TechCompare LogoTechCompare
← Back to Home

PPI & Retina Calculator

Screen A

Pixel Density92 PPI
Retina Distance
37 inches95 cm

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's the fastest way to compare two monitors on equal footing: a 27-inch 1440p panel, a 32-inch 4K panel, and a 24-inch 1080p panel all look very different up close even though their resolutions suggest otherwise.

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 horizontal and vertical pixel counts plus the diagonal in inches, and the calculator returns pixel density in PPI alongside the Retina distance in both inches and centimetres. Add a second screen to get 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 the most-searched monitor, laptop, and TV configurations.

27" 1440p monitor
109 PPI, the mainstream sweet spot
View details ➜
27" 4K monitor
163 PPI, Retina-class at desk distance
View details ➜
32" 4K monitor
138 PPI, 4K at native 100% scaling
View details ➜
24" 1080p monitor
92 PPI, the 1080p baseline
View details ➜
34" 3440×1440 ultrawide
110 PPI, ultrawide productivity default
View details ➜
65" 4K TV
68 PPI, past Retina at living-room range
View details ➜

Resolution comparisons

Side-by-side breakdowns of the resolution choices that share this calculator's URL namespace.

1080p (1920×1080) vs 1440p (2560×1440)
The most common upgrade path for a mainstream desktop monitor.
Read comparison ➜
1440p (2560×1440) vs 4K (3840×2160)
The GPU-cost trade-off that defines most high-end desktop builds.
Read comparison ➜
4K (3840×2160) vs 8K (7680×4320)
The resolution jump where physics finally outpaces human vision.
Read comparison ➜

Frequently asked questions

How do I calculate PPI for a 27-inch 1440p monitor?
Take the diagonal pixel count (sqrt(2560² + 1440²) ≈ 2938 pixels) and divide by the diagonal size in inches. For a 27-inch 1440p display that gives roughly 109 PPI, which is the standard density 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, it's around 160-220 PPI.
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?
Higher PPI means smaller pixels, which only matters if you're close enough to see them. A 4K TV at 3 metres can look identical to a 1080p TV at the same distance because you're already beyond Retina distance for both. PPI should always be judged 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.
What PPI should I look for when buying a monitor?
For productivity and text work, aim for at least 100 PPI, which is roughly 1440p at 27 inches or 4K at 32 inches. Below 90 PPI (like 1080p at 27 inches) text starts to look soft without heavy font smoothing.

Related tools

Screen Size Comparison

Compare screen sizes side-by-side to visualize physical dimension differences.

Use tool ➜

Display Bandwidth Calculator

Check if your HDMI/DP cable supports your resolution and refresh rate.

Use tool ➜

Curved Monitor Visualizer

Visualize monitor curvature radius (1000R, 1500R, 1800R) to see the real curve.

Use tool ➜

FPS Visualiser

Visualise the impact of different FPS settings on your game experience.

Use tool ➜