PDF to JPG: which resolution (DPI) should you choose?
When you convert a PDF page to an image, you are usually asked to pick a resolution, often 72, 150 or 300 DPI. The choice decides how sharp the image is, how many pixels it has and how big the file gets. This guide explains what the number really means and which setting suits which job.
What DPI means when converting a PDF
A PDF page does not have pixels. It has a physical size, such as A4 or US Letter, and its text and drawings are usually described as shapes that can be drawn at any scale. Turning a page into a JPG or PNG means "rendering" it: drawing it onto a grid of pixels.
DPI (dots per inch) tells the converter how fine that grid should be. At 150 DPI, every inch of the page becomes 150 pixels. So the pixel size of the image is simply:
page width in inches × DPI, and page height in inches × DPI
Strictly speaking, the term for screens and images is PPI (pixels per inch), but DPI is the label most tools use, and for this purpose they mean the same thing.
A higher DPI gives more pixels, more detail and a larger file. A lower DPI gives fewer pixels, a smaller file and less detail. Note that the DPI setting cannot add detail that is not there: if the PDF contains a low-resolution photo or a rough scan, rendering at 300 DPI just produces a large image of a blurry picture. Vector text and graphics, on the other hand, get sharper as DPI rises.
Pixel dimensions for A4 and Letter pages
An A4 page is 210 × 297 mm, about 8.27 × 11.69 inches. A US Letter page is 8.5 × 11 inches. Multiplying by the DPI gives these image sizes in portrait orientation (rounded to whole pixels):
| DPI | A4 (8.27 × 11.69 in) | Letter (8.5 × 11 in) | Approx. megapixels |
|---|---|---|---|
| 72 | 595 × 842 px | 612 × 792 px | about 0.5 MP |
| 150 | 1240 × 1754 px | 1275 × 1650 px | about 2.1–2.2 MP |
| 300 | 2480 × 3508 px | 2550 × 3300 px | about 8.4–8.7 MP |
Two things stand out. First, 72 DPI matches the PDF's own unit of measurement (a point is 1/72 inch), which is why an A4 page is often described as 595 × 842 points. Second, doubling the DPI quadruples the pixel count: a 300 DPI image has four times as many pixels as a 150 DPI one, and more than seventeen times as many as a 72 DPI one. File size grows roughly in step, though the exact size depends on the content and the format.
For landscape pages, simply swap width and height.
Which DPI to choose
72 DPI: thumbnails and quick previews
About 600 × 800 pixels is enough to see the layout of a page but small text will be hard to read, especially on high-density phone and laptop screens that pack many pixels into each inch. Use 72 DPI for thumbnails, previews in a gallery or a rough visual reference where file size matters most.
150 DPI: screens, slides and sharing
At around 1240 × 1754 pixels for A4, a full page is readable on most screens, and a slide or chart pasted into a presentation looks clean when shown at normal size. This is a sensible default for web pages, chat messages, presentations and social posts. Many social networks resize uploaded images to roughly 1000–2000 pixels on the long side anyway, so anything much larger is often scaled down after upload.
300 DPI: print and detail
300 DPI is the long-standing rule of thumb for printing images at their original size with fine detail. Choose it if the image will be printed, if people will zoom in to read small print or technical drawings, or if you plan to crop part of the page and still want it sharp. It is also a common recommendation when the image will be fed into text recognition (OCR) software elsewhere, since higher resolution generally helps recognition of small characters.
JPG or PNG?
The format matters as much as the resolution. JPG and PNG compress images in completely different ways.
| JPG | PNG | |
|---|---|---|
| Compression | Lossy: discards detail the eye is less likely to notice | Lossless: every pixel is kept exactly |
| Best for | Photos, scans of photos, pages with gradients and lots of colour | Text, line art, charts, screenshots, diagrams |
| Typical file size | Small for photographic content | Small for flat colours and sharp edges, large for photos |
| Artefacts | Can show smudges or halos around sharp text | None |
| Transparency | Not supported | Supported |
A rule of thumb: if the page is mostly photographs, use JPG. If it is mostly text, tables or diagrams on a plain background, PNG often gives crisper results and, perhaps surprisingly, may not be much bigger, because large areas of identical colour compress very efficiently in PNG. For a page that mixes both, try each and compare.
About transparency: a rendered PDF page normally has a white background, so even a PNG will usually be opaque. Transparency matters more when you work with the image in a design tool afterwards.
Common use cases
- Putting a page into a slide deck. 150 DPI, PNG for charts and text, JPG for photo-heavy pages.
- Posting a flyer or poster on social media. 150 DPI JPG is usually enough. Check the platform's recommended dimensions.
- Sending a page in a chat app. 150 DPI JPG. Many messaging apps compress images again, so 300 DPI rarely helps.
- Printing a page as a photo or handout. 300 DPI.
- Running OCR in other software. 300 DPI, PNG if the file size is acceptable, since JPG artefacts around letters can confuse recognition.
- Making thumbnails for a website or archive. 72 DPI JPG.
A note on file size
Converting a 50-page PDF to 300 DPI PNG images can easily produce hundreds of megabytes, because each image may be several megabytes. If you only need a few pages, extract those pages first and convert just them. And if the goal is simply a smaller PDF, converting to images is the wrong route; compression is designed for that, as explained in how to reduce a PDF's file size.
Also remember that an image of a page is just pixels: you can no longer select or search the text in it, and links stop working.
Doing it on FlexyFiles
- Open PDF to JPG and upload your PDF.
- Choose the format, JPG or PNG, and the resolution: 72, 150 or 300 DPI.
- Enter a name under "Save as" and click Run. Every page is converted, and the images are delivered together as a ZIP file in "Your files", ready to download.
If you need only some pages, first use Extract pages to create a smaller PDF and convert that. In the full workspace at /pdf/app you can work with the same files across several tools without uploading them again. Going the other way, images can be turned back into a PDF with JPG to PDF. Rendering happens on FlexyFiles' servers, so even 300 DPI conversions of long documents work on a phone.