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PPI Calculator & Retina Distance

PPI = √(width² + height²) ÷ diagonal, with width and height in pixels and the diagonal in inches. A 27-inch (69 cm) 2560 × 1440 monitor has 2937 pixels along its diagonal, so it has 109 PPI. Enter any resolution and size below for PPI and Retina distance, or compare two screens.

Screen A

Resolution presets

Pixel Density82 PPI
Retina Distance
107 cm42 inches42 inches107 cm

Add a second screen to see the sharpness difference side-by-side, pixel grid for pixel grid.

Same 40 × 20 mm of Screen, at Real Pixel Density

This simulation shows an identical 40 × 20 mm (1.57 × 0.79 inch) physical patch magnified at native pixel resolution. It demonstrates how typography and curves render across different screen densities.

Standard 24-inch 1080p92 PPI · 145×72 px

Standard desktop baseline with noticeable pixel staircasing on fine text.

1920×1080 at 27″82 PPI · 128×64 px

Standard desktop density. Pixelation is visible on small fonts and curved lines.

Diagonal physical size: 27 inches (68.6 cm)
Native resolution: 1920 × 1080

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How to use this tool

  1. Enter the screen resolution

    Type the horizontal and vertical pixel counts of the display, like 2560 × 1440 for a 1440p monitor or 3840 × 2160 for a 4K TV. The calculator uses both numbers to compute the diagonal pixel count.

  2. Enter the diagonal size

    Type the screen's diagonal in inches. This is the viewable diagonal, not the bezel-to-bezel external measurement, so a monitor sold as 27-inch class usually gets 27 entered here.

  3. Read the PPI and Retina distance

    The calculator returns PPI (pixels per inch) plus the Retina distance in inches and centimeters. Sit further than the Retina distance and your eye can no longer resolve individual pixels, so the screen looks pixel-perfect.

  4. Add a second screen to compare

    Fill in the second display's resolution and diagonal to get a side by side sharpness comparison with the exact PPI percentage difference. Useful when weighing a 27-inch 1440p panel against a 32-inch 4K panel.

About this tool

The PPI & Retina Calculator works out the pixel density of any display from its resolution and diagonal size, and tells you the minimum viewing distance at which the screen becomes "Retina", the point where the human eye can no longer resolve individual pixels.

It lets you compare monitors on equal footing: a 24-inch 1080p panel, a 27-inch 1440p panel, and a 32-inch 4K panel all look different up close, and resolution alone doesn't tell you by how much.

Use it when you're shopping for a monitor or laptop, deciding how far to sit from a new TV, or designing UI that has to stay legible across a mix of screens. Enter the pixel counts and the diagonal in inches to get PPI and the Retina distance in inches and centimeters. Add a second screen for a side by side sharpness comparison with the exact percentage difference.

Formula

PPI is the diagonal pixel count divided by the diagonal screen size: PPI = sqrt(width² + height²) / diagonalInches. Retina distance (in inches) is approximately 3438 / PPI, which comes from the 1 arc-minute visual-acuity threshold commonly used in display engineering.

When to use it

Reach for this tool whenever resolution alone isn't telling you the full story, such as when comparing ultrawides against 16:9 panels, sanity-checking whether a 4K TV is worth it at your sofa distance, or confirming that a phone upgrade actually delivers a sharper screen in practice.

It pairs naturally with the Display Bandwidth Calculator (to verify your cable can drive the resolution) and the Screen Size Comparison tool (to see the physical difference at scale).

Popular PPI scenarios

Pre-computed pixel density and Retina distance for common monitor and TV configurations.

27" 1440p monitor
109 PPI, a mainstream QHD size
View details
27" 4K monitor
163 PPI, Retina-class at desk distance
View details
32" 4K monitor
138 PPI, sharp text at desk distance
View details

Resolution comparisons

Side-by-side breakdowns of common resolution choices.

27-inch 1440p vs 32-inch 4K
The 32-inch 4K screen packs 27% more pixels per inch, 138 PPI against 109 PPI on the 27-inch 1440p screen.
Read comparison
1080p (1920×1080) vs 1440p (2560×1440)
At 27 inches, 1440p reaches 109 PPI and 1080p reaches 82 PPI, which is 33% more pixels per inch.
Read comparison
1440p (2560×1440) vs 4K (3840×2160)
4K draws 2.25 times the pixels of 1440p each frame, and reaches 163 PPI against 109 PPI at 27 inches.
Read comparison

Frequently asked questions

How do I calculate PPI for a 27-inch 1440p monitor?
Take the diagonal pixel count (sqrt(2560² + 1440²) ≈ 2937 pixels) and divide by the diagonal size in inches. For a 27-inch 1440p display that gives roughly 109 PPI, which is typical for a mainstream QHD monitor.
What is considered a high PPI or Retina display?
A display is considered Retina-class when, at the intended viewing distance, a human eye can no longer resolve individual pixels (about 1 arc-minute of visual angle). On a phone that's roughly 300+ PPI. On a typical desktop monitor viewed from 60-80 cm, the 1 arc-minute formula gives roughly 109-146 PPI. The exact threshold depends on viewing distance and visual acuity.
What is Retina distance and how is it calculated?
Retina distance is the minimum viewing distance at which the human eye can no longer distinguish individual pixels. Using the 1 arc-minute threshold, the distance in inches is approximately 3438 divided by the display's PPI. Sit further than that value and the screen looks pixel-perfect.
Does higher PPI always mean a sharper image?
Not always. Higher PPI means smaller pixels, which only matters if you're close enough to see them. A 4K TV at 10 feet (3 meters) can look identical to a 1080p TV at the same distance because you're already beyond Retina distance for both. Judge PPI together with viewing distance.
Why does the same resolution look sharper on a smaller screen?
Because the pixels are packed into a smaller area. A 24-inch 1080p monitor has about 92 PPI while a 27-inch 1080p monitor only has about 82 PPI, so the 24-inch version shows noticeably crisper text and images even though both are the same resolution. Use the screen size comparison to see the physical difference between those panels side by side.
What PPI should I look for when buying a monitor?
For productivity and text work, aim for at least 100 PPI. A 27-inch 1440p monitor has about 109 PPI and a 32-inch 4K monitor about 138. Below 90 PPI (like 1080p at 27 inches) text starts to look soft without heavy font smoothing.

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