PDF to JPG in high quality: which DPI to choose

The quick answer

Our PDF to JPG converter has three sharpness settings. Pick by what the picture is for:

Keep the format on JPG unless you have a reason for PNG (see JPG or PNG). If a website or print shop asks for "300 DPI", choose High: it is 300 pixels per inch.

If you only remember one thing: Normal for screens, High for paper and zooming. The rest of this article explains why, so you can decide for yourself when a job doesn't fit the table.

What DPI and PPI mean for a PDF page

A picture is a grid of coloured dots called pixels. A PDF page is different: it has a size on paper, in inches or millimetres, and its text and drawings are stored as shapes, not dots. To turn a page into a picture, a converter has to decide how many pixels to use for each inch of paper. That number is the ppi, pixels per inch.

The sum is simple: page width in inches × ppi = picture width in pixels. An A4 page is 8.27 inches wide, so at 150 ppi it becomes 1240 pixels wide, and at 300 ppi, 2480 pixels.

DPI, dots per inch, is the same idea from the world of printers and scanners. People use the two words for the same thing, and when a form asks for "300 DPI", it means 300 pixels for each inch of the page.

Doubling the ppi gives four times the pixels, because the picture grows in both width and height. That is why High has four times the pixels of Normal, and why its files are much bigger. In our tests, High files were 2.4 to 4.3 times the size of Normal ones.

The ppi travels with the picture. Each JPG or PNG our converter makes carries its ppi inside the file. So when you put it into Word or print it, the picture comes out at the real size of the page, instead of being treated as some default size and printed too big or too small.

Text pages can be drawn at any sharpness. Because text and drawings in a PDF are shapes, they are drawn fresh at whatever ppi you pick, and more ppi really does mean crisper letters. Scans work differently, as the section on scans explains.

Choosing the setting for screens, printing and zooming

For screens: Normal

An A4 page at Normal is 1240 × 1754 pixels. Phone screens and most computer screens show a whole page with fewer pixels than that, so there is room to zoom in a little before letters get soft. For WhatsApp, slides, websites and email, Normal is plenty. Going higher only makes files bigger and slower to send.

For printing: High

Paper shows detail that screens hide. Normal is fine for everyday home printing, but for the sharpest prints, especially of small print, thin lines and fine shading, choose High: 300 ppi is the usual standard for sharp prints. If all you need is a paper copy, though, printing the PDF itself is simpler and sharper still.

For zooming and cropping: High

When someone will zoom far into the picture, or you will cut out part of it, every extra pixel counts. Say you want just the table at the bottom of a report page, or the signature on a letter. Cropped from a High picture, that part keeps four times the pixels it would have at Normal, so it stays sharp when shown on its own.

For small file sizes: Small

Small makes the smallest files, which helps with previews, website thumbnails and forms with a tight size limit. Small print can be hard to read at 72 ppi, so check the result before you use it for anything important.

The page tells you the size before you convert. The line under the choices says how many pixels a page of your PDF will become, for example "An A4 page becomes 1240 × 1754 pixels." Change the setting and it updates, so you can match a size someone asked for.

Scanned PDFs: why higher isn't always sharper

A scanned PDF is a stack of pictures. Each page is a photo that the scanner or phone took at its own resolution, and the detail it caught is all the detail there is.

Pick a higher ppi than the scan has, and the converter makes a bigger picture by stretching the same detail over more pixels. The file grows, and the page looks no sharper. That is why Normal is usually enough for scans.

How to tell if your PDF is a scan: open it and try to select a word. If you can't select any text at all, it is most likely a scan. Zooming far in also shows it: scanned text turns blocky or fuzzy, while real text stays smooth at any zoom.

When High still helps for scans: when the scan itself was made at a high resolution, like an office scanner at 300 dpi, and you want to print it or crop out a small part. Then High keeps the detail the scanner caught instead of throwing some away.

