PPI Calculator (Pixels Per Inch)
Work out the pixel density of any display from its resolution and screen size, or the DPI you need to print an image sharply — with dot pitch, physical dimensions and a live density scale.
Enter a screen's pixel resolution and its diagonal size to get the pixel density (PPI), dot pitch, physical dimensions and how sharp it is.
About the PPI / DPI Calculator
Pixel density is what makes one screen look razor-sharp and another look grainy, even at the same resolution. It is measured in PPI (pixels per inch): the number of pixels packed into each inch of the display. This calculator finds the PPI of any screen from just two things — its pixel resolution and its diagonal size — and also handles the print side, where the same idea is called DPI (dots per inch). Because pixels are laid out in a grid, the diagonal pixel count is found with the Pythagorean theorem, √(width² + height²), and dividing that by the diagonal size in inches gives the PPI. From the PPI you also get the dot pitch (the spacing between pixels in millimetres), the physical width and height of the panel, the total resolution in megapixels, and a plain-language density category from standard desktop displays up to Retina laptops and ultra-dense phone screens. On the print side it converts freely between an image's pixel dimensions and its printed size, so you can check whether a photo has enough pixels to print sharply — the rule of thumb being 300 DPI for photo-quality prints, around 150 DPI for drafts or large formats viewed from a distance, and 72 DPI for screen-only use. It is built for designers, developers, photographers and anyone choosing a monitor, laptop or phone and wondering how sharp it will really look.
How to use this calculator
- 1 Choose Screen PPI to measure a display's pixel density, or Print DPI to work with printed images.
- 2 For a screen, pick a device preset or type the horizontal and vertical pixels and the diagonal size (in inches, centimetres or millimetres).
- 3 Read the PPI, dot pitch, physical dimensions, megapixels and the density category, and see where the value sits on the density scale.
- 4 For print, pick Size from DPI to get the print dimensions at a chosen DPI, or DPI from size to find the resolution you need for a target print size.
How pixel density (PPI) and DPI are calculated
Pixel density is the number of pixels per inch of screen. Because the pixels form a rectangular grid, the total number of pixels along the diagonal comes from the Pythagorean theorem applied to the horizontal and vertical pixel counts. Diagonal pixels: diagonalPx = √(width² + height²) Pixel density: PPI = √(width² + height²) / diagonal(inches) For example, a 24-inch 1920×1080 monitor has √(1920² + 1080²) = 2202.9 diagonal pixels, so PPI = 2202.9 / 24 ≈ 91.8. A 6.1-inch phone at 2556×1179 works out to about 461 PPI — roughly five times denser, which is why phone text looks so crisp. Dot pitch: dot pitch (mm) = 25.4 / PPI This is the centre-to-centre distance between neighbouring pixels; smaller is sharper. PPI vs DPI: The two terms describe the same thing — dots or pixels per inch — but PPI is used for screens and DPI for print. For printing, the print size and DPI are linked directly: print size (inches) = image pixels / DPI required DPI = image pixels / print size (inches) So a 3000-pixel-wide image prints 10 inches wide at 300 DPI, and printing that same image 20 inches wide would drop it to 150 DPI.
Frequently asked questions
What is PPI (pixels per inch)?
PPI stands for pixels per inch — the number of pixels packed into each inch of a screen, a measure of how sharp the display looks. A higher PPI means smaller, denser pixels and crisper text and images. Typical desktop monitors sit around 80–110 PPI, high-resolution laptops reach 200–300 PPI (Apple calls this class Retina), and modern phones exceed 400 PPI. Two screens can share the same resolution yet have very different PPI, because a smaller screen squeezes the same pixels into less space.
How do I calculate PPI or pixel density?
Take the horizontal and vertical pixel counts, combine them into the diagonal pixel count with the Pythagorean theorem √(width² + height²), then divide by the screen's diagonal size in inches: PPI = √(width² + height²) / diagonal. For example, a 27-inch 4K (3840×2160) monitor gives √(3840² + 2160²) / 27 = 4405.8 / 27 ≈ 163 PPI. This calculator does the arithmetic for you and also reports the dot pitch, physical size and density category.
What is the difference between PPI and DPI?
PPI (pixels per inch) and DPI (dots per inch) both describe how many dots fit in one inch, but they apply to different media. PPI refers to the pixels of a digital display or a source image, while DPI refers to the ink dots a printer lays down on paper. In everyday use the terms are often swapped, and the maths is the same: for printing, print size = image pixels / DPI. The practical point is that a screen image at a given pixel size can be printed large (low DPI, softer) or small (high DPI, sharper).
What DPI should I print at?
For photo-quality prints viewed up close, aim for 300 DPI — this is the standard for photo labs and magazines. Around 150 DPI is fine for drafts, posters and large prints that are viewed from a distance, and 72 DPI is only suitable for on-screen use. To hit 300 DPI you need enough pixels: multiply the print size in inches by 300 to find the minimum pixel dimension, so a sharp 10×8 inch photo print needs at least 3000×2400 pixels. Use the DPI from size mode to check whether your image has the resolution you need.
Related design & screen tools
PPI pairs naturally with the aspect ratio calculator for working out screen and image proportions, the CSS unit converter for translating pixels into rem, em and other web units, the paper size reference for choosing print formats, and the color converter for the rest of your design workflow.