DPI vs PPI: What’s the Difference?

PPI (pixels per inch) describes how densely pixels are packed in a digital image or on a screen, while DPI (dots per inch) describes how many ink dots a printer lays down. For the web, only pixel dimensions matter; for print, the pixels-per-inch you print at decides how sharp the result looks.

By Sumair Roudani · Published October 27, 2026

Two different things measured per inch

Both terms describe density, but of different things.

• PPI, pixels per inch, belongs to the digital world. A screen has a physical PPI (how many pixels fit in an inch of glass), and an image can be assigned a PPI that tells software how large to print it.
• DPI, dots per inch, belongs to printers. An inkjet or laser printer builds each pixel's color from many tiny dots of a few ink colors. A printer advertised at 1200 or 2400 DPI is describing its mechanism, not your image.

Put simply: pixels are what your file is made of, and dots are how a printer reproduces those pixels on paper. A single image pixel printed at 300 PPI on a 1200 DPI printer is rendered with a small grid of ink dots.

Why the terms get mixed up

In practice, almost everyone says "DPI" when they mean PPI. Print shops ask for "300 DPI files", camera and editing software often labels the image resolution field as DPI, and Windows calls display scaling "DPI scaling". The habit is so common that it isn't worth correcting people. Just know that when someone asks for a "300 DPI image", they want an image with enough pixels to print at 300 pixels per inch at the final size.

The only time the strict difference matters is when you're reading a printer spec sheet. A printer's DPI rating says nothing about what resolution your file should be.

What matters for screens

On a screen, an image is displayed using its pixel dimensions. A 1200 × 800 photo is 1200 × 800 pixels whatever DPI value is stored in its metadata.

The screen's own PPI decides how physically large and how sharp those pixels look. You can calculate it from the resolution and diagonal: PPI = √(width² + height²) ÷ diagonal in inches. The PPI calculator does this for any display.

Worked example: screen density

For the 24-inch monitor: √(1920² + 1080²) ≈ 2203 pixels along the diagonal, and 2203 ÷ 24 ≈ 92 PPI. The phone packs about five times as many pixels into each inch, which is why phones scale content up by a device pixel ratio of 2 or 3. That scaling is covered in our guide to sharp images on retina screens.

What "72 DPI for web" really means

You will still see advice to "save web images at 72 DPI". It has no effect on how an image appears on a website. Browsers lay out images using their pixel dimensions and the CSS you apply. The DPI value an image editor writes into the file doesn't change that in normal use (a few browsers can read special EXIF density tags, but the ordinary 72 or 300 setting isn't something to design around). Save the same 1200-pixel-wide JPEG at 72 DPI and at 300 DPI, and both display identically and have almost the same file size.

The number comes from history. Early Macintosh screens had roughly 72 pixels per inch, which matched the typographic point (1/72 of an inch), so one pixel on screen equaled one point in print. Windows later assumed 96 pixels per inch, and the CSS pixel is defined using that 96-per-inch reference. Modern screens range from under 100 to more than 450 PPI, so no single DPI value describes "the web".

What actually matters for web images:

• Pixel width and height, ideally around twice the displayed CSS size for high-density screens.
• Format and compression, which decide file size.
• The width and height attributes in your HTML, which prevent layout shift.

What matters for print

For print, the pixels per inch you print at controls sharpness. The maths is simple division.

print width (in)  = pixel width  ÷ PPI
print height (in) = pixel height ÷ PPI

pixels needed     = print size (in) × PPI

The DPI field in an image file is really a print-size instruction. A 3000 × 2000 pixel photo marked 300 PPI will open in layout software at 10 × 6.67 inches. Mark it 150 PPI and it opens at 20 × 13.33 inches. The pixels are identical; only the suggested physical size changes.

Worked example: can I print this photo at 8 × 10?

You have a 3000 × 2400 pixel image and want an 8 × 10 inch print at 300 PPI.

1. Pixels needed: 8 × 300 = 2400 by 10 × 300 = 3000.
2. Your image is 2400 × 3000 when rotated to portrait, an exact match.
3. Result: it prints at a full 300 PPI with no upscaling.

Now try a 16 × 20 inch poster from the same file: 3000 ÷ 20 = 150 PPI. That's half the usual photo target, but a poster is normally seen from further away, so it will often look fine. The DPI and print size calculator runs these numbers in both directions.

Typical PPI targets by use

These are common rules of thumb, not standards. Your printer or print shop may have its own requirements, so always check their spec sheet.

Resampling vs changing the DPI number

Image editors give you two ways to change resolution, and confusing them causes most DPI problems.

• Without resampling: the pixel count stays fixed. For a 3000-pixel-wide image, raising PPI from 72 to 300 just shrinks the print width from about 41.7 inches to 10 inches. Quality is untouched.
• With resampling: the software adds or removes pixels. Downsampling is safe. Upsampling invents pixels by interpolation, so a small image upscaled to 300 PPI gets bigger but not sharper. AI upscalers can do better, but they're guessing detail rather than recovering it.

If you need to work out new dimensions while keeping the proportions, the image resize calculator helps.

Quick reference

For the screen side of the story, the W3C's CSS Values specification explains how CSS pixels relate to physical inches on screen.