What this calculator covers
- The pixel density, in pixels per inch, of any screen from its width and height in pixels and its diagonal size.
- Diagonal in inches, centimeters or millimeters. With centimeters or millimeters you also get pixels per centimeter.
- Screen size presets for laptops, monitors and TVs at standard resolutions, and resolution presets from 720p to 8K.
- Two screens side by side, with the difference in pixel density.
- Widths and heights greater than 0 and up to 1,000,000 px; diagonals greater than 0 and up to 10,000 in the chosen unit.
- The calculator assumes square pixels and treats the number you enter as the diagonal of the picture area.
- Everything runs in your browser. No sign-up, no login, no pop-ups, and nothing is uploaded.
How PPI is calculated
Pixels per inch
Diagonal in pixels = √(width² + height²). For 1920 × 1080 that is √(1920² + 1080²) = 2,202.91 px.
PPI = diagonal in pixels ÷ diagonal in inches. On a 24-inch screen: 2,202.91 ÷ 24 = 91.79 PPI. A diagonal in centimeters is divided by 2.54 first, and one in millimeters by 25.4. Pixels per centimeter = PPI ÷ 2.54.
Dot pitch, pixels and ratio
Dot pitch, the distance between the centers of two neighboring pixels, = 25.4 ÷ PPI in millimeters, or 25,400 ÷ PPI in micrometers.
Total pixels = width × height, and megapixels = total pixels ÷ 1,000,000.
Aspect ratio is the width and height divided by their greatest common divisor. The common ratio is the closest of 1:1, 5:4, 4:3, 3:2, 16:10, 16:9, 21:9 and 32:9, with the difference in percent. The actual ratio is width ÷ height.
Density tier
The density tier is the closest of the screen density buckets listed in the Android developer documentation: ldpi (~120 dpi), mdpi (~160 dpi), hdpi (~240 dpi), xhdpi (~320 dpi), xxhdpi (~480 dpi) and xxxhdpi (~640 dpi). Closest is measured as a ratio: 200 PPI is compared as 200 ÷ 160 = 1.25 with mdpi and 240 ÷ 200 = 1.2 with hdpi, so it goes to hdpi.
Viewing distance
20/20 vision is defined as resolving two points one minute of arc (1′) apart. One pixel spans 1′ at a distance of 1 ÷ (PPI × tan 1′) inches, which is about 3,437.75 ÷ PPI inches. Farther away than that, the spacing between pixels is less than one minute of arc.
Rounding
PPI, pixels per centimeter, the diagonal in pixels and megapixels are shown to 2 decimal places. Dot pitch is shown to 4 decimal places in millimeters and 2 in micrometers, and the viewing distance and ratio difference to 1 decimal place. Each value is rounded to the nearest digit, with halves rounded away from zero. Every result is calculated from the unrounded numbers, and the unrounded PPI is always shown, so the same inputs always give the same answer.
FAQ
How do I calculate the PPI of a screen?
Enter its width and height in pixels and its diagonal size, or pick a preset. For a 24-inch 1920 × 1080 monitor the pixels per inch calculator gives 91.79 PPI.
Why do I sometimes see 92 PPI for a 24-inch 1080p screen?
The exact value is 91.7878 PPI. Rounded to a whole number it is 92, and rounded to 2 decimal places it is 91.79. This page states its rounding and always shows the unrounded value as well.
Can I use it as a screen PPI calculator for phones and tablets?
Yes. Enter the screen resolution in pixels, in portrait or landscape, and the screen diagonal. The ratio and density are the same either way round.
Can I use it as a PPI to DPI converter?
For a screen there is nothing to convert: when a screen density is given in dpi, as in the Android density buckets above, it counts the screen's pixels per inch, so it is the same number as the PPI here. Printer DPI counts ink dots and is a different setting. For the DPI of an image at a print size, use the DPI calculator. To turn a pixel size into a print size, use the pixels to inches converter.
How do I compare two screens?
Press "+ Compare a second screen" and fill in screen B. Both sets of results appear side by side, with the difference in pixels per inch in percent.
Does this calculator upload anything?
No. There is no file upload. You type the numbers and the calculation runs in your browser.