DPI — dots per inch — controls how much detail a scan captures, and it is tempting to assume higher is always safer. In practice, most scanning settings default to far more resolution than the document’s actual use requires, which means larger files, slower uploads, and more compression needed later, all for detail that will never be seen on the screen the document is actually read on.
What DPI actually controls
A higher DPI captures more pixels per inch of the original page, which is genuinely useful when you need to zoom in closely or print at high quality. But a screen only displays a limited amount of detail at normal viewing size — scanning far beyond what a screen can show simply produces a bigger file with no visible benefit for on-screen reading.
Recommended settings by use
- 150 DPI — sending or uploading a document that will only ever be viewed on screen: email attachments, portal uploads, general record-keeping. This is enough for comfortable reading and keeps files small.
- 200 DPI — a reasonable middle ground if the document might occasionally be printed at normal size, or if it contains small print you want to be extra safe about.
- 300 DPI — documents you specifically need to print at high quality, or genuinely important archival copies you are keeping long-term.
- 600 DPI and above — reserved for specific professional or archival needs (fine art reproduction, forensic-level detail); rarely necessary for everyday paperwork.
Colour mode matters as much as DPI
Alongside DPI, colour mode has a large effect on file size. A plain text document scanned in colour, when it has no meaningful colour content, wastes significant size for nothing — switching to greyscale or black-and-white for text-only documents can cut the file size dramatically on its own, independent of the DPI setting. Reserve colour scanning for documents where colour genuinely carries information: stamps, photographs, coloured diagrams, official seals.
Working out the right setting for a specific document
- Ask how the document will actually be used — screen only, printed occasionally, or archived long-term.
- Check whether it has any genuinely small print that needs extra resolution to stay legible.
- Ask whether colour carries real information, or whether the document is effectively black text on white paper.
- Pick the lightest setting from the table above that covers your actual need — not the highest one available on the scanner.
If you have already scanned at too high a setting
There is no need to re-scan a document just because it turned out larger than necessary. The PDF Compressor re-encodes the embedded images at a smaller effective size, which achieves much of the same benefit after the fact as scanning lighter would have from the start — useful when the physical document is no longer available to re-scan, or when re-scanning simply is not worth the time for a one-off file.
Setting your scanner’s default sensibly
If your scanner or scanning app currently defaults to 300 or 600 DPI in colour, changing that default to 150–200 DPI in greyscale for routine documents saves you from having to think about the setting every single time, while still leaving the option to switch up manually for the occasional document that genuinely needs archival quality.
Frequently asked questions
Will 150 DPI look blurry on screen?
No, for standard text documents it reads clearly and sharply at normal screen viewing size — the softness only becomes apparent if you zoom in far beyond how the document would normally be read.
Does DPI affect a photographed “scan” from a phone the same way?
Phone photos work on a similar principle, though DPI is not usually a setting you control directly — the resolution is fixed by the camera, so cropping tightly to the document matters more than adjusting a DPI value.
Should I scan important documents at the highest setting just to be safe?
Only if you have a specific reason to need that level of detail. For most everyday paperwork, a moderate setting is genuinely sufficient and saves considerable, unnecessary file size.
Can I change DPI after scanning?
Not upward — you cannot add detail that was never captured. You can effectively reduce it afterwards through compression, which is the practical fix for an oversized existing scan.
Is compressing an already-scanned file free?
Yes. No sign-up, no watermark, and files are removed from the server automatically about an hour after processing.