What Is DPI?
DPI stands for dots per inch. When converting PDF to images, DPI determines how many pixels represent each inch of the original document. Higher DPI produces more pixels, resulting in sharper images but larger file sizes.
A standard A4 PDF page (8.27 × 11.69 inches) produces these image dimensions at different DPI settings:
| DPI | Pixel Dimensions (A4) | Approx. File Size | Best For |
|---|---|---|---|
| 72 DPI | 595 × 842 | ~85 KB | Screen previews, email attachments |
| 150 DPI | 1240 × 1754 | ~350 KB | General web use, e-readers |
| 200 DPI | 1654 × 2339 | ~600 KB | Default — balanced quality/size |
| 300 DPI | 2480 × 3508 | ~1.4 MB | Print quality, industry standard |
| 600 DPI | 4960 × 7016 | ~5.5 MB | High-res printing, fine detail, OCR |
Key rule: Doubling the DPI roughly quadruples the file size (and pixel count). Going from 150 DPI to 300 DPI produces 4x more pixels.
DPI Comparison: When to Use Each Setting
72 DPI — Screen Previews
72 DPI matches the original resolution of early computer displays. It produces small, fast-loading images suitable for email attachments, quick document previews, and thumbnail generation. Text is readable but may appear slightly soft. Not suitable for printing.
150 DPI — Web Sharing
150 DPI is the sweet spot for web-quality images. Text is crisp and readable on screen. Images are small enough for email and messaging apps. This is the recommended setting for sharing document pages on social media, chat apps, or embedding in blog posts.
200 DPI — Default (Balanced)
200 DPI is our converter's default setting. It produces clear, sharp images suitable for both screen viewing and basic printing. Text rendering is clean, and the file sizes are reasonable. This is the best all-purpose setting if you are unsure which DPI to choose.
300 DPI — Print Quality (Industry Standard)
300 DPI is the industry standard for printed documents. At typical reading distance (12–18 inches), the human eye cannot distinguish individual dots at 300 DPI. This setting is recommended for:
- Office printing (reports, handouts, brochures)
- Archival copies of important documents
- Images that may be cropped or zoomed
- OCR processing (minimum recommended DPI)
600 DPI — High-Resolution
600 DPI is overkill for most purposes but essential for specific use cases: professional printing with fine text or detailed line art, high-accuracy OCR on dense or small-font documents, and archival preservation where future use cases are unknown. File sizes are significantly larger.
Use Case Recommendations
| Use Case | Recommended DPI | Why |
|---|---|---|
| Email attachment | 150 DPI | Small files, readable text |
| Social media sharing | 150–200 DPI | Good quality, fast loading |
| Web publishing | 200–300 DPI | Sharp on high-DPI screens |
| Office printing | 300 DPI | Industry standard, crisp text |
| Professional printing | 300–600 DPI | Maximum detail for fine text |
| OCR processing | 300 DPI (600 preferred) | Higher accuracy recognition |
| Archival | 600 DPI | Future-proof, maximum quality |
File Size Impact
Understanding the file size implications of each DPI setting helps you make informed decisions, especially when processing multi-page PDFs:
| DPI | 1-Page PDF | 10-Page PDF | 50-Page PDF |
|---|---|---|---|
| 72 | ~85 KB | ~850 KB | ~4.2 MB |
| 150 | ~350 KB | ~3.5 MB | ~17 MB |
| 200 | ~600 KB | ~6 MB | ~30 MB |
| 300 | ~1.4 MB | ~14 MB | ~70 MB |
| 600 | ~5.5 MB | ~55 MB | ~275 MB |
Tip: For large multi-page PDFs, start with 200 DPI. If the quality is insufficient for your needs, re-convert at 300 DPI. There is rarely a reason to use 600 DPI unless you are doing professional printing or OCR.
DPI vs JPEG Quality
DPI and JPEG quality are two separate settings that both affect output quality. DPI controls the number of pixels (resolution). JPEG quality controls how much those pixels are compressed.
Our converter uses 90% JPEG quality by default. At this setting, compression artifacts are invisible to the naked eye. Reducing JPEG quality to 75% cuts file size by roughly 40% with minor quality reduction visible only when zooming in on text edges.
For the sharpest possible text rendering, use PNG output instead of JPG. PNG uses lossless compression, producing larger files but with zero compression artifacts around text characters.