Screen PPI Calculator
Find the pixel density of a monitor, phone or tablet from its resolution and diagonal size, and see the matching dot pitch. This page is about screen density - for the effective resolution of an image at a print size, use the Print PPI Calculator.
How it works
PPI is the diagonal pixel count divided by the diagonal size in inches: PPI = √(width² + height²) ÷ diagonal. Dot pitch is the physical distance between pixels: 25.4 ÷ PPI millimetres.
When to use this calculator
- Comparing monitors before buying, beyond resolution alone.
- Checking whether a phone or tablet display is genuinely "Retina" at normal viewing distance.
- Understanding why two 27-inch screens with the same resolution can look different.
- Estimating dot pitch when planning UI sizes or viewing text comfort.
Worked examples
- 1920 × 1080 on 24 inches: the diagonal is about 2203 px, giving roughly 92 PPI and a 0.28 mm dot pitch.
- 2560 × 1440 on 27 inches: about 109 PPI - noticeably sharper than the 1080p example.
- 3840 × 2160 on 32 inches: about 138 PPI, a common sweet spot for 4K desktop work.
- 1080 × 2400 on a 6.5-inch phone: about 403 PPI, comfortably in Retina territory.
PPI, DPI and viewing distance
PPI belongs to screens; DPI belongs to printers. The reason a 400 PPI phone looks sharper than a 92 PPI monitor is not only the number: the phone is held about 30 cm away while the monitor sits 60–80 cm away. Apple's Retina rule of thumb reflects this - around 300 PPI at phone distance, 218 PPI at laptop distance and 150–180 PPI at desktop distance all appear similarly sharp.
What dot pitch tells you
Dot pitch is the physical distance between pixel centres, in millimetres. Lower values mean a finer image. At 92 PPI the pitch is 0.28 mm, at 138 PPI it is 0.18 mm, and at 400 PPI it is 0.06 mm. For office work, anything around 90–110 PPI is comfortable; for detailed design work, 140 PPI and above is preferable.
Common mistakes
- Assuming a higher resolution always means a sharper screen, while ignoring screen size and seating distance.
- Confusing PPI with total resolution: a 4K TV has the same resolution as many monitors but far lower PPI.
- Comparing phone PPI numbers between brands without checking that both measurements use the same diagonal convention.
- Applying screen PPI values to print work, where DPI and physical print size are what matter.
Related tools
Print PPI calculator · Retina image calculator · Aspect ratio calculator
Frequently asked questions
What is the difference between PPI and DPI?
PPI describes pixels inside a digital image or screen. DPI describes dots a printer places on paper. They are often used interchangeably when discussing print resolution, but for displays PPI is the correct term.
What PPI is considered "Retina"?
Apple calls a display Retina when its pixel density is high enough that the eye cannot distinguish individual pixels at a typical viewing distance - roughly 300 PPI on a phone, 218 PPI on a laptop and 150-180 PPI on a desktop monitor.
Does higher PPI always mean a sharper image?
Within reason, yes. But a high-PPI screen with a low-resolution source image can look soft, and at very high densities the eye may not notice the difference from a normal viewing distance.