The limits everyone runs into
Almost every portal has its own cap per attachment — and often names it only when the upload fails. Typical values from practice:
| Portal type | Usual limit |
|---|---|
| Tax portal (receipts, proofs) | usually 10 MB per file, depending on the form |
| Job application portals (corporations) | often 2–5 MB per document, sometimes 10 MB total |
| Health-insurer apps | 5–10 MB per submission |
| University applications | frequently 2–4 MB per file |
| Email attachment (safe value) | under 10 MB total |
A single 600-dpi color scan blows past many of these limits on its own. Yet the high resolution is completely unnecessary for the purpose — the clerk reads the document on screen, not under a magnifying glass.
The 3-minute way under any limit
- Bring the page height to ~1600 pixels. That's about 135 dpi at A4 — crisply legible on screen. Drag the scan (JPG/PNG) into the resize tool, set the long edge to 1600 px. It runs in the browser, the document doesn't leave your computer — for payslips and IDs that's not a detail but the point.
- Save as JPG at quality 75–80. Text handles that without trouble. A 12 MB scan then typically lands at 300–600 KB.
- For multiple pages: optimize first, then bundle to PDF. The order is decisive — a PDF from raw scans stays huge. How to bundle with built-in tools is in Creating a PDF from images.
Real example: six payslips, scanned at 600 dpi = 41 MB. After steps 1–3: 1.8 MB — and indistinguishable from the original on the monitor.
When the document is photographed instead of scanned
A phone photo of the contract is completely legitimate — with three rules: photograph straight from above (angled shots look unprofessional and are hard to read), daylight without a cast shadow from your own hand, and ideally use the built-in scan function: iPhone Notes app → scan documents, Android Google Drive → Plus → Scan. Both straighten the perspective, raise the contrast, and deliver a PDF directly.
Watch the metadata: phone photos contain GPS coordinates. For uploads to strangers, remove it first with the metadata editor — harmless with official portals, relevant with classifieds or forums.
Grayscale: the underrated lever
Most documents are black on white — yet many scan in color. A grayscale scan is only a third as big at the same resolution, and a true black-and-white scan (1 bit) drastically smaller again. When color stays mandatory: IDs, certificates with colored seals/stamps, and anything where the portal explicitly demands color scans.
What you shouldn't do
- Insert the document into Word and export as PDF. A classic detour that often enlarges the file and degrades the quality.
- Re-save as JPG multiple times. Each round adds artifacts. Scale once, compress once, done.
- Anonymous online compressors for sensitive documents. Uploading payslips to a third-party server to get around an upload limit trades a small problem for a bigger one. Browser-local tools do the same without any transfer.
- Shrinking below the legibility limit. Below ~1200 px page height, footnotes and stamps become critical. Better close to the limit than illegible — rejected documents cost more time than any upload.
Frequently asked questions
Why is my scan so big?
Usually because of too-high scan resolution. 600 dpi in color quickly produces 10 to 30 MB for an A4 page. For documents, 150 to 200 dpi is completely enough — that's a tenth of the data at identical on-screen legibility.
Which format is smallest for scanned documents?
For text documents: JPG at quality 75 to 80, or smaller still as a grayscale scan. PDF is usually just the container — what matters is how the images inside are compressed. A PDF from optimized JPGs is many times smaller than one from raw scans.
How small can I make a document before it becomes illegible?
Rule of thumb: the text lines should be at least 20 to 25 pixels tall in the image. For an A4 page that's about 1200 to 1600 pixels of page height. Below that, small font sizes and stamps become critical.
Do official portals also accept photos instead of scans?
Usually yes, as long as the document is complete, straight, and legible. Important: good light, photograph straight from above, and use the scan function of the Notes app (iPhone) or Google Drive (Android) — which straightens the perspective automatically.
Sources
Apple — Scan documents with the Notes app · Google — Scan with Drive.