Screen PPI Calculator

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Walk-through

How to Use This Calculator

4 steps

1

Enter your resolution

Type the screen's horizontal and vertical resolution in pixels — for example 2560 by 1440 for a standard QHD monitor. You'll find this in your display settings, or in the product's spec sheet.

2

Enter the diagonal size

Type the screen's diagonal size in inches — the number manufacturers advertise, like '27" monitor' or '6.1" phone'. It's measured corner to corner, not the width or height alone.

3

Read the PPI, dot pitch, and pixel count

The PPI tab updates instantly with the pixels-per-inch value, the dot pitch (the physical distance between pixel centers), total pixel count, and a sharpness tier from Standard to Ultra-high.

4

Check retina status at your viewing distance

On the Retina Check tab, enter how far you actually sit from or hold the screen. The calculator tells you whether individual pixels are visible at that distance, and how it compares to common displays.

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Reference

Formula & Methodology

3 formulas

Pixels per inch (PPI)

PPI = √(width² + height²) ÷ diagonal

The diagonal resolution in pixels — found with the Pythagorean theorem from the horizontal and vertical pixel counts — divided by the screen's diagonal size in inches. A 2560×1440 display on a 27" screen works out to about 109 PPI; the same resolution panel at a smaller diagonal produces a higher PPI, since the same number of pixels is packed into less physical space.

Dot pitch

dot pitch (mm) = 25.4 ÷ PPI

Dot pitch is the physical distance between the centers of two adjacent pixels, in millimeters. It's the inverse of PPI, converted from inches to millimeters (25.4mm per inch) — so as PPI goes up, dot pitch shrinks. A 109-PPI display has a dot pitch of about 0.233mm.

Retina threshold

threshold PPI = 1 ÷ (2 × tan(0.5 × 1/60°) × distance)

This is the standard 1-arcminute angular-resolution model: the human eye generally can't distinguish two points closer together than about 1/60th of a degree of its field of view. Solving that angle for a given viewing distance gives the PPI at which pixels become individually invisible. The closer you view a screen, the higher its PPI needs to be to clear this threshold — a phone held 10" away needs roughly 344 PPI, while a monitor at 24" only needs about 143 PPI.

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Glossary

Key Terms Explained

7 terms

PPI Pixels per inch — the density of a screen's pixels, calculated from its resolution and diagonal size. Higher PPI generally means a sharper, more detailed image.

DPI Dots per inch — the print equivalent of PPI, describing how densely a printer places ink dots on paper. The terms are often used interchangeably in casual speech, but PPI is the correct term for a digital display.

Dot pitch The physical distance between the centers of two adjacent pixels, usually measured in millimeters. Smaller dot pitch means pixels are packed more tightly together, which generally corresponds to a sharper image.

Pixel density Another name for PPI — how many pixels are packed into each inch of physical screen space. It depends on both the resolution and the physical size of the display.

Diagonal resolution The total number of pixels measured along the screen's diagonal, found with the Pythagorean theorem from the horizontal and vertical pixel counts. It's the numerator in the PPI formula.

Retina display A colloquial term (popularized by Apple, now used generically) for a screen dense enough that individual pixels aren't visible to the naked eye at a typical viewing distance. What counts as 'retina' depends entirely on how far away you view the screen.

Viewing distance How far your eyes typically are from the screen — held distance for a phone, arm's length for a monitor, across the room for a TV. It's the key variable in whether a given PPI counts as 'retina'.

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Scenarios

Real-World Examples

3 worked examples

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Shopper comparing two monitors

PPI tab — 1440p vs 4K at the same 27" size

Resolution 2560×1440 Diagonal size 27"

A 2560×1440 monitor at 27" comes out to about 109 PPI — a 'Sharp' tier display. The same 27" panel at 4K (3840×2160) jumps to about 163 PPI, noticeably crisper for text and fine detail, which is why 4K monitors read as sharper even at the same physical size.

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Laptop shopper checking Retina claims

Retina Check tab — MacBook Air 13" at typical laptop distance

Resolution 2560×1664 Diagonal size 13.6" Viewing distance 20"

At about 224 PPI, this display clears the roughly 172-PPI retina threshold for a 20" laptop-typical viewing distance with plenty of margin — individual pixels are not visible under normal use, matching Apple's own Retina marketing for this model.

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Someone checking a phone's sharpness

Retina Check tab — a phone held at arm's length

Resolution 2556×1179 Diagonal size 6.1" Viewing distance 12"

At about 461 PPI, this phone clears the roughly 287-PPI threshold for a 12" hold distance by a wide margin — well into 'retina' territory, which is standard for modern flagship phones held close to the eye.

