Metadata

Change the DPI of an Image

Set an image to 300 DPI for print, or any other value. Writes every field that matters, so the change actually shows up when the printer opens the file.

Your files never leave this device. Everything happens inside your browser, so there is no upload, no server copy and nothing to delete afterwards. You can test that claim: load this page, turn off your internet connection, and the tool still works.

DPI is a label, not a quality setting

This is the single most misunderstood number in digital imaging, and clearing it up makes everything else straightforward.

An image file contains a grid of pixels. That is all it contains. A photo that is 3000 by 2000 pixels has exactly the same information whether it is labelled 72 DPI or 300 DPI — changing the label does not add or remove a single pixel.

What DPI records is an instruction about physical size: how many of those pixels should be packed into each inch of paper. At 300 DPI, a 3000 pixel wide image prints 10 inches wide. At 150 DPI, the same file prints 20 inches wide — bigger, and correspondingly coarser, from identical data.

So when a printer asks for 300 DPI, they are really asking for two things: enough pixels for the size you want, and a label that tells their software how to place them. Only the first affects quality.

Why DPI changes made elsewhere often do nothing

This is the specific bug this tool exists to fix, and it has a precise cause.

A JPEG can record its resolution in two entirely separate places. One is the JFIF header, an old and simple structure near the start of the file with fields for horizontal and vertical density. The other is inside the EXIF block, as the tags XResolution, YResolution and ResolutionUnit.

Most online DPI tools write only the JFIF fields. Photoshop, InDesign and Word read the EXIF tags. So the tool reports success, the file genuinely changed, and when you open it in the program that matters it still says 72 DPI — because the EXIF value was never touched and is still sitting there.

This tool writes both, and forces the EXIF resolution unit to inches so the number cannot be reinterpreted as dots per centimetre. If the file has no JFIF header at all, one is inserted. The result reads consistently everywhere.

How many pixels do you actually need?

Multiply the print size in inches by the DPI you are targeting.

Print size	At 150 DPI	At 300 DPI
4 x 6 inches	600 x 900	1200 x 1800
8 x 10 inches	1200 x 1500	2400 x 3000
A4 (8.27 x 11.7 in)	1240 x 1754	2480 x 3508
A3 (11.7 x 16.5 in)	1754 x 2480	3508 x 4961
Business card (3.5 x 2 in)	525 x 300	1050 x 600

If your image has fewer pixels than the 300 DPI column, relabelling it will not help. Either print smaller, accept 150 DPI (perfectly acceptable for anything viewed at more than arm's length, including most posters), or start from a higher-resolution original.

Label only, or resample?

Label only changes the recorded resolution and leaves every pixel untouched. The file is byte-identical apart from a few resolution fields, so there is no quality cost at all. The physical print size changes. This is what a printer asking for "300 DPI" almost always means.

Resample adds or removes pixels so the image prints at the same physical size at the new resolution. Going from 72 to 300 DPI this way multiplies the pixel count by more than seventeen, all of it interpolated from data that was never captured. The file gets much larger and the image gets softer. It is occasionally the right answer, but it is rarely what people want when they arrive here.

DPI and PPI

Strictly speaking, PPI (pixels per inch) describes a digital image and DPI (dots per inch) describes the ink dots a printer physically places on paper — and a printer typically uses many ink dots to reproduce one image pixel.

In everyday use the two terms are interchangeable, and every image editor labels the field one way or the other without meaning anything different by it. This tool writes the field both terms refer to, so whichever your printer asks for, this is it.

How to change the DPI of an Image

Drop an image onto the box above.
Choose a DPI, or type your own. 300 is standard for print, 72 or 96 for screens.
Decide between metadata only, which keeps the pixels untouched, and resample, which changes the actual pixel dimensions.
Check the print size shown in inches and centimetres, then download.

Limits worth knowing

Every tool has boundaries. These are this one's, stated plainly so you do not waste time discovering them yourself.

Changing DPI alone does not add detail. A 500 x 500 image tagged as 300 DPI is still 500 x 500 pixels and will print at just over 4 cm across.
WebP files have nowhere to store DPI. Convert to JPG or PNG first if you need a print resolution setting.
Some print services ignore the embedded value entirely and work purely from pixel dimensions and your chosen paper size.

Frequently asked questions

Why did my DPI change not work in Photoshop?

Almost always because the tool you used wrote only the JFIF density field and left the EXIF resolution fields untouched. Photoshop reads the EXIF values and shows the old number. This tool writes both, and inserts the JFIF header if the file does not have one, so the value is consistent everywhere.

Does DPI affect image quality?

On its own, no. DPI is a note attached to the file saying how large it should print. The actual quality comes from the pixel dimensions. An image is not improved by relabelling it — what matters is having enough pixels for the size you want to print.

How many pixels do I need for a 300 DPI print?

Multiply the print size in inches by 300. A 4 x 6 inch photo needs 1200 x 1800 pixels. An A4 page at 300 DPI needs about 2480 x 3508. The tool shows you the resulting print size as you change the setting.

What is the difference between metadata only and resample?

Metadata only changes the label and leaves every pixel exactly as it was, so the file is unchanged in quality and the print size changes. Resample actually adds or removes pixels to keep the physical size the same at the new DPI. For a printer asking for 300 DPI, metadata only is nearly always what they mean.

What is the difference between DPI and PPI?

Strictly, PPI describes pixels in a digital image and DPI describes ink dots a printer places on paper. In everyday use, and in every image editor, the two are used interchangeably for the number stored in the file. This tool writes the field that both terms refer to.