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Change an image’s DPI

Set the number a form is asking for — and find out what it really means for your print.

or drag it here, or paste it

JPG, PNG, WebP, HEIC, AVIF and BMP. Your file is processed on your device.

How do I change an image’s DPI to 300?

To change an image’s DPI, add it below and choose a value. DPI is a number written into the file’s header: it decides how large the image prints, and changes nothing about the pixels. FileBelow writes it, and also tells you how many pixels your intended print size genuinely needs, because a form that wants 300 DPI and a print shop that wants 300 DPI are asking for two different things.

What DPI actually is

An image file is a grid of pixels. That grid has no physical size — it is a count, not a measurement. A photograph 1800 pixels wide is 1800 pixels wide, and how many inches that turns into depends entirely on how densely something chooses to print them.

DPI is that choice, written down. At 300 dots per inch, 1800 pixels is six inches. At 180, the same 1800 pixels is ten inches. Same file, same pixels, same sharpness on screen — different physical print, because a different density was requested.

So changing the DPI changes the size of the print and nothing else. It cannot make an image sharper, because sharpness at a given physical size is decided by how many pixels you have to spread over it, and that number does not move.

The two people who ask for 300 DPI

A form with a validator. Some submission systems — academic journals, certain government portals, a few printing services — literally read the header and reject anything that does not say 300. This is the easy case: the field is the requirement, this tool writes the field, and you are done in ten seconds. Nothing about your image needed to change and nothing did.

A person who wants a good print. When a designer or a printer asks for 300 DPI, they are using shorthand for “enough pixels that this looks sharp at the size we are printing it”. Writing 300 into the header of a 600-pixel image satisfies the words and not the request: it now claims to be a two-inch print, and printed any larger it will look exactly as soft as it did before.

The tool handles both, because it writes the number and tells you what your file can actually deliver. If the table says you do not have enough pixels for the print size you want, that is the real answer, and no header edit changes it.

Why some tools quietly enlarge your image instead

A number of DPI converters, given a small image and a request for 300 DPI, will scale the picture up so that the pixel count matches the physical size. The file gets bigger, the header says 300, and the image is blurrier than it was, because the extra pixels were calculated by averaging the ones that already existed.

That is not a fix, it is a way of hiding the problem inside a larger file, and it is worse than doing nothing because it destroys the sharpness the original did have. FileBelow will not do it. If you genuinely want a larger pixel count, the resizer will produce one and will tell you plainly that enlarging cannot add detail that is not there.

DPI, PPI, and why the words are a mess

Strictly, PPI describes pixels in an image and DPI describes dots of ink a printer puts down, and a printer lays several dots per pixel. In practice every piece of software, every form and every help page uses DPI for both, so this page does too — arguing about the terminology with someone who has already rejected your file is not a winning move. The longer explanation covers where the distinction genuinely matters.

Common questions

Does changing DPI improve image quality?
No. Not a little, not in some cases — not at all. DPI is a number in the file’s header saying how large the image should print. Changing it from 72 to 300 changes two bytes and leaves every pixel exactly as it was. If an image looks soft at 72 DPI it will look identically soft at 300 DPI, printed at the same physical size.
A form says my image must be 300 DPI. Will this satisfy it?
If the form is checking the header field, yes — that is what this writes, and it is the whole fix. If a human at a print shop is asking, they almost certainly mean "give me enough pixels for a sharp print at this size", which is a different request that this tool cannot grant and will instead tell you the size of. The table on the page shows the pixel count your intended print size genuinely needs.
How many pixels do I need for a 300 DPI print?
Multiply the print size in inches by 300. A 6×4 inch photo needs 1800×1200 pixels; a 10×8 needs 3000×2400; an A4 page needs roughly 3500×2480. The tool works this out for your file and says whether it has enough. If it does not, the only real fix is a higher-resolution original — enlarging invents detail rather than recovering it.
Why can’t I set the DPI on a WebP file?
Because WebP has no standard field for it. JPEG carries density in its JFIF header and PNG in a pHYs chunk; WebP simply has nowhere to put the number. Choosing WebP here switches the output to JPEG for that reason, and if you override it the page tells you the setting was not written rather than pretending it was.
What DPI should a web image be?
It does not matter, because browsers ignore the field entirely. A web image is measured in pixels and displayed in pixels. The widespread advice that web images should be "72 DPI" is a leftover from 1980s Macintosh screens and has been meaningless for decades — an image at 300 DPI displays identically on every website.