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What a print shop means by “300 DPI”
DPI is a number written in the file’s header, not a property of the pixels. A 3000 × 2000 photo has 3000 × 2000 pixels whether it is tagged 72 or 300. What the tag decides is the physical size the file claims when it is placed into a print layout: at 72 DPI those 3000 pixels ask for 105 cm of paper, at 300 DPI they ask for 25 cm.
So when a print shop, a marketplace or a journal rejects your file for “not being 300 DPI”, one of two completely different things is happening. Usually it is the first, and it takes five seconds to fix:
- The tag is wrong. Your pixels were always sufficient; the file just says 72, because phones, screenshots and most web tools write 72 by default. This is what this page fixes.
- The pixels are genuinely too few for the size you want printed. No tool can fix that — re-tagging a small image as 300 DPI makes it claim to be print-ready while printing at the size of a stamp.
The tool below tells you which of the two you have, before you send the file back.
How many pixels 300 DPI actually needs
This is the table the argument is usually about. If your image has at least this many pixels, tagging it 300 DPI is honest and your file will print at that size properly.
| Printed size | Millimetres | Pixels needed at 300 DPI |
|---|---|---|
| A3 | 297 × 420 | 3508 × 4961 |
| A4 | 210 × 297 | 2480 × 3508 |
| A5 | 148 × 210 | 1748 × 2480 |
| US Letter | 216 × 279 | 2550 × 3300 |
| Photo 10 × 15 cm | 100 × 150 | 1181 × 1772 |
| Business card | 85 × 55 | 1004 × 650 |
A 12-megapixel phone photo is roughly 4000 × 3000 pixels, which comfortably covers A4 at 300 DPI. A screenshot from a laptop is often 1440 × 900, which does not — it covers about 12 × 7.6 cm. Re-tagging it will not change that, and the tool says so rather than letting you find out at the counter.
What this tool does to the file
It rewrites the density field and copies every other byte through untouched. There is no re-encode, so a JPEG does not lose another generation of quality and a PNG stays pixel-identical. The file that comes back is the file you put in, with a corrected label.
For JPEGs it writes the value in both places a JPEG can declare one — the JFIF header and the EXIF resolution tags. Skipping the second is the classic bug in DPI converters: the JFIF header says 300, Photoshop reads EXIF, still shows 72, and the file gets rejected a second time.
Nothing is uploaded. The file is read into memory by this page, edited there, and handed back as a download — disconnect from the network after the page has loaded and it still works.
What it does not do
It does not add pixels, sharpen, upscale or “enhance”. Any tool promising to raise the DPI and the quality of an existing photo is either resampling — inventing pixels that were never photographed — or describing the tag change in flattering language. This one changes the tag and tells you exactly what that is worth.
How to convert an image to 300 DPI
The target is already set to 300 on this page, so there is nothing to configure.
Step 1: Drop your JPG or PNG in
Drag the file onto the box above, or click to pick it. Several files at once are fine — they come back as a ZIP.
Step 2: Read what the file currently declares
The panel shows the density the file claims today, its pixel dimensions, and the size it will print at 300 DPI. If those pixels do not cover the paper you need, it warns you here rather than after printing.
Step 3: Convert and download
Press the button. The file is rewritten in your browser and downloads immediately, named with a `_300dpi` suffix so you can tell it from the original.
Frequently Asked Questions
Will converting to 300 DPI make my photo look better?
No. The pixels are identical before and after — only the file’s claim about its own print size changes. If a photo looks soft on screen it will look soft on paper, at any DPI tag.
My print shop still says the file is low resolution. Why?
Because it is: the tag is now right but the pixel count is genuinely too low for the size you asked for. Check your pixels against the table above. The only real fixes are re-shooting, re-scanning at a higher setting, or printing smaller.
Does this work on PNG as well as JPG?
Yes. PNGs store density in a `pHYs` chunk, which is written the same way. WebP and AVIF have no comparable field, so they are not accepted rather than silently ignored.
Is 300 DPI always the right number?
For photographs printed on paper, almost always — commercial presses screen at 150–175 lines per inch and 300 is the conventional double. Line art, scans and engraving often want 600; see the 600 DPI page. Anything shown only on a screen ignores the tag completely.
Are my files uploaded anywhere?
No. This project contains no API route that accepts a file. Everything runs in your browser, and nothing about the file — not its name, not its size — is sent anywhere.
Related Tools
- Convert an Image to 600 DPISet a file to 600 DPI without re-encoding it — and find out first whether 600 is what your job actually needs.
- Check the DPI of an ImageFind out what your file really declares — including the case where a JPEG declares two different values at once.
- Image DPI Converter (72 to 300 DPI)Set the DPI your print shop asked for, and see the size the file will actually print at.