How is PPI calculated?

PPI (Pixels Per Inch) is calculated using three steps: (1) Find the diagonal pixel count using the Pythagorean theorem: √(width² + height²). (2) Divide by the screen's physical diagonal size in inches. For example, a 1920×1080 display on a 24" screen: √(1920² + 1080²) ÷ 24 ≈ 91.8 PPI.

What is a good PPI for a phone?

Modern smartphones typically range from 300–500 PPI. Apple's original Retina display standard for phones (held at ~10–12") was 326 PPI. Most flagship phones today exceed this: iPhone 16 Pro is 460 PPI, Samsung Galaxy S24 Ultra is ~500 PPI. At normal phone-viewing distance, anything above 300 PPI will appear sharp to the human eye.

What is a good PPI for a monitor?

For a monitor viewed from about 24", the retina threshold is approximately 143 PPI. A standard 27" 1080p monitor has ~82 PPI (below retina), a 27" 1440p has ~109 PPI (still below), and a 27" 4K has ~163 PPI (above retina). For a truly sharp desktop experience, a 4K monitor or a 5K Apple Studio Display (218 PPI) is ideal.

What does 'Retina display' mean?

Apple coined 'Retina display' to describe a screen where individual pixels are not distinguishable at a typical viewing distance. The threshold is based on the human eye's angular resolution of ~1 arc-minute. Apple's original iPhone Retina display was 326 PPI (held at ~10"). The concept applies to any display: a screen is 'retina-quality' when its PPI exceeds 3438 ÷ viewing_distance_in_inches.

What is the difference between PPI and DPI?

PPI (Pixels Per Inch) refers to screen pixel density. DPI (Dots Per Inch) refers to printer ink dot density. They measure fundamentally different things. On screens, PPI is the correct term. On printers, DPI is correct. The confusion arises because both describe 'density per inch' — but pixels are light-emitting elements, while dots are ink deposits. For web design, 72–96 PPI is standard. For print-quality artwork, 300 PPI is recommended.

Does higher PPI always mean a better display?

Not necessarily. Beyond the retina threshold for your viewing distance, additional PPI provides no perceptible benefit. Other factors like panel technology (IPS vs OLED vs TN), color accuracy, brightness, refresh rate, and contrast ratio matter significantly. A 400 PPI AMOLED panel may look far better than a 600 PPI LCD with poor color calibration.

What is dot pitch and why does it matter?

Dot pitch (also called pixel pitch) is the physical size of one pixel, measured in millimeters. It equals 25.4mm ÷ PPI. A lower dot pitch means smaller, denser pixels — which gives a sharper image. A 27" 4K monitor has a dot pitch of ~0.155mm, while a 55" 4K TV has ~0.317mm. Dot pitch is particularly important for LED walls and professional monitors where viewing distance varies.

How many megapixels is my screen?

Megapixels = (width × height) ÷ 1,000,000. A 1920×1080 display is 1920 × 1080 = 2,073,600 pixels = ~2.07 megapixels. A 4K (3840×2160) display is ~8.3 megapixels. A 5K (5120×2880) display is ~14.7 megapixels. For comparison, a modern smartphone camera sensor is 48–200 megapixels — far exceeding any current display.

What PPI do I need for printing?

For photographic print quality, the recommended image resolution is 300 PPI at the final print size. This means a 4×6" print needs an image of 1200×1800 pixels. For large-format printing (banners, posters) viewed from a distance, 150 PPI is often sufficient. Note: this is different from monitor PPI — here PPI refers to the image's resolution density when printed.

Why does my 4K TV look less sharp than my phone?

Because PPI is relative to screen size, not just resolution. A 65" 4K TV has ~67 PPI. A phone with 1080p at 6.1" has ~400 PPI. Despite both using similar resolution tiers, the TV's pixels are physically much larger. However, at a typical TV viewing distance of 8–10 feet, 67 PPI is well above the retina threshold (~38 PPI at 90"). So the TV appears sharp in normal use — just not up close.

PPI Calculator

Device Type

Device

Viewing Distance

Used to determine if this display is "retina" quality at your typical viewing distance.

