DPI vs PPI: the difference, and why 300 dpi matters

The short answer to dpi vs ppi: PPI (pixels per inch) describes a digital image or a screen, and DPI (dots per inch) describes how finely a printer lays down ink. In everyday use they are treated as the same thing, and when a print shop asks for "300 dpi" they really mean 300 pixels per inch at the finished size. What matters is the pixel count: multiply the print size in inches by 300 and you have the pixels you need.

What PPI and DPI actually measure

A printer needs several ink dots to reproduce the colour of one pixel, which is why printers quote dot densities far higher than 300. So the two numbers describe different things. Because design software and print shops say "dpi" for both, it is safest to translate any request for "300 dpi" into "300 pixels for every inch of the printed piece".

The one sum you need

pixels      = inches x ppi
print size  = pixels / ppi

6 x 4 in postcard at 300 ppi  ->  1800 x 1200 px
A4 (8.27 x 11.69 in) at 300   ->  2480 x 3508 px
1080 x 1350 px at 300 ppi     ->  3.6 x 4.5 in

millimetres to inches: divide by 25.4

Run the sum backwards and you learn how large an existing image can print. A 1080 × 1350 Instagram post at 300 ppi prints sharply at only 3.6 × 4.5 inches. Stretch it to A4 and each pixel is stretched to more than twice its width, which is when prints look soft. Our guide to resolution for printing has a full table of sizes.

Why 300 dpi for print and 72 dpi is a myth

300 pixels per inch is the long standing print standard because, at normal reading distance, people can't make out individual pixels beyond roughly that density. Posters and banners seen from further away can use less, often 150, which is covered in poster sizes.

The idea that web images should be "72 dpi" comes from early Mac screens, which happened to show 72 pixels per inch. Screens ignore the dpi label entirely; a browser or phone shows an image by its pixel dimensions. A 1200 × 630 image labelled 72 dpi and the same image labelled 300 dpi look identical on screen and are exactly the same file size, give or take a few bytes of metadata.

Resolution is not the only thing that changes between a screen and paper. Colour shifts too, because screens mix light and presses mix ink; RGB vs CMYK explains what to expect, and printing gradients covers the smooth blends that suffer most.

Changing dpi does not add detail

Most image editors let you type a new dpi value. If you change the number without resampling, the pixels stay the same and only the suggested print size changes. If you resample upwards, the software invents new pixels by blending neighbours, which makes the image bigger but not sharper. The only real fix for a low resolution image is a larger original or a design that can be rendered again at the size you need.

Pixel density on screens

Screens have a real ppi: modern phones pack far more pixels into an inch than an old desktop monitor. To keep things readable, they draw each CSS pixel with two or three physical pixels. That is why a sharp web image is usually exported at twice the size it is displayed. The browser picks the right one if you offer it:

<img
  src="hero-1200.png"
  srcset="hero-1200.png 1x, hero-2400.png 2x"
  width="1200" height="600"
  alt="Spring collection hero"
/>

Gradients and rendered designs dodge most of this. Because they have no fixed pixels, they can be drawn again at whatever size a screen or printer needs. Gradiently's print sizes are set at 300 dpi already, custom sizes go up to 8,000 pixels, and Pro exports up to 4K as well as SVG and print PDF. For choosing formats, see PNG vs JPG and SVG vs PNG.