ = 2,202.9, divided by 24 = 91.79. Dot pitch is 0.277 mm. That is standard desktop density: fine for everyday use, with pixels slightly visible in small text.
163.18 PPI. Diagonal pixels = sqrt(3840² + 2160²⁾ = 4,405.8, divided by 27 = 163.18. Dot pitch is 0.156 mm and the panel holds 8.29 megapixels. Noticeably sharper text than 1440p at the same size (108.79 PPI).
Resolution: on Windows open Display settings, on macOS open Displays in System Settings, or check the manufacturer's spec page. Size: use the diagonal printed on the box or spec sheet, measuring the screen itself rather than the bezel. Common laptop sizes are 13.3, 14, 15.6, and 16 inches.
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