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PPI Calculator
Get PPI, dot pitch, aspect ratio, and physical screen size from any resolution and diagonal. Free from TestMu AI (Formerly LambdaTest).
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Enter horizontal resolution, vertical resolution, and diagonal size to calculate PPI.
What Is a PPI Calculator?
A PPI calculator is an online tool that computes pixels per inch, the pixel density of a display, from its resolution and diagonal size. Enter width and height in pixels plus the diagonal in inches or centimeters, and it returns PPI, dot pitch, aspect ratio, and physical screen dimensions instantly.
Screens are often described with DPI (dots per inch), a term borrowed from printing, so this TestMu AI tool doubles as a display DPI calculator: the density it returns is the number spec sheets label ppi or dpi. To work out only the shape of a screen, use the Aspect Ratio Calculator.
How Does This PPI Calculator Work?
The calculator reads three values: horizontal resolution, vertical resolution, and diagonal size. If the diagonal is entered in centimeters, it first divides by 2.54, following the 1in = 2.54cm = 96px equivalence table in the W3C CSS Values and Units specification. It then applies the Pythagorean theorem to the pixel grid:
diagonal px = sqrt(width² + height²)
PPI = diagonal px / diagonal inches
Example: 27" QHD monitor (2560 x 1440)
sqrt(2560² + 1440²)
= sqrt(8,627,200)
= 2937.21 px
2937.21 / 27 = 108.79 PPIFrom that density the tool derives everything else: dot pitch is 25.4 / PPI millimeters (the spacing between pixel centers), pixels per centimeter is PPI / 2.54, physical width is the horizontal resolution divided by PPI, and total pixels is width times height. If you only need the length conversion, the CM to Inches converter handles that on its own.
How Do You Use This PPI Calculator?
- Pick a device preset (optional): choose one of 7 presets, from a 24 inch Full HD monitor to the 6.7 inch iPhone 15 Pro Max, or leave Custom to type your own values.
- Enter the resolution: type the horizontal and vertical pixel counts, for example 2560 and 1440.
- Enter the diagonal size: type the panel's diagonal and pick inches or cm in the unit dropdown.
- Read the results: PPI, pixels per cm, dot pitch, diagonal resolution, total pixels, aspect ratio, and physical width and height update on every keystroke, with no button to press.
- Copy, sample, or start over: Copy Results puts a plain text summary on your clipboard, Load Sample fills in the 27 inch QHD example, and Reset clears every field.
All processing happens in your browser. No data is uploaded, and nothing you type is stored after you close the tab.
What Is the Difference Between PPI and DPI?
PPI counts physical pixels on a display, while DPI counts the dots a printer lays down (or a scanner samples) per inch of paper. The two are frequently swapped in everyday language, but they describe different hardware:
| PPI (Pixels Per Inch) | DPI (Dots Per Inch) | |
|---|---|---|
| What it counts | Physical pixels a display packs into one inch of panel | Ink dots a printer places, or samples a scanner reads, per inch of paper |
| Where it applies | Monitors, laptops, phones, tablets, TVs | Printing and scanning |
| How it is fixed | Set by the panel hardware; calculated from resolution and diagonal | Chosen per job in print or scan settings |
| Values you will meet | 91.79 (24 inch 1080p) to 460 (iPhone 15 Pro Max) | Hundreds to thousands of dots per inch, model dependent |
In everyday usage the two blur: spec sheets and OS scaling settings describe screens in DPI even though the physical quantity is pixels per inch. Whichever term you searched for, the math on this page is the one that applies to displays.
Why Does Pixel Density Matter in Web and App Testing?
Web layout does not happen in device pixels. The W3C CSS Values and Units specification defines the CSS pixel so that 1in = 96px, which makes 96 pixels per inch the reference density regardless of the panel's real PPI. On a dense screen, one CSS pixel is drawn with several device pixels.
Browsers expose that gap as devicePixelRatio, the ratio of physical pixels to CSS pixels; MDN describes a value of 1 as a classic 96 DPI display and 2 as the expectation for HiDPI or Retina screens. Check your own screen's live value with the Device Pixel Ratio Checker, and measure your viewport in CSS pixels with What's My Browser Size.
- Asset scaling: a 460 PPI phone renders a 1x image blurry, so srcset and 2x or 3x exports need verification on hardware that actually has that density.
- Device coverage: your users' screens span roughly 92 to 460 PPI, and TestMu AI's real device cloud puts 10,000+ real devices across that range in your browser for manual and automated runs.
- Visual regression: subpixel rounding and image scaling differ between a 1x desktop and a 3x phone, and SmartUI compares screenshots across those configurations to catch the drift.
