How to Scan a Document for Upload: Small File, Still Legible
Updated · PixKB
Portals want scanned documents (degree certificates, ID cards, experience letters) as small files, often under 100–500 KB, that are still clearly readable. A raw phone photo of a page is often 2–5 MB. Most of that gap can be closed with how you scan, before you compress anything.
Step by step
- Put the page on a dark, plain surface in daylight or even light. Avoid the flash: it makes a bright spot.
- Scan with a document-scanner app rather than the plain camera: Notes or Files on iPhone (Scan Documents), or Google Drive on Android (tap the Camera button). They find the page edges, straighten it and even out the light.
- Check the scan: corners straight, nothing cut off, text sharp, no shadow from your hand or phone.
- Save as PDF if the portal asks for PDF (and for several pages), or as JPG for a single page if it asks for an image.
- Compress to the portal's limit: PDF compressor for PDFs, exact-KB compressor for images.
Crop to the page: measured
We photographed a printed form lying on a table, then compressed it as the whole photo and cropped to the page:
| Same photo | At 100 KB | At 200 KB |
|---|---|---|
| Whole scene (form, table and a mug) | 991×1487 px | 1548×2322 px |
| Cropped to the form first | 1146×1055 px | 1820×1676 px |
Cropped, the form itself got more pixels at both sizes, because the table and mug no longer used part of the limit. At 100 KB, headings and most text on the cropped form were legible; the smallest print was soft. Scanner apps crop to the page automatically, which is a big part of why they help.
Greyscale: helps colourful documents, not plain ones
Greyscale is often sold as a magic size fix. We measured it. On a colourful certificate (tinted background, coloured border and seal), the greyscale scan was 17% smaller than the colour one, and after compressing both to 100 KB the greyscale version kept about 8% more resolution (1175 vs 1091 pixels). On ordinary documents (black text on white paper) it made almost no difference: 9% smaller before compression and the same size after. So use greyscale when the paper itself is colourful and colour carries no meaning. Don't expect it to rescue a file that is several times over the limit; resolution, cropping and page count matter far more.
Keep colour when it matters: a coloured stamp or seal, a photo on an ID card, or a portal that asks for colour scans.
Resolution: what the numbers mean
Scanner DPI is the number of pixels per inch of paper. For a full page:
| Scan resolution | A4 page | US Letter page | Good for |
|---|---|---|---|
| 300 DPI | 2480×3508 px | 2550×3300 px | Fine print, small stamps, signatures that must stay sharp |
| 200 DPI | 1654×2339 px | 1700×2200 px | Ordinary typed documents and certificates |
| 150 DPI | 1240×1754 px | 1275×1650 px | Large, clear text when the KB limit is tight |
Pixels = size in inches × DPI. A phone scanner app picks its own resolution; what matters is the pixel size of the final file, which the compressor reduces to fit your limit.
At tight limits the compressor reduces the pixel size for you, so you rarely need to set a DPI by hand. If a portal states a scan resolution (for example "200 DPI"), scan at that or resize to the matching pixels.
Several pages
If the portal wants one file with several pages, combine them into one PDF with JPG to PDF or merge PDF, which can both build the file under a size limit. Each extra page shares the same limit, so a 4-page document at 200 KB has about 50 KB per page; see combining documents into one PDF.
Common mistakes
- Photographing at an angle. The text shrinks towards the far edge. Hold the phone parallel to the page, or use a scanner app.
- Uploading a screenshot of a scan. It's lower resolution than the scan itself.
- Scanning at 600 DPI "to be safe". Four times the pixels of 300 DPI, and they're thrown away again when you compress.
- Including pages the portal didn't ask for. They use part of the limit.
- Sending an iPhone HEIC photo. Many portals reject it; convert it with HEIC to JPG, or let the compressor do it.
Frequently asked questions
PDF or image for a scanned document?
Use what the portal asks for. If it accepts both: a single page as JPG, several pages as one PDF.
What resolution should I scan at?
200 DPI suits most typed documents; 300 DPI for fine print or small stamps. If the portal states a DPI, use that.
My scan is still too big. What now?
Compress it to the exact limit; that does more than any scan setting. If it still can't fit readably, crop to the page and remove pages the portal didn't ask for.
Does greyscale make the file smaller?
For colourful paper, yes: 17% smaller in our test. For black text on white paper, hardly at all.
Will my document be readable at 100 KB?
For a single page cropped to its edges, mostly yes: in our test, headings and most text stayed legible and only the smallest print went soft.
Why does the portal say my file is invalid?
Usually the format: it wants JPG or PDF and got something else, such as an iPhone HEIC. Convert it first.
Is my document uploaded to PixKB?
No. Compression and conversion happen in your browser, on your device.