How to convert PDF pages to JPG at the right resolution

A PDF page has no pixel size. It is described in points, 72 to the inch, and turning it into a JPG means deciding how many pixels each inch becomes. Every other choice in the conversion is minor next to that one, so this guide spends most of its time on it.

PDF to JPG, step by step

1. Open PDF to JPG and choose Add a PDF, or drop the file onto the page. A thumbnail of every page appears. If the document has a password, type it into the box that appears and confirm it.
2. Choose a resolution: 72 dpi, 150 dpi or 300 dpi. 150 is selected to begin with.
3. Under Format, choose JPEG or PNG. The panel tells you how many images will be made, one per page.
4. Press the PDF to JPG button. A one-page document downloads as a single image named after the file, such as report-001.jpg. A longer one offers every image together as a zip, numbered -001, -002 and so on.

Two terms

Rasterising a PDF is rendering a page described in points into a grid of pixels. Text in a PDF is vector and stays sharp at any zoom; once it has been rasterised it is a fixed grid, and zooming in only makes the pixels bigger.

Dots per inch (dpi), in this tool, is the number of pixels each inch of the page becomes. Because a PDF measures in points, the page is drawn at a scale of dpi ÷ 72: one pixel per point at 72 dpi, 2.08 at 150 and 4.17 at 300.

What each resolution gives an A4 page

An A4 page is 210 × 297 mm. At 25.4 mm to the inch that is 210 ÷ 25.4 = 8.27 inches by 297 ÷ 25.4 = 11.69 inches, and the pixel size is those inches multiplied by the dpi. At 300 dpi: 210 ÷ 25.4 × 300 = 2480.3, so 2480 pixels across, and 297 ÷ 25.4 × 300 = 3507.9, so 3508 down.

Resolution	Scale (dpi ÷ 72)	A4 page in pixels	Total pixels	Against 150 dpi
72 dpi	1	595 × 842	0.50 million	0.23 ×
150 dpi	2.08	1240 × 1754	2.17 million	1 ×
300 dpi	4.17	2480 × 3508	8.70 million	4.0 ×

The last column is the one people miss. Resolution is measured along one edge, but an image has two. Going from 150 to 300 dpi doubles the width and doubles the height, so the pixel count goes up 2 × 2 = 4 times: 2480 × 3508 = 8,699,840 against 1240 × 1754 = 2,174,960. Going from 72 to 150 multiplies each edge by 2.08, and 2.08 × 2.08 = 4.34. That squaring is why the 300 dpi option carries the note that its files are roughly four times the size of 150. There is no hidden quality setting behind the jump; it is all pixel count.

For a US Letter page, 8.5 × 11 inches, the same sum at 300 dpi gives 8.5 × 300 = 2550 by 11 × 300 = 3300 pixels.

One small difference from the table: the tool starts from the page size recorded in the file, in points, and rounds each edge up to a whole pixel. The A4 size this site’s own PDF tools write is 595.28 × 841.89 points, and at 300 dpi that renders as 2481 × 3508, one pixel wider than the millimetre arithmetic.

Choosing, and what goes wrong

• 72 dpi gives the page at its nominal size, one pixel per point. It suits something that will only ever be looked at on a screen at normal size, and text in it will look soft, because type is now part of a grid only 595 pixels across an A4 page.
• 150 dpi is the sensible default for most uses, and the one to keep unless you know otherwise.
• 300 dpi is what print and OCR want. Expect files roughly four times the size of 150.

The thing that goes wrong is expecting the image to be as good as the PDF. It cannot be. Text that was sharp at any zoom now has a fixed resolution, and if sharpness matters more than portability, the honest answer is to keep the PDF.

A few other behaviours are worth knowing before you convert:

• JPEG quality is fixed. There is no quality slider; the tool asks the browser for JPEG at 0.88 on its 0 to 1 scale. Resolution is the only size control.
• PNG comes out opaque. Each page is painted on white before it is drawn, because a PDF page has no background of its own. Choose PNG for exact edges on type and line art, not for transparency.
• Every page is converted. There is no per-page selection yet. To get one page, pull it out with Split PDF first, then convert that.
• Rendering is done by pdf.js, the same engine Firefox uses to display PDFs, running in your tab.

Other ways to do it

On a Mac, Preview can do it a page at a time: go to the page, then File → Export, and choose JPEG or PNG. Export saves the current page only, so a long document means repeating it for every page.

On the command line, poppler’s pdftoppm converts every page in one go, writing page-1.jpg, page-2.jpg and onwards. The -r value is the resolution:

pdftoppm -jpeg -r 150 input.pdf page

Windows has no built-in route on the list we have checked.

Checking that nothing was uploaded

Watch the Network tab of your browser’s developer tools while you work. The requests you will see are the page fetching its own code: the PDF libraries when the file first opens, and a zip library the first time you download several images at once. None of them carries your PDF, because the rendering happens in the tab.

Convert the pages with PDF to JPG. To see what a pixel count means in inches or centimetres at a given resolution, the pixel converter works it out for print, and if you want the words rather than pictures of them, PDF to text extracts them.