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Understanding Pixel Density (PPI)
Pixel Density, measured in PPI (Pixels Per Inch), determines how sharp and clear images appear on a screen. It's calculated by dividing the diagonal pixel resolution by the physical screen size in inches.
Higher PPI means more pixels are packed into each inch, resulting in sharper text, clearer images, and a better overall viewing experience. This is why modern smartphones with 400+ PPI look incredibly crisp compared to older monitors with 90 PPI.
💡 Expert Tip: The "Retina" Threshold
Apple popularized the term "Retina Display" for screens where individual pixels are imperceptible at typical viewing distances. For phones (held ~10-12 inches away), this is ~300-326 PPI. For laptops (~20 inches), it's ~220 PPI. For desktop monitors (~24 inches), it's ~110 PPI. Closer viewing = higher PPI needed.
⚠️ Common Mistake: Confusing PPI with DPI
Many people use PPI and DPI interchangeably, but they're different. PPI is for screens (pixels per inch on a display). DPI is for printers (dots of ink per inch on paper). When talking about monitors, phones, or TVs, always use PPI.
Formula Explained
The PPI formula uses the Pythagorean theorem to find the diagonal pixel resolution:
PPI = √(width² + height²) / diagonal_inches
Example: A 27-inch monitor with 2560×1440 resolution:
- Diagonal pixels = √(2560² + 1440²) = √(6,553,600 + 2,073,600) = √8,627,200 ≈ 2,937 pixels
- PPI = 2,937 / 27 ≈ 109 PPI
PPI Benchmarks
- 80-100 PPI: Standard desktop monitors (acceptable, but pixels may be visible)
- 110-140 PPI: High-quality desktop displays (crisp text, good for productivity)
- 220+ PPI: Retina-class laptops (MacBook Pro, Dell XPS)
- 300-500+ PPI: Smartphones (iPhone, Samsung Galaxy)
Reviewed by: Marcus Lee, Display Technology
Specialist
Last updated: November 27, 2025
Frequently Asked Questions
What is PPI?
PPI stands for Pixels Per Inch. It's a measurement of pixel density that indicates how many pixels are packed into one inch of a screen. Higher PPI means sharper, more detailed images.
What's the difference between PPI and DPI?
PPI (Pixels Per Inch) refers to screen displays and digital images, while DPI (Dots Per Inch) refers to printed output. For screens, always use PPI. DPI is for printers.
What is a good PPI for a monitor?
For desktop monitors, 90-110 PPI is standard. For high-quality displays, aim for 140-160 PPI. Smartphones typically range from 300-500+ PPI.
How do I calculate PPI?
Use the formula: PPI = √(width² + height²) / diagonal_inches. First calculate the diagonal pixel resolution using the Pythagorean theorem, then divide by the screen size in inches.