Does changing DPI improve image quality?

No, and nothing else does either. DPI is a label saying how large the existing pixels should print. Changing it from 72 to 300 does not add detail — it tells the printer to lay the same pixels down more densely, so the print comes out smaller and sharper.

Does this re-compress my photo?

No. Only the resolution field is rewritten, so a handful of bytes change and the compressed image data is copied through untouched. There is no quality loss whatsoever.

Why does my printer say the image is low resolution?

Because it is dividing the pixel count by the printed size. A 1000-pixel-wide image printed at 200mm works out at about 127 DPI. Setting the field to 300 does not change that arithmetic — you need either more pixels or a smaller print.

Where is DPI stored in a JPEG?

In two places: the JFIF header near the start of the file, and the EXIF resolution tags. They can disagree, which is why programs sometimes report different numbers for the same photo. This page writes both.

Set Image DPI

The print shop wants 300 DPI and your photo says 72. That is one number in the file, not a property of the picture — so this changes it without decoding or re-compressing anything.

Drop a JPEG here

or click to browse

JPEG only • Max 30MB

What DPI actually is

An image is a grid of pixels and nothing more. DPI — dots per inch — is a note attached to that grid saying how densely it should be printed. It has no effect on screen and changes nothing about the picture.

A 1200×1800 photograph at 300 DPI prints at 4×6 inches. The same file marked 72 DPI prints at roughly 16×25 inches, from exactly the same pixels, just spread thinner. That is the whole of it.

Why this does not re-compress anything

Almost every online DPI tool decodes your photo, redraws it and encodes it again — costing a generation of JPEG compression to change one number. There is no need for that.

The resolution lives in two small headers, so this page patches those bytes and copies the rest of the file through unchanged. Your EXIF survives, including tags this site does not otherwise read, and the image data is bit-for-bit what you started with.

The honest caveat

Setting 300 DPI does not make a small image printable at a large size. If your photo is 800 pixels wide and you want a 200mm print, that is about 100 DPI of real detail and no label will change it. You need more pixels or a smaller print.

What the label does fix is software guessing wrong — a print shop laying out your photo at four times the intended size because the file never said otherwise.

Which value to use

72 or 96 — screen use. The historical default, and meaningless for anything you are not printing.
300 — the standard for photographic printing and what almost every print service asks for.
600 — fine art printing and documents with small text. Only worth it if you have the pixels to back it up.

Two places, one number

A JPEG can state its resolution in the JFIF header and again in the EXIF tags. Nothing forces them to agree, and when they do not, different programs report different numbers for the same file — a common source of "but Photoshop says it's 300". This page reads both, tells you if they disagree, and writes both when you save.

Frequently asked questions

Why JPEG only?

PNG stores physical size in a different chunk, in pixels per metre, and WebP usually stores none at all. JPEG is where this field matters and where print workflows expect it.

Will the file size change?

Only by a few bytes, and only if a JFIF header had to be added. The picture itself is untouched.

I need specific print dimensions

Work out the pixels you need — millimetres ÷ 25.4 × DPI — and use Resize image, or Passport photo which does that arithmetic for you.

Related tools

Passport photo — exact millimetres, DPI and file size together
Metadata editor — other EXIF fields, also without re-encoding
EXIF viewer — see everything the file declares