DPI vs PPI: What's the Difference?

This guide follows a single image, 3000 × 2400 pixels, through several print sizes. Seeing the same pixels spread over different areas of paper is the quickest way to understand which number matters, and when.

What is PPI?

A digital image is a grid of pixels with fixed dimensions. A 3000 × 2400 px photo contains exactly 3000 pixels across and 2400 down, whatever you do with it. On its own, that grid has no physical size.

PPI gives it one. Pixels per inch says how many of those pixels sit in one linear inch once the image is printed or displayed at a particular size. Print the 3000-pixel width across 10 inches and you get 300 PPI. Spread it across 20 inches and you get 150 PPI. The pixels haven't changed; they have simply been stretched over more paper.

What is DPI?

Dots per inch is a property of an output device. A printer builds the picture from tiny dots of ink or toner, and its DPI rating describes how closely it can place them. A printer doesn't have one fixed figure: the DPI it uses can depend on the print mode and driver settings you pick.

Printer dots and image pixels are not the same thing. Most printers can't lay down every colour directly; they reproduce colours and tones with patterns of small dots (halftoning or dithering), so a single image pixel is often built from several printer dots. Methods vary between printers, and there is no fixed number of dots per pixel. This is why a printer's DPI rating is typically much higher than the PPI of the image you send it. You don't need to match the two numbers; you only need enough image pixels for the size you are printing.

DPI vs PPI: key differences

Why the terms get mixed up

In everyday printing, people, print services and many editing apps say "DPI" when they mean the image's PPI. If a print shop asks for a 300 DPI file, it wants the image to have about 300 pixels per inch at the size it will be printed. In that context the two terms are being used for the same thing, even though, strictly, they measure different things.

One image, four print sizes

Here is the same 3000 × 2400 px image at four different PPI values. The pixel dimensions stay the same in every row.

These results assume the original pixel dimensions are unchanged. As PPI falls, each pixel covers more paper. Whether that looks soft depends on the image and on how closely people will look at the print.

What happens when you change DPI in an image editor?

Most editors have a "resolution" or "DPI" box. What happens when you change it depends on whether resampling is switched on.

Without resampling

The pixels stay exactly the same. Only a note stored in the file changes, which tells software what size to print the image by default. Changing our example from 72 to 300 changes the default print size from 41.67 × 33.33 in to 10 × 8 in, but the image contains the same 3000 × 2400 pixels and the same detail.

With resampling

The editor adds or removes pixels to reach the new size. Scaling up creates new pixels by estimating them from the existing ones, so the file gets larger, but it can't restore detail that was never captured. Scaling down discards pixels.

Is 300 DPI always necessary?

300 PPI is a common target for high-quality prints that people look at up close, such as photos, books and flyers. It is not a universal requirement. Large prints like posters and banners are usually viewed from further away, so lower PPI values are often acceptable for them.

DPI vs PPI for screens

Screens have a pixel density too, usually quoted as PPI: the display's pixel count divided by its physical size. It describes the screen, not the image, and it has no effect on how an image file prints. On screen, an image's pixel dimensions are what matter. The resolution value stored in the file can set an image's default print size, but changing it without resampling doesn't change the pixel dimensions. Work out any display's density with the PPI Calculator.

The "72 PPI" often linked to web images is a historical convention, not a maximum. A digital image can have any number of pixels.

How to calculate print dimensions

Working backwards: an 8 × 10 in print at 300 PPI needs 2400 × 3000 pixels, and a 4 × 6 in print needs 1200 × 1800 pixels. To convert one dimension, use Pixels to Inches. To find the PPI your image will have at a size you already know, use the DPI Calculator.

Common misconceptions

• "Raising the DPI number makes my image sharper." Without resampling it changes only the default print size; with resampling it adds estimated pixels, not new detail.
• "72 PPI images can't be printed." The number stored in the file doesn't decide that. Print size and pixel count do.
• "Every print needs 300 DPI." It's a common target for close viewing, not a rule for every print.
• "A 1200 DPI printer needs a 1200 PPI image." Printer dots and image pixels are different units; printers use several dots to reproduce a pixel.
• "An image has a fixed DPI." An image has pixel dimensions. Its effective PPI depends on the size you print it.