Pixel Density Calculator: PPI Calculator, Pixels Per Inch
Pixel Density Calculator. Enter your Width, Height and Diagonal in this pixel density calculator to get your screen's PPI. The pixel pitch calculator is designed for commercial and large-format displays where pixel pitch in millimetres is the primary specification.
Interactive Tool
Input Resolution
The width and height fields are used only when “Physical width and height” is selected.
Results
Plug in your width and height in pixels (or pick a preset like 1080p or 4K), and this pixel density calculator shows you the total pixels, megapixels, aspect ratio, and how your resolution stacks up vs 1080p and vs 4K.
Two screens can share the same resolution and still look nothing alike, and the pixel density calculator tells you why. Enter the resolution of the display plus its diagonal, and you get pixels per inch (PPI), pixels per centimeter (PPCM), dot pitch and megapixels in one pass. A higher PPI packs more detail into every inch, so text and images look sharper. Every result assumes square pixels, which almost every modern panel uses.
What Pixels Per Inch Measures on a Screen
Pixel density is the number of pixels that fit along a one-inch line on a physical surface. Because a pixel has no size of its own, PPI only makes sense for something with a fixed physical size: a monitor, a phone screen, a printed page. A digital image sitting in a file has a resolution (say 3072 × 1920) but no PPI until it is shown or printed, since zooming changes how big each pixel appears. To calculate your ppi, enter your screen diagonal in inches and your resolution — the tool computes it instantly.
Resolution and pixel density are related but not the same. Resolution counts the pixels; PPI tells you how tightly the pixel grid is packed. Put the same 1080p resolution on a 13-inch notebook display and a 25-inch monitor and the smaller screen wins on image quality, because each pixel is smaller and individual pixels are harder to see. That is why display technology marketing leans on pixels per inch, and why you should always compare each monitor or display at its native resolution.
How to Calculate PPI From Resolution and Screen Size
To calculate PPI you need three numbers: the width in pixels, the height in pixels and the diagonal in inches. The PPI formula works in two steps, and the diagonal you use should be the viewable area of the display, not the bezel-to-bezel size printed on the monitor box. The burn in test is particularly useful for checking gaming displays that have been used with static HUD overlays.
$$\text{PPI} = \frac{\sqrt{w_p^{2} + h_p^{2}}}{d_i}$$
Diagonal in Pixels With the Pythagorean Theorem
A screen is a rectangle, so its width, height and diagonal form a right triangle. The Pythagorean theorem gives the diagonal in pixels from the horizontal pixels and vertical pixels:
$$d_p = \sqrt{w_p^{2} + h_p^{2}}$$
This diagonal resolution is then divided by the diagonal in inches, \(\text{PPI} = d_p \div d_i\). Because pixels are square, PPI comes out the same whether you measure across, down or along the diagonal.
Pixels Per Square Inch and Total Pixels
Two more outputs come from the same inputs. Total pixels is simply width × height, often shown in megapixels (millions of pixels). Pixels per square inch measures density over an area instead of a line, and it is the PPI squared: \(\text{PPI}^{2}\). A panel at 250 PPI therefore holds about 62,500 pixels in every square inch, which is why small gains in PPI feel bigger than the number suggests.
Worked Example With the Pixel Density Calculator
Here is a full run on a 14.5-inch laptop display with a 3072 × 1920 resolution, a 16:10 shape rather than the more common 16:9. Every figure below was computed from the formulas above.
Entering Screen Resolution and Diagonal Screen Size
- Type the screen resolution: 3072 for width and 1920 for height.
- Type the diagonal screen size: 14.5 inches (36.83 centimeters).
- The diagonal works out to √(3072² + 1920²) = √13,123,584 ≈ 3,622.65 pixels.
- Divide by the diagonal: 3,622.65 ÷ 14.5 ≈ 249.84 PPI.
If you only know the diagonal in centimeters, enter that instead and the pixels per centimeter result comes out directly; the pixels per inch figure follows by multiplying by 2.54.
Reading the Results and Comparing a Second Screen
| Result | Value |
|---|---|
| Pixel density | 249.84 PPI (98.36 PPCM) |
| PPI² | 62,419 |
| Pixel total | 5,898,240 (5.90 MP) |
| Dot pitch | 0.1017 mm |
| Aspect ratio | 8:5 (16:10) |
| Retina distance | 13.8 inches (35.0 cm) |
Run the pixels per inch calculator again for a rival 16-inch display at 2560 × 1600 and you get 188.68 PPI. The 14.5-inch display is about 32% denser, so its text looks visibly crisper at the same distance. A side-by-side run like this is the fastest way a PPI calculator settles which screen is actually sharper.
