Understanding PPI (Pixels Per Inch)
PPI stands for Pixels Per Inch. It is a measurement of the pixel density of an electronic image device, such as a computer monitor or television screen. It indicates how many individual pixels are packed into a one-inch line of the display.
The Calculation
To find the PPI, we first calculate the diagonal resolution in pixels using the Pythagorean theorem:
- Step 1: Calculate diagonal pixels: $\sqrt{Width^2 + Height^2}$.
- Step 2: Divide diagonal pixels by the diagonal physical size (in inches).
Formula: $PPI = \frac{Diagonal_{pixels}}{Diagonal_{inches}}$
Inches vs Centimeters
The diagonal size of a screen can be measured in either inches or centimeters. Since the mathematical definition of PPI uses inches, if your measurement is in centimeters, it must be converted first:
$$ \text{Inches} = \frac{\text{Centimeters}}{2.54} $$
PPI Classifications
Different PPI values offer different viewing experiences:
- ~72-96 PPI (Low Density): Standard for older monitors. Large, visible pixels.
- ~110-160 PPI (Standard): Typical for desktop monitors and laptops. Sharp enough for most users at viewing distance.
- ~220-300 PPI (Retina/High Density): Apple's "Retina" standard. Pixels are not visible to the naked eye at normal viewing distance. Creates very crisp text.
- 400+ PPI (Ultra High): VR Headsets (e.g., Apple Vision Pro) or modern high-end smartphones.
Frequently Asked Questions (FAQ)
What is Pixel Pitch?
Pixel Pitch is the distance between the centers of two physical pixels on the display. It is usually measured in millimeters (mm). Lower pitch means higher density. It can be calculated as $\frac{25.4}{PPI}$.
Does higher PPI mean more battery usage?
Yes. Higher PPI screens require more backlight and processing power to drive the additional millions of pixels. However, with modern OLED and efficient backlights, this difference is becoming negligible.
What is the standard print PPI?
Printers typically have much higher PPI than screens to ensure ink dots are not visible. Standard "photo quality" prints are around 300 PPI, while professional printing can exceed 600 PPI.
Common Resolutions (16:9 Aspect Ratio)
- 1080p (FHD): 1920 × 1080. ~2.1 MP.
- 1440p (QHD): 2560 × 1440. ~3.7 MP.
- 4K (UHD): 3840 × 2160. ~8.3 MP. Requires a 24-inch monitor to be >180 PPI.