What Makes PDFs Large
PDF file size comes primarily from images. Text, fonts, and structure typically add 100KB-2MB. Images can add gigabytes.
Content Type vs File Size
Typical sizes for different content:
| Content | Pages | Typical Size | Main Factor |
|---|---|---|---|
| Text-only report | 50 | 200KB-1MB | Fonts |
| Document with charts | 20 | 2-10MB | Vector graphics |
| Scanned at 300 DPI | 10 | 5-30MB | Image resolution |
| Photo album | 20 | 50-200MB | Image count and size |
| Architectural plans | 5 | 10-100MB | High-res scans |
Why Scanned Documents Are Huge
A single 300 DPI letter-size page scan is approximately 8.5 × 11 × 300² = 8.4 million pixels. At 24-bit color, that's 25MB uncompressed per page. JPEG compression typically reduces to 500KB-2MB per page.
Compression Strategies by Content Type
Different approaches for different documents:
- •Photo-heavy: JPEG quality reduction (often 50-70% size reduction)
- •Text scans: Convert to black & white JBIG2 (can reduce 10x)
- •Mixed content: Optimize images only, preserve text quality
- •Digital documents: Remove duplicate resources, subset fonts
Resolution Guidelines
Higher isn't always better:
| Use Case | Recommended DPI | Notes |
|---|---|---|
| Screen viewing | 72-150 | Higher is wasted |
| Office printing | 150-200 | Good balance |
| Professional printing | 300 | Standard quality |
| Archival scanning | 300-600 | Preservation priority |
When Not to Compress
Some documents shouldn't be compressed:
- •Legal documents requiring exact reproduction
- •Archival copies (use PDF/A)
- •Already-compressed files (minimal gain)
- •Documents for professional printing
Related Tools
FAQ
Can compression damage my PDF?
Lossy compression reduces image quality. Text remains sharp. Always keep the original until you verify the compressed version meets your needs.
Why did compression barely reduce size?
Text-only PDFs and already-compressed images have little to compress. The file may already be optimized.
Is there a minimum practical size?
Text-heavy PDFs bottom out around 50-100KB. Below that requires removing content.