- Bug reports: attaching resolution, diagonal, computed PPI, and devicePixelRatio to a rendering bug makes it reproducible on the first try.
Frequently Asked Questions
What is a good PPI for a monitor?
Desktop monitors commonly range from 92 PPI (24 inch 1080p) to 163 PPI (27 inch 4K). Near 110 PPI, text and UI render at a comfortable size without OS scaling; a 27 inch QHD panel sits at 108.79 PPI. Higher densities are usually paired with 125 to 200 percent scaling.
What is the PPI of a 27 inch 4K monitor?
A 27 inch 4K monitor (3840 x 2160) has a pixel density of 163.18 PPI. The diagonal resolution is the square root of 3840 squared plus 2160 squared, about 4405.81 pixels, divided by 27 inches. The same panel at 32 inches drops to 137.68 PPI.
What is the PPI of a 24 inch 1080p monitor?
A 24 inch 1080p monitor (1920 x 1080) has a pixel density of 91.79 PPI and a dot pitch of 0.2767 mm. The same Full HD resolution on a 15.6 inch laptop panel is much denser at 141.21 PPI, because the identical pixel grid is packed into a smaller area.
How do I find the PPI of my own screen?
Find your resolution in your OS display settings (for example, System Settings > Displays on macOS or Settings > System > Display on Windows) and the diagonal size on the monitor's spec sheet or model label. Enter all three values above; the calculator reports PPI, dot pitch, and physical dimensions instantly.
What is dot pitch, and how does it relate to PPI?
Dot pitch is the distance between the centers of two adjacent pixels, measured in millimeters. It is the inverse of pixel density: dot pitch = 25.4 / PPI, since one inch equals exactly 25.4 mm. A 27 inch QHD display at 108.79 PPI has a 0.2335 mm dot pitch.
What is PPCM (pixels per centimeter)?
PPCM (pixels per centimeter) expresses the same pixel density as PPI in metric units: PPCM = PPI / 2.54, because one inch equals 2.54 centimeters. A 108.79 PPI monitor is 42.83 PPCM. This calculator reports both, plus physical width and height in inches and centimeters.
Why does my calculated PPI differ from the manufacturer's number?
Manufacturers round the marketing diagonal, which shifts the computed density slightly. Apple's iPhone 15 Pro Max is sold as 6.7 inches, but its tech specs list the rectangle at 6.69 inches; entering 2796 x 1290 at 6.7 gives 459.59 PPI versus the advertised 460 ppi. Differences of 1 to 2 PPI are normal.
Is a higher PPI always better?
No. Beyond the density your eyes can resolve at your viewing distance, extra pixels add GPU load without visible sharpness. Higher resolutions also mean more pixels to render and test. Phones offset extreme densities (400 PPI and up) with device pixel ratios of 2 to 3, so UI elements stay a usable physical size.
Does the DPI value saved in an image file change how it looks on screen?
No. The DPI number stored in an image file is print metadata: it tells a printer how large to render the pixels on paper. On screen, only the image's pixel dimensions and your display's pixel density matter. A 1000 pixel wide image draws identically whether its metadata says 72 or 300 DPI.
What PPI do modern phone screens have?
Modern phone screens are far denser than desktop monitors. The 6.7 inch iPhone 15 Pro Max packs 2796 x 1290 pixels, which Apple's tech specs list as 460 ppi, roughly triple a 27 inch 4K monitor's 163.18 PPI. That density is why phones need 2x and 3x image assets.
Can I calculate screen size from PPI and resolution?
Yes. Rearrange the formula: diagonal inches = diagonal pixels / PPI, where diagonal pixels is the square root of width squared plus height squared. For example, a 2560 x 1440 panel rated at 108.79 PPI works out to 2937.21 / 108.79, which is a 27 inch display.
Is a mouse DPI calculator the same as a PPI calculator?
No. Mouse DPI measures how many counts a mouse sensor reports per inch of physical movement, and gaming eDPI multiplies that by in-game sensitivity. Screen PPI measures how many pixels a display packs per inch of panel. This calculator handles screen density; it does not convert mouse sensitivity.
Is my screen data uploaded when I use this PPI calculator?
No. This PPI calculator runs entirely in your browser with client side JavaScript: the resolution and diagonal you enter never leave your machine, and nothing is stored between sessions. You can verify this by loading the page once and then using the calculator with your network connection disabled.
Enter a resolution and diagonal above to get your numbers in seconds. When a density check turns into a rendering bug, organize the follow up test cases with Test Manager from TestMu AI.
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