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Deep Dive

PPI in One Step

3 chapters · 4 min read

"Is this screen sharp enough?" usually gets answered with a raw resolution number — 1080p, 1440p, 4K — that doesn't actually say much on its own, because the same resolution looks completely different on a 24" monitor versus a 6" phone. Pixels per inch (PPI) is the number that actually answers the sharpness question, and this calculator gets you there from the two specs you already have: resolution and screen size.

Resolution alone doesn't tell you sharpness

A 3840×2160 (4K) resolution sounds impressive, but stretched across a 65" TV it works out to only about 68 PPI — plenty sharp from across a living room, but visibly pixelated up close. The same resolution on a 27" monitor is about 163 PPI, sharp enough to read fine text comfortably at a desk. PPI normalizes resolution against physical size, which is why it's the number product reviewers and spec sheets actually cite when talking about sharpness.

What 'retina' really means

'Retina' isn't a fixed PPI number — it's a relationship between pixel density and how far away you view the screen. The human eye can resolve detail down to roughly 1 arcminute of its field of view, and that angular limit translates to a different PPI threshold depending on viewing distance: about 344 PPI for a phone held 10" from your face, but only about 143 PPI for a monitor sitting 24" away. That's why a 461-PPI phone and a 163-PPI monitor can both legitimately claim to be 'retina' for their typical use — they're each clearing the threshold for how close you actually hold them.

Dot pitch and megapixels — the physical picture

Dot pitch flips PPI into a physical measurement: the actual distance, in millimeters, between one pixel's center and the next. It's most useful for comparing displays built on genuinely different pixel technologies, where a smaller dot pitch generally means a more refined image up close. Total megapixels — just the resolution's pixel count divided by a million — is a separate, size-independent number worth knowing for its own reasons: it's what determines file size for a full-resolution screenshot or how much a GPU has to render every frame, regardless of how physically large or small the screen is.

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Questions

Frequently Asked Questions

6 questions

What is PPI?+

PPI stands for pixels per inch — a measure of how densely packed a screen's pixels are. It's calculated as the diagonal resolution in pixels divided by the screen's diagonal size in inches. Higher PPI means a sharper, more detailed image.

What's the difference between PPI and DPI?+

PPI (pixels per inch) describes digital screens. DPI (dots per inch) describes printers and printed output. The two terms are often used interchangeably in casual conversation, but PPI is the technically correct term for a monitor, laptop, or phone display.

What is dot pitch?+

Dot pitch is the physical distance between the centers of two adjacent pixels, measured in millimeters. It's the inverse of PPI: dot pitch (mm) = 25.4 ÷ PPI. A smaller dot pitch means pixels are packed closer together.

What does 'retina display' mean?+

A display is commonly called 'retina' when its pixels are packed densely enough that the human eye can't distinguish individual pixels at a normal viewing distance. The exact PPI needed depends on how far you sit or hold the screen — a phone held close needs a much higher PPI than a TV viewed from across a room.

Is a higher PPI always better?+

A higher PPI generally means a sharper image, but the benefit shrinks once a display exceeds the retina threshold for its typical viewing distance — at that point your eye can no longer tell the difference, and the extra pixels mainly cost more graphics processing power and battery life.

How do I find my screen's resolution?+

On Windows, check Settings → System → Display. On macOS, check System Settings → Displays. On a phone, search the model name plus 'specs' — the resolution and screen size are always listed together.

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Display Specs

How to Use This Calculator

Enter your resolution

Enter the diagonal size

Read the PPI, dot pitch, and pixel count

Check retina status at your viewing distance

Formula & Methodology

Key Terms Explained

Real-World Examples

Shopper comparing two monitors

Laptop shopper checking Retina claims

Someone checking a phone's sharpness

PPI in One Step

Resolution alone doesn't tell you sharpness

What 'retina' really means

Dot pitch and megapixels — the physical picture

Frequently Asked Questions

Get a branded PDF of your results

Screen PPI Calculator

Display Specs

Related Calculators

How to Use This Calculator

Enter your resolution

Enter the diagonal size

Read the PPI, dot pitch, and pixel count

Check retina status at your viewing distance

Formula & Methodology

Key Terms Explained

Real-World Examples

PPI in One Step

Resolution alone doesn't tell you sharpness

What 'retina' really means

Dot pitch and megapixels — the physical picture

Frequently Asked Questions

Get a branded PDF of your results

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