PPI / DPI Calculator
Pixels per inch (PPI) is a measure of pixel density that describes how many individual pixels fit within one inch of a display. A higher PPI means more detail is packed into the same physical area, resulting in sharper, crisper images. This calculator computes PPI from a screen's resolution (width and height in pixels) and its physical diagonal size in inches using the formula PPI = √(width² + height²) / diagonal.
Beyond PPI, this tool also calculates dot pitch — the physical distance between the centers of adjacent pixels in millimeters — and the total resolution in megapixels. These metrics are essential when comparing monitors, choosing a phone or tablet, evaluating camera sensors, or printing at the correct resolution. A display with PPI above 200 is generally considered high-DPI or Retina-class, where individual pixels become imperceptible to the naked eye at normal viewing distances.
How it works
PPI = √(horizontal_pixels² + vertical_pixels²) / diagonal_inches. Dot pitch (mm) = 25.4 / PPI. Megapixels = (horizontal_pixels × vertical_pixels) / 1,000,000.
Use cases
- Comparing the sharpness of monitors, TVs, and mobile displays
- Determining whether a screen qualifies as Retina or high-DPI
- Calculating print resolution requirements for photos and graphics
- Evaluating camera sensor pixel density and image clarity
- Choosing the right display for graphic design, video editing, or gaming
Frequently asked questions
What is the difference between PPI and DPI?
PPI (pixels per inch) measures pixel density on a digital display, while DPI (dots per inch) measures ink dots when printing. The terms are often used interchangeably in casual use, but PPI is the correct term for screens and DPI for printers. This calculator computes PPI for displays.
How do you calculate the PPI of a screen?
Use PPI = √(horizontal_pixels² + vertical_pixels²) / diagonal_inches. First find the diagonal resolution with the Pythagorean theorem, then divide by the physical diagonal size. For example, a 1920×1080 screen at 24 inches has a diagonal of about 2203 pixels, giving roughly 92 PPI.
What PPI counts as a Retina or high-DPI display?
A display is generally considered high-DPI or Retina-class when its PPI is high enough that individual pixels are indistinguishable at a normal viewing distance — typically above 200 PPI for phones and around 220 PPI for laptops. The exact threshold depends on viewing distance, since farther screens can have lower PPI and still look sharp.
What is dot pitch and how is it related to PPI?
Dot pitch is the physical distance between the centers of adjacent pixels, usually in millimeters. It is the inverse of pixel density: dot pitch (mm) = 25.4 / PPI. A smaller dot pitch means pixels are closer together and the image is sharper, so a 300 PPI screen has a dot pitch of about 0.085 mm.
Does a higher resolution always mean a sharper screen?
Not by itself — sharpness depends on pixel density (PPI), which combines resolution and physical size. A 4K resolution looks extremely sharp on a 27-inch monitor but less dense on a 65-inch TV, because the same pixels are spread over a larger area. That is why comparing PPI is more meaningful than comparing resolution alone.