Dot Pitch, PPCM and Aspect Ratio
The same three inputs also give you the metric density and the shape of the screen. Divide PPI by 2.54 to get PPCM, the unit most metric spec sheets use.
Dot Pitch in Millimeters
Dot pitch is the distance from the center of one pixel to the center of the next, the inverse of PPI converted to millimeters:
$$\text{dot pitch (mm)} = \frac{25.4}{\text{PPI}}$$
For the 249.84 PPI example that is 0.1017 mm, or a pixel pitch of about 101.7 µm. Dot pitch was the headline spec in the CRT era, when a quarter of a millimeter between pixels was easy to picture; today PPI has mostly replaced it because modern values are so small.
Aspect Ratio in Lowest Terms
The aspect ratio is width to height reduced to lowest terms. Find the greatest common factor of both numbers and divide: the GCF of 3072 and 1920 is 384, so the ratio is 8:5, usually written 16:10. As a single number it is 1.6:1. The calculator needs the ratio of the resolution and the physical display to match, otherwise the PPI result is off.
Retina Distance and Viewing Distance for Monitor PPI
A high PPI only helps if you sit close enough to notice it. The human eye resolves fine lines down to roughly 1 arcminute (1/60 of a degree) with normal visual acuity. Beyond that point, neighbouring pixels blur together and the screen looks smooth; this is the idea behind Apple's retina display label.
The retina distance follows from that angle:
$$\text{distance (in)} \approx \frac{3438}{\text{PPI}}$$
For the 249.84 PPI notebook that is about 13.8 inches, so at a normal 18-22 inch viewing distance you will never see a pixel. Check monitor PPI the same way: a 34-inch 2560 × 1080 ultrawide at about 82 PPI needs roughly 42 inches before it stops showing pixels, so sharpness at a desk depends as much on distance as on resolution.
Choosing Between Two Desk Monitors With the PPI Formula
The decision: a photo retoucher with a shallow desk wants to know which of two shortlisted monitors will look pixel-free from where they actually sit. The short answer is that the 28-inch 4K panel clears the bar with room to spare, while the 23.8-inch 1440p panel misses it by a quarter of an inch.
First, the one number nobody puts on a spec sheet: eye-to-screen distance. With a tape measure from the bridge of the nose to the panel surface, it comes to 27.6 inches. Solving the retina rule backwards gives the density needed at that distance: 3438 ÷ 27.6 ≈ 124.6 PPI. Anything above that line looks smooth; anything below it can show a pixel grid on fine text.
Next, both candidates go into the calculator, resolution first and then the diagonal:
| Monitor | Diagonal in pixels | Pixels per inch | Pixel-free from |
|---|---|---|---|
| 23.8 in, 2560 × 1440 | 2,937.21 | 123.41 | 27.86 in |
| 28 in, 3840 × 2160 | 4,405.81 | 157.35 | 21.85 in |
I recomputed both by hand (√(2560² + 1440²) ÷ 23.8, then 3438 ÷ 123.41) and the figures match. The 23.8-inch screen needs the viewer 27.86 inches away, so at 27.6 inches it sits 0.26 inch inside the zone where pixels can show. That near-miss is the number to watch, because a slight lean forward while masking hair detail makes it worse.
Two caveats change the picture. The 3438 constant assumes 1 arcminute, roughly 20/20 vision; someone with sharper 20/15 eyesight resolves about 0.75 arcminute, which raises the requirement at 27.6 inches to 166.1 PPI, and then neither monitor passes. And the 4K screen will almost certainly run at 150% scaling, so interface elements are drawn at an effective 104.9 pixels per inch; the pixel density of photos at 100% zoom stays at 157.35, which is what retouching cares about.
The sensitivity rerun settles it: if the desk were deeper and the distance grew to 30 inches, the 1440p panel would clear the line too. At 27.6 inches it doesn't, so the 28-inch 4K monitor is the one to buy.
How Dots Per Inch Differs on Printers and Cameras
Dots per inch (DPI) sounds like PPI, and on a screen the two match, but in printing they measure different things, and printing is where mixing them up costs you. A printer lays down tiny ink dots of a few fixed colours and blends them to fake each pixel's colour, so its DPI is usually much higher than the PPI of the image it prints.
PPI vs DPI on Screens and Paper
The practical difference in PPI vs DPI shows up when you move an image between devices. The pixel count stays fixed, so the print size sets the PPI: a 3072-pixel-wide image printed 10 inches wide lands at 307 PPI, while the same file stretched to 30 inches drops to about 102 PPI. A common rule of thumb is to keep image PPI at half the printer's DPI or less, so a 600 DPI printer is well served by a 300 PPI file. Graphics meant only for the web don't need printing-level PPI; a monitor shows them at its own pixels per inch regardless.
