What Is Pixels Per Inch (PPI)?

Pixels per inch (PPI) is the measure of resolution in a digital image or video display. A pixel is an area of illumination or color on a screen or computer image.

PPI measures the display resolution, or pixel density, of a computer monitor or screen. The measure is also used to indicate the resolution of a digital image, as well as the resolution capacity of a camera or scanner capturing an image.

Key Takeaways

  • Pixels per inch (PPI) is the measure of resolution in a digital image or video display.
  • Pixels per inch (PPI) is typically used to refer to the display resolution, or pixel density, of a computer monitor or screen.
  • The greater the pixels per inch (PPI), the greater the detail in the image or display.
  • In the early 2000s, the most common computer display resolution was 1024 x 768; by 2019, 1920 x 1080 was common.

Understanding Pixels Per Inch (PPI)

A monitor or screen with a high number of PPI will show a greater level of detail. Similarly, a digital image containing a large number of pixels will hold more detailed visual information and, therefore, it will be able to be reproduced in larger formats without pixelation (a form of image distortion in which individual pixels become visible to the naked eye).

A pixel is a single point of data in a digital image or in a monitor, and the PPI measurement indicates the number of pixels contained within the image or screen. Pixels per inch is expressed by indicating the number of pixels available horizontally by the number available vertically. Thus, an image that is 200 pixels across and 200 pixels down will be expressed as a 200 x 200 PPI image. Although there are exceptions, most devices rely on square pixels in capturing and displaying images.

Digital cameras will frequently express resolution in terms of megapixels. The megapixel measurement is determined by multiplying the horizontal PPI measure by the vertical PPI measure. For instance, a camera that captures images at 1600 x 1200 is considered a 1.92-megapixel camera.

The PPI of a captured image helps to determine the maximum size an image can be printed without pixelation. For example, a 1.92-megapixel camera is capable of producing good quality 4 x 6-inch prints, but prints larger than that size will begin to look blurry or fuzzy.

Industry standards for PPI in computer monitors, televisions, scanners, and cameras have improved rapidly in recent years. In the early 2000s, for instance, the most common computer display resolution was 1024 x 768. By 2012 the industry standard had increased to 1366 x 768. In the year 2019, 1920 x 1080 was common.

Pixels Per Inch (PPI) vs. Dots Per Inch (DPI)

Although PPI is used interchangeably with dots per inch (DPI) to discuss image resolution, the two terms have important differences.

PPI tends to refer to an input resolution, which is the measure by which a camera or scanner captures an image (or by which an image is created or manipulated on a monitor).

DPI, on the other hand, refers to an output resolution. For many years, for instance, early web pages recommended saving images at no greater resolution than 72 DPI for websites, as this measurement typically displayed sufficient visual information on websites while minimizing site load times. In the days of dial-up internet access, this practice was especially common.

For print, on the other hand, typical recommendations indicate that images should be at least 300 DPI for high-resolution print quality. For designers, artists, and others concerned with high print quality, however, output images may require much larger resolutions than 300 DPI.