Resolution and DPI for printing: the practical guide

Table of contents

1. What resolution a print file needs
2. DPI and PPI: what they really mean
3. Why 300 ppi is the standard
4. Effective resolution: the number that really matters
5. How to tell if an image will print pixelated

What resolution does a print file need?

A print file needs its images at 300 ppi (pixels per inch) at the final print size. That is the point beyond which the eye stops telling individual pixels apart on paper, at a normal reading distance. Below 150 ppi the image looks clearly pixelated or blurred, no matter how perfect it seems on screen.

Resolution is not a whim of the print shop: it is the amount of information the machine has to reproduce every millimetre of the design. If that information is not in the file, no machine can invent it.

DPI and PPI: what they really mean

Day to day they are used as synonyms, and for getting the point across that is fine. But it is worth knowing the difference, because it explains several common misunderstandings.

• PPI (pixels per inch): describes the digital image. It is how many pixels there are in each inch of image. It is what you control when you design.
• DPI (dots per inch): describes the machine. It is how many ink dots the output device lays down per inch. The print shop controls it.

When a client asks for a file "at 300 dpi", they almost always mean 300 ppi of image. The distinction matters because a machine can print at 2,400 dpi and still reproduce a poor image if the file arrives at 100 ppi: the ink dots are plenty, the image pixels are missing.

Why is 300 ppi the standard?

Because it is the balance between visible quality and a manageable file size for commercial work seen up close. Going above 300 ppi rarely adds perceptible sharpness and inflates the file weight; going below starts to show quickly.

The right number depends on viewing distance:

The logic is simple: the farther away something is viewed, the less resolution it needs, because the eye cannot tell the detail apart either. A billboard at 300 ppi would be a huge, pointless file. A flyer at 100 ppi, on the other hand, is printed rubbish.

Effective resolution: the number that really matters

Effective resolution is the real resolution of an image at the size it is placed in the design, and it is the only thing that counts. An image can be 300 ppi in its original file and end up at 150 effective ppi if you scale it to double in the layout.

This is the mistake that most often turns a job pixelated without anyone noticing: a "300 ppi" photo is taken, stretched to fill a large space, and its effective resolution collapses. That is why enlarging a small image fixes nothing. Raising the ppi value in the software does not either: it adds no detail, it only interpolates, that is, it invents pixels from the ones already there. The result looks soft.

The only reliable solution is to start from originals with pixels to spare for the final size. Resolution is always checked at the placement size, not on the loose file. It is part of what we cover in the guide to preparing a PDF for print.

How do you tell if an image will print pixelated?

By eye, reviewing image by image in prepress, you can. But it is slow and comes late: by the time someone spots the 90 ppi photo, the job is already in the queue. The alternative is to check the effective resolution of every image automatically, the moment the file arrives.

It is one of the validations Entregarte runs when the client uploads the PDF: it checks the resolution of every embedded image at the size it appears and warns when it falls below the threshold the print shop defines, showing the exact value found. That way a pixelated image is caught and explained before it reaches the machine, not after.

In 2026, the low-resolution file is still one of the most common and most avoidable reasons for a reprint. Checking it at upload closes that door without anyone having to open every image by hand. If you want to see how, take a look at the validations and try it free for 7 days, no card required.