Displays / Resolution
Screen PPI Calculator
Calculate a screen's pixel density (PPI), dot pitch, physical width and height, and the distance at which pixels blend together, from its resolution and diagonal size.
Screen PPI Calculator: Pixels per inch is the number of pixels along the diagonal, found with the Pythagorean theorem, divided by the diagonal in inches. Dot pitch is its reciprocal in millimetres, and the width and height follow from the aspect ratio. A 27-inch QHD monitor (2560 × 1440) has 108.8 PPI; at 27 inches with 4K (3840 × 2160), it is 163.2. Runs 100% locally in your browser with zero server file uploads.
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The last figure is the viewing distance at which one pixel spans one arcminute, about the finest detail a person with 20/20 vision can see; from farther away, individual pixels can no longer be made out.
Choosing a monitor size and resolution
For a desk, 24 inches at 1920 × 1080 gives about 92 PPI, 27 inches at 2560 × 1440 about 109, and 27 inches at 4K about 163. Operating systems scale text at higher densities, so 4K at 27 inches is usually run at 150% to look like 1440p with sharper detail.
Check a new screen for dead pixels and uniformity with the monitor test, and compare shapes with the aspect ratio calculator.
Screens and print
Printed photos look sharp at about 300 dots per inch held at reading distance, which is why print sizes are worked out differently from screens; the image DPI checker shows how large an image will print.
How to use it
- Enter the resolution in pixels and the diagonal size, or choose a common screen.
- Read the pixel density, dot pitch, and physical size.
- Compare the viewing distance at which pixels blend together with how far you sit.
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Frequently asked questions
What PPI is sharp?
It depends on distance. At a desk 60–70 cm away, about 110 PPI looks fine and 160 or more looks crisp; phones held at 30 cm need 300 or more for pixels to vanish.
Is PPI the same as DPI?
PPI describes pixels on a screen; DPI properly describes dots of ink from a printer, though the terms are often mixed up.
Why does my phone's stated PPI differ slightly?
Makers round the diagonal, and some screens have rounded corners, so the published figure can differ from this calculation by a few PPI.
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