Typical: Phone 12", Monitor 24", TV 120"

Pixels Per Inch

108.8PPI

Pitch0.233mm

MP3.69

Res2560×1440

Sharpness at Viewing Distance

Retina threshold at your specified viewing distance

Adequate

Below retina — needs 143 PPI, has 109 PPI

0 PPIRetina (143 PPI)287 PPI

Your display: 109 PPI✗ Not Retina

Low

Marginal

Adequate

Sharp

Very Sharp

Physical Dimensions

Actual physical size of the display

Width

597.7mm

23.53"

Height

336.2mm

13.24"

Diagonal

685.8mm

27.00"

Pixel Size

233µm

0.233mm/px

PPI Comparison

How your display compares to common screens

55" 4K TV80 PPI

Standard 1080p 24" Monitor92 PPI

QHD 1440p 27" Monitor109 PPI

▸ Your Display109 PPI

4K 27" Monitor163 PPI

5K 27" Monitor218 PPI

Apple iPad Pro 11"264 PPI

Apple iPhone SE326 PPI

Apple iPhone 16 Pro460 PPI

Samsung Galaxy S24 Ultra505 PPI

How PPI is Calculated

PPI measures how many pixels fit into one linear inch. Here's the math.

Formula

diagonal_px = √(width² + height²)

PPI = diagonal_px ÷ screen_size_inches

dot_pitch = 25.4mm ÷ PPI

retina_threshold = 3438 ÷ viewing_distance_inches

Step 1: Find the diagonal resolution

Use the Pythagorean theorem: diagonal_px = √(width² + height²). For a 1920×1080 display: √(1920² + 1080²) = √4,852,800 ≈ 2,202.9 pixels.

Step 2: Divide by physical screen size

Divide the diagonal pixel count by the screen's diagonal size in inches. PPI = diagonal_px ÷ screen_size_inches. A 24" 1080p monitor: 2,202.9 ÷ 24 = 91.8 PPI.

Step 3: Calculate dot pitch

Dot pitch (physical pixel size) = 25.4mm ÷ PPI. At 92 PPI, each pixel is 25.4 ÷ 92 = 0.276mm wide. Smaller dot pitch = finer, sharper detail.

Step 4: Assess retina quality

The retina threshold uses the 1 arc-minute rule. At 24" distance: 3438 ÷ 24 = 143 PPI minimum for retina sharpness. Anything above this threshold is indistinguishable to the naked eye.

What is a Good PPI?

“Good” PPI depends entirely on how close you sit to the screen.

Device Type	Typical PPI	Viewing Distance	Retina Threshold
Smartphone	300–500 PPI	10–12"	~287 PPI
Tablet	220–330 PPI	14–18"	~191–246 PPI
Laptop	160–250 PPI	18–22"	~156–191 PPI
Desktop Monitor	90–220 PPI	24–30"	~115–143 PPI
TV	40–100 PPI	5–10 ft	~29–57 PPI

Common Mistakes

Avoid these misunderstandings when evaluating display sharpness.

Confusing PPI with DPI

PPI (Pixels Per Inch) measures screen density. DPI (Dots Per Inch) is a print term for ink density. A screen has PPI; a printer has DPI. Many people incorrectly say "DPI" when they mean screen pixel density.

Ignoring viewing distance

A 100 PPI monitor looks fine at 3 feet but pixelated at 12 inches. PPI only matters relative to how far you sit from the screen. A 4K TV has ~80 PPI — perfectly sharp at 10 feet, not up close.

Assuming more pixels = sharper

Increasing resolution without changing screen size raises PPI. But if you scale the UI (e.g. 200% HiDPI / Retina mode), the effective rendered density may be unchanged. What matters is rendered pixel density at your viewing distance.

Misidentifying screen size

Screen size is always measured diagonally corner to corner of the active display — not including bezels. A monitor advertised as 27" may have a 26.5" actual panel. Use the true active diagonal for an accurate PPI calculation.

PPI vs DPI — What's the Difference?

These two terms are often used interchangeably, but they refer to different technologies.

Property	PPI	DPI
Stands for	Pixels Per Inch	Dots Per Inch
Used for	Digital screens & displays	Printers & print media
What it measures	Screen pixel density	Ink dot density on paper
Calculation	Resolution + screen size	Printer hardware spec
Typical range	72–500+ PPI	72–2400+ DPI

When designing for both screen and print: use PPI for screen assets (72–96 PPI for web, 300 PPI for print-quality) and DPI for printer settings. An image at 300 PPI will print at ~300 DPI, giving photographic quality output.

Frequently Asked Questions

Common questions about pixel density, PPI, and display sharpness