PDF to JPG at high resolution: which DPI to choose

Turning a PDF page into an image means choosing a resolution, usually expressed in DPI. Pick too low and text goes fuzzy on a big screen or in print; pick too high and you get enormous files that are slow to share and may not even render on a phone. This guide explains what DPI means for a PDF, gives exact pixel sizes for common page sizes, and shows which setting suits which job, including the cases where a higher number adds nothing at all.

What DPI means when you convert a PDF

PDF pages don’t have pixels. Their size is defined in points, where 72 points make one inch, and most of their content (typed text, lines, charts) is stored as shapes that can be drawn at any size. A pixel image only appears when you render the page, and DPI (dots per inch, often used interchangeably with PPI, pixels per inch) decides how many pixels each inch of the page becomes.

The arithmetic is simple: pixels = page size in inches × DPI. An A4 page is about 8.27 × 11.69 inches, so at 150 dpi it becomes about 1240 × 1754 pixels. Double the DPI and both dimensions double, which means four times as many pixels. That’s why file sizes climb so quickly at high settings.

Pixel sizes for A4 and US Letter

These are the dimensions PDF to JPG produces for a standard portrait page at each resolution (rounded to the nearest pixel, as the tool does). Megapixels are for the A4 size.

The tool offers 72, 150 and 300 dpi as presets and accepts any whole number from 36 to 600 dpi as a custom value. Before you convert, it shows the pixel size the first page will come out at, so you can check the numbers against whatever you’re preparing the image for.

Which DPI to choose for each job

• A preview or thumbnail (a website listing, a file picker): 72 dpi is plenty and keeps files tiny.
• A slide, a document or an email: 150 dpi. Text is crisp on ordinary screens and in a slide deck, and files stay manageable. It’s the default for that reason.
• Social media or a website hero image: start at 150 dpi and check the pixel width against the size the platform or page actually displays; platforms resize uploads, and their recommended sizes change, so check their current guidance.
• Print: 300 dpi for a page printed at its original size. If you’ll print it smaller, you can go lower; if you’ll blow part of it up, go higher.
• Inspecting detail in an architectural drawing, a map or a dense chart: 300–600 dpi, keeping in mind the device limits below.

A useful rule of thumb is to work backwards from the pixels you need. If an image will be shown 1200 pixels wide and the page is 8.27 inches wide, 1200 ÷ 8.27 ≈ 145, so 150 dpi is right and 300 dpi would just waste space.

When a higher DPI adds nothing

Raising the DPI only adds detail that the PDF actually contains. Text and vector graphics are redrawn from their shapes at every resolution, so they genuinely get sharper at 300 or 600 dpi. Photos and scans embedded in the page are different: they already have a fixed number of pixels.

Suppose a page is a document scanned at 200 dpi. Rendering it at 600 dpi produces an image with nine times as many pixels as at 200 dpi, but those extra pixels are interpolated from the 200 dpi original. The result looks no sharper; it’s just bigger. For scanned PDFs, a DPI close to the original scan resolution (often 200 or 300) is the sweet spot. If you don’t know it, compare 150 and 300 dpi on one page and zoom in: if the 300 dpi version isn’t visibly better, use 150.

JPG or PNG?

JPG artefacts are most visible around sharp edges, which is exactly what text is made of. If a text-heavy page looks slightly smudged at 90% quality, either raise the quality or switch to PNG. For a page that is mostly a photograph, JPG at 85–90% is hard to tell apart from the original and much smaller.

The Transparent background option (PNG only) leaves unpainted parts of the page clear instead of white, handy for a logo or a signature drawn on an otherwise blank PDF page that you want to place over another design.

Very large pages, phones and device limits

Browsers cap the size of a single image they can draw. On iPhones and iPads the limit is 16,777,216 pixels (4096 × 4096), and PDF to JPG applies the same cap on other phones and tablets. On computers the tool allows up to about 50 megapixels per page, because larger images get slow and memory-hungry.

In practice: an A4 page at 600 dpi (34.8 megapixels) converts fine on a computer, but on a phone it’s reduced to roughly 415 dpi so it fits. An A3 page at 600 dpi (about 70 megapixels) is reduced to roughly 500 dpi even on a computer. When this happens, the tool lowers the resolution for that page only and tells you which page and what DPI it received, both before you convert and in the result. If you need the full resolution for a poster-sized page, convert it on a computer, or pick a DPI just under the limit.

Step by step: convert at the right resolution

1. Open PDF to JPG and choose your PDF. It’s rendered in your browser and never uploaded.
2. Pick All pages, or Choose pages and tap the ones you want (or type a range such as 1-3, 5).
3. Choose JPG or PNG. For JPG, set the quality; for PNG, decide whether you want a transparent background.
4. Choose 72, 150 or 300 dpi, or a custom value. Check the pixel size shown underneath.
5. Convert. One page downloads as a single image; several download as a ZIP, with files named like report-p001.jpg so they sort in page order.

Going the other way? JPG to PDF turns images back into a document. And if your real goal is a smaller PDF rather than images, use Compress PDF instead: converting pages to pictures makes text unsearchable, while compression keeps it as real text.