The DPI tag is metadata: real resolution is a division you can do yourself
Nearly every argument about whether a file is printable turns on a number stored in the file's header — and that number can be edited without touching a single pixel. A file tagged 300 DPI may hold 400 pixels; a file tagged 72 DPI may hold 6,000. The tag records an intention. What the press consumes is the pixel count against the ordered width, and that is a division anyone can run.
The width your image editor reports — not the file size in MB
Common placements
Enter a pixel width to see the numbers.
| What the tag stores | an intended physical size, editable without changing the image |
|---|---|
| What the press consumes | pixel count divided by the width actually ordered |
| A 1,024 px file printed at 21 cm | 124 DPI, whatever the header says |
| A 2,000 px file printed at 25 cm | 203 DPI, whatever the header says |
| Only case where the tag is meaningful | when nobody has specified a print width at all |
Where the number in the header comes from
Whatever software last wrote the file put it there, usually copying a default. Scanners record what they scanned at; phone cameras write 72 because a display is the assumed destination; export dialogs write whatever sat in the box. None of them knew the width this job would be printed at.
The division, once
Effective resolution is pixel width divided by print width in inches. If it helps, print width in centimetres divided by 2.54 gives inches. Nothing else enters the calculation — not the tag, not the file size in megabytes, not the format.
What a shop can do with this in a message
It converts an argument about quality into a question about a number, which is easier for both sides.
- Ask for the pixel dimensions, not the DPI
- State the print width you were asked for, in centimetres
- Send back the division rather than a verdict
FAQ
- Should the tag be corrected before printing?
- It changes nothing the press reads when a width has been specified. Correcting it is tidy and does not alter the outcome.
- Why do design tools still ask for DPI?
- Because they are also used for fixed-size output like a page, where a physical size is genuinely part of the document.
- Does a large file size mean high resolution?
- No. A lightly compressed small image can be larger on disk than a well-compressed big one.