PPI (“pixels per inch”, in the acronym in English, or “pixels per inch”) is a measure that indicates the pixel density of a screen. The concept traces a relationship between resolution and display size. In general, the higher the pixel density of the screen, the better is the sharpness of the image.
Pixel density and image sharpness
A pixel is a point that represents the smallest unit of a digital image. Screens are made up of thousands or millions of pixels arranged in rows and columns.
Pixels are not the same size on all screens. That’s why there’s the measure of pixel density, abbreviated PPI. It indicates how many pixels the display concentrates in an inch.
The higher the PPI, the sharper the displayed image. That’s because more pixels are concentrated in an inch of screen. A screen with low density uses fewer pixels with larger size to fill the space, which leads to squared or pixelated images.
What is the ideal pixel density?
Pixel density is calculated based on resolution and screen size.
A 6-inch display with 720p has a much higher pixel density than a 32-inch TV with the same resolution. However, if the TV is viewed from a reasonable distance, its pixels are not easily identified.
Each type of device has a focal length that determines its ideal pixel density, which does not detract from image quality or user experience:
- Cell phones: the indication is that the display has at least 300 ppi, considering that we use the screens close to the face (about 30 cm);
- Monitors: it is recommended that the screen has between 80 and 150 ppi, considering that we use the monitor at distances between 50 and 100 cm from the face;
- TVs: ideally, the device should have at least something between 50 and 100 ppi. That’s because, in general, we use TVs at distances greater than 1 meter from the face.
It is common for the manufacturer to inform the PPI on the device’s website, especially when the number is high. But, after a certain limit, having a higher pixel density does not bring gains to image quality. On a hypothetical 6-inch phone, you’re unlikely to notice the difference between 400 and 500 ppi.
Other factors that affect image quality
Pixel density is not the only characteristic that determines the image quality of a screen. Among other factors are:
- panel type: OLED screens stand out for their color intensity and contrast. If you prefer an LCD display, models based on MiniLED have more satisfying levels of color reproduction than those with an LED backlight;
- Shine: High brightness levels are especially important for devices that are used outdoors, such as cell phones. In them, brightness above 600 nits ensure good viewing of the screen on sunny days (the more, the better);
- Viewing angle: the higher this parameter, the better the view of the screen from lateral positions;
- Update rate: indicates how many times the screen refreshes per second. Common screens normally work with 60 Hz (60 updates per second). For games, the ideal is a rate equal to or greater than 90 Hz;
- Resolution: parameter directly related to pixel density. The larger the screen, the higher the resolution should be. This is the case with TVs, where 4K resolution is recommended for models measuring 40 inches or more.
Common questions
The calculation is made with the application of the Pythagorean Theorem for the discovery of the diagonal resolution of the screen. Then that number is divided by the size of the display. To facilitate this task, you can search the web for PPI calculators online or in app form.
While PPI stands for “pixels per inch”, DPI stands for “dots per inch”. It is not uncommon for both measures to be treated as synonyms. However, the DPI was created to measure the density of prints on paper, and the PPI points out measurements specifically for digital images.
