Resolution: 96, 150 or 300 dpi, and large pages
A PDF page is described in physical units — inches or millimetres — not in pixels. To become a JPG or PNG, the page is drawn onto a grid of pixels, and the dpi setting decides how fine that grid is.
What dpi decides
dpi (dots per inch) sets how many pixels each inch of the page gets. An A4 page is 8.27 inches wide, so at 150 dpi it becomes about 1240 pixels wide. Double the dpi and you get twice as many pixels across and four times as many in total.
| Page | Compact · 96 dpi | Standard · 150 dpi | High · 300 dpi |
|---|---|---|---|
| A4 | 793 × 1123 px | 1240 × 1754 px | 2479 × 3508 px |
| US Letter | 816 × 1056 px | 1275 × 1650 px | 2550 × 3300 px |
You do not need to calculate this: in the settings, Compact, Standard and High each show the pixel size of your own first selected page before you save. The pixel size is the same for JPG and PNG; only the file size differs.
A starting point for each use
| You want to… | Start with |
|---|---|
| show the page on a screen, in a slide or a chat | 96 or 150 |
| keep a readable copy of a text page | 150 (the default) |
| zoom into small print, thin lines or a diagram | 300 |
| print the image at the page’s original size | 300 |
If text looks soft when you zoom in, go up a step; if the file is larger than you need, go down one.
How resolution changes file size
Four times the pixels does not mean exactly four times the file, but it is the main driver. In our tests on an A4 test page with a full-page photograph, going from 150 to 300 dpi took the JPG from 0.25 to 0.85 MB and the PNG from 4.0 to 13.2 MB (Chromium). With PNG at High, the settings add a reminder that files can get very large; it does not stop you. JPG or PNG has the full table for both browsers.
More dpi does not add detail
A higher dpi draws what the PDF describes more finely. Text, lines and vector drawings benefit, because the PDF describes them precisely. A photo or a scan inside the PDF only has the detail it was embedded with: a page scanned at 100 dpi does not become sharper when it is drawn at 300 dpi. You get more pixels, not more information.
When large pages are scaled down
To keep memory in check, a single image is limited to 8192 pixels on its longest side and 24 megapixels in total. The page’s shape alone does not decide whether a page reaches this limit — its physical size and the dpi decide it together.
A4 and A2 have exactly the same proportions. At 300 dpi, A4 becomes 2479 × 3508 px (about 8.7 megapixels) and stays well inside the limit. A2 would be about 4961 × 7016 px (about 35 megapixels); it is scaled down, proportions kept, to about 4119 × 5826 px — roughly 249 dpi. At 150 dpi the same A2 page fits without any change.
Very wide or very tall pages reach the side limit instead. Our wide test page (2380 × 595 pt, about 84 × 21 cm) became 8192 × 2048 px at 300 dpi instead of 9917 × 2479, and the tall page with the same size turned on its side became exactly the mirror image, 2048 × 8192 px.
Before you save, a note under the page selection tells you when a selected page will be scaled down and names the lowest resolution that will actually be used. The settings show the same note next to the pixel size. Nothing is cut off: the whole page is in the image, just with fewer pixels than the dpi you chose would give.
Convert your pages in the browser → PDF to Image