Subpixel Layouts, PenTile and Camera View Screens
- Each screen pixel is built from red, green and blue subpixels, so one pixel is really three dots.
- PenTile layouts share subpixels between pixels, so the perceived sharpness of the display is lower than the PPI suggests.
- A camera spec of "dots" on its view screen counts every colour dot: divide by 3 to get true pixels before you work out its PPI.
- On a scanner or in photography sensor specs, PPI describes sampling density, not the screen PPI this calculator returns.
PPI Categories From LDPI to XXXHDPI
Mobile platforms group screens into density buckets so apps can scale their layouts. Use the table to place any result from the calculator, from low density panels on large TV sets to the high density screens on a flagship smartphone.
| Bucket | Approx. PPI | Scale factor |
|---|---|---|
| ldpi | ~120 | 0.75x |
| mdpi | ~160 | 1x |
| hdpi | ~240 | 1.5x |
| xhdpi | ~320 | 2x |
| xxhdpi | ~480 | 3x |
| xxxhdpi | ~640 | 4x |
The example notebook display at 249.84 PPI sits just above the hdpi line. A 43-inch 4K tv lands near 102 PPI, under mdpi, which is fine at couch distance.
Logical DPI on Android
These buckets are logical DPI values, not exact measurements. Android rounds a phone's real pixel density to the nearest bucket and scales icons and text by that factor, so two phones at 401 and 458 PPI may both render as xxhdpi. That makes the PPI result from the calculator a direct way to predict which bucket, and which asset scale, a given phone will use.
When to Use a PPI Calculator Before Buying
Reach for a PPI calculator when the resolution alone doesn't settle the choice: an ultrawide against a 16:9 monitor, 1440p against 4K at a given size, or whether a 5K or 8K panel is worth the price at your distance.
Gaming and Productivity Monitor Needs
- Gaming: about 100-140 PPI on the monitor is enough; refresh rate and response time usually matter more than extra pixels, which cost frame rate.
- Productivity: aim for 140 PPI or more on a desktop display for text clarity during long reading sessions; a 25-inch 1440p screen gives about 117 PPI.
- Photo editing and content creation: 180+ PPI lets you judge small edits at 100% zoom on the display without leaning in.
- Phone and notebook screens: viewed closer, so they need far higher pixels per inch than a desktop monitor or a living-room display.
Scaling and Common Misconceptions
- Higher PPI is not always better: past the point your eye can resolve, a 4K or 8K monitor makes you pay in GPU load for pixels you can't see.
- Low PPI shows as pixelation and staircasing on curves and small fonts, and font smoothing can only hide part of it; a 1080p panel at 27 inches is the classic case.
- High-PPI screens rely on OS scaling (150% or 200%) so text isn't tiny; plan for it when you compare one monitor against another.
- Pixels look magnified on a large display only when you sit too close, so pair this tool with a screen size calculator to check the physical fit.
Frequently Asked Questions
- How do I calculate PPI from the screen diagonal?
- Find the diagonal in pixels with the Pythagorean theorem, √(width² + height²), then divide it by the diagonal in inches. A 3072 × 1920 screen has a 3,622.65-pixel diagonal, so at 14.5 inches it has 249.84 PPI.
- How do I calculate PPI if I know the screen's width and height instead of the diagonal?
- Divide the horizontal pixel count by the physical width in inches (or the vertical count by the height). With square pixels both give the same PPI. You can also add the squares of the physical width and height and take the square root to get the diagonal, then use the usual formula.
- What is a good PPI for a monitor?
- For text-heavy work, around 140 PPI or more at a normal desk distance keeps text crisp, while about 100-140 PPI is usually enough for gaming. Photo editing benefits from 180 PPI or more. What counts as good always depends on how far away you sit.
- What is retina distance and how is it calculated?
- It is the distance beyond which a person with normal vision can no longer see individual pixels, based on a 1 arcminute limit. In inches it is roughly 3438 divided by the PPI, so a 249.84 PPI screen looks pixel-free from about 13.8 inches.
- Does a higher PPI always mean a sharper image?
- Only if you sit close enough to see the difference. Once you are past the retina distance, extra pixels add GPU load and cost but no visible sharpness, so judge PPI together with viewing distance.
- Why does the same resolution look sharper on a smaller screen?
- The same number of pixels is packed into less space, so each pixel is smaller and the PPI is higher. A 1920 × 1080 panel has about 151.9 PPI at 14.5 inches but only 88.1 PPI at 25 inches.
- Is PPI the same as DPI?
- On a screen they are used interchangeably, because each pixel is one dot. In printing, DPI counts the ink dots a printer lays down, which is usually much higher than the PPI of the image being printed.