Some upload forms have very strict limits — 100KB, 300KB, even 50KB. Standard compression tools are designed to reduce file size, not hit a specific target. This guide explains how to reliably reach specific file size targets, what's actually achievable, and when a target is technically impossible without sacrificing legibility.
Before spending time trying to hit a specific target, it helps to know what's physically possible for different document types:
| Document type | Minimum achievable size | Notes |
|---|---|---|
| Single page, text only (typed letter, form) | 10–50KB | No image data — text is tiny |
| Single page scan at 72 DPI grayscale | 30–80KB | Very low quality but legible |
| Single page scan at 150 DPI grayscale | 50–200KB | Good quality, clear text |
| Single page IC copy (colour scan) | 80–200KB | Depends on scan settings |
| Multi-page payslip (3 pages, 150 DPI grayscale) | 150–400KB | Typical after good compression |
| 10-page transcript (colour scan) | 500KB–1.5MB | Hard to go below without degradation |
The key insight: a single page of a scanned document at acceptable quality is typically 50–200KB. Multi-page documents multiply this. If you need an entire 10-page document under 100KB, that's 10KB per page — which is only achievable at very low quality that may not be legible. In that case, the target is unrealistic and you should contact the portal to ask for an alternative.
Start here — it's the fastest approach and often sufficient for targets of 500KB or higher.
Go to shrinkpdf.fyi, upload your PDF, and select Maximum compression.
Download and check the file size. If it meets your target, you're done. If not, continue to the next methods.
For targets under 200KB per page, re-scanning is more effective than compression. Here are the settings to use for specific targets:
In Microsoft Lens: set document quality to "Normal". In CamScanner: Settings → Scan Quality → Standard (approximately 150 DPI). Most scanner apps don't expose DPI directly — "Normal" or "Standard" quality is typically 150–200 DPI.
If you only need to submit one specific page from a multi-page document (e.g. the first page of a bank statement, or the signature page of a contract), extracting that single page dramatically reduces the file size.
Ghostscript's /screen setting is the most aggressive compression available from any free tool. It targets 72 DPI — the minimum for screen legibility — and produces the smallest possible output.
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
Install Ghostscript free: Windows → ghostscript.com, Mac → brew install ghostscript, Linux → sudo apt install ghostscript
Ghostscript /screen typically achieves 10–20% better compression than browser-based tools on the same file — useful when you're close to but not quite at your target.
If your PDF contains colour scans and you're struggling to meet a size target, converting to grayscale before compression can yield significant additional reduction. Colour images store three data channels per pixel; grayscale stores one.
Ghostscript can convert to grayscale and compress in one step:
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
Only realistic for: single-page text documents (typed letters, simple forms). For scanned documents, 50KB per page requires 72 DPI which produces visibly low quality — text is technically legible but not sharp. This target is unrealistic for most real-world document submissions.
Achievable for: single-page scans at 96–100 DPI grayscale. Suitable for simple text documents, plain forms, basic ID copies. Use Ghostscript /screen or re-scan at lowest quality setting. Not suitable for certificates with fine detail or colour-important documents.
Achievable for: single-page scans at 150 DPI grayscale, or 2–3 page text documents. This is a reasonable target for most government document uploads. Maximum compression in ShrinkPDF followed by Ghostscript /screen typically achieves this for standard single-page documents.
Achievable for: most single-page documents and short (2–3 page) multi-page documents. Maximum compression in ShrinkPDF is usually sufficient for this target without any re-scanning.
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