Scans also take longer to convert, because each page is a big photo that has to be unpacked before it can be drawn. Our 42-page scan of 47.8 MB took 11.9 seconds at Normal and 20.0 seconds at High.

JPG or PNG for high quality

JPG is the right choice for almost everything, including high-quality work. JPG saves space by leaving out tiny details the eye hardly notices. We save JPGs at quality 90 out of 100. In our tests on seven kinds of page, from text to photos and scans, that made files 27% smaller than quality 95, and letters stayed as crisp as in a PNG. Lower settings, like 75 or 80, left a faint haze around letters, so we don't use them.

PNG keeps every pixel exactly. Choose it when you will edit the picture further and save it again, when a page is fine line art or a diagram you want pixel-perfect, or when a website asks for PNG. How much it costs depends on the page:

For pages of text, PNG was only 9% to 28% bigger, so if you prefer it, the cost is small. For the scan, PNG was seven times bigger. Rule of thumb: scans and photos as JPG; text and diagrams as either, PNG if you want it exact.

Neither format keeps see-through parts: every page is drawn on white, like paper. The JPG or PNG part of the guide has more.

How big the pictures get: measured examples

We converted these files in Chrome on our test computer. "Pictures, in all" is the total for every page; the time is what the page showed when it finished. Phones usually take longer.

Per page, our sample scan came out at 60 to 70 KB each at Small and 396 to 422 KB each at Normal. Three things stand out:

• High JPG is a few times bigger than Normal: 6.81 MB against 1.58 MB for the sample scan. That is the price of four times the pixels.
• High PNG of a scan is huge: 43.3 MB for four pages. Avoid it unless you truly need every pixel.
• The pictures can be bigger than the PDF. The 14-page paper is 992 KB as a PDF, because its text is stored as shapes, but 7.26 MB as Normal JPGs. A picture of text usually takes far more room than the text itself.

Each picture in the result shows its pixel size and its file size, so you can see what you got before you download anything. The full table, including a 400-page scan, is in the guide's real results.

Posters, drawings and very big pages

A big page at a high ppi makes an enormous picture, and browsers can only draw pictures up to a certain size. Our converter allows one picture up to 40 million pixels on a computer, or 16 million on iPhone and iPad, whose browsers can't draw bigger pictures.

• A2 posters fit at High on a computer.
• Bigger pages, like an A1 poster or a large drawing, are drawn at a lower ppi so that they fit. An A1 page at High comes out at 227 ppi on a computer and 144 ppi on an iPhone.

You won't be caught out: the line under the choices says when a page will be made smaller, and the result says so too. For large drawings and posters, use a computer, which can draw bigger pictures than an iPhone or iPad.

How to check the quality before you use it

1. Look at the numbers in the result. It shows the pixel size, the ppi and the file size, like "1240 × 1754 px · 150 ppi".
2. On a computer, open the picture and zoom to 100%, where one pixel of the picture is one pixel of your screen. On a phone, zoom in as far as you can. Read the smallest print on the page: footnotes, stamps, figures in a table.
3. For printing, check the print preview. Because the picture carries its ppi, choosing actual size (or 100%) should print it at the size of the original page.
4. If text looks soft, convert again at High. If it is still soft, the PDF is probably a scan, and the scan itself is the limit.

Changed your mind about the setting? Just pick another one. The old pictures are cleared and the Convert button comes back, so what you download always matches what you chose.

What it can't do, and what to use instead

• No custom DPI. You choose 72, 150 or 300 ppi, nothing in between and nothing higher. For screens and most printing, 300 is already plenty. Desktop programs such as Adobe Acrobat, and Preview on a Mac, can export a page at a resolution you type.
• No quality slider. JPGs are always saved at quality 90, which in our tests kept letters as crisp as PNG. For pixel-perfect pages, pick PNG.
• No cropping or exact pixel sizes. Each picture is the whole page. To cut out part of it, or to make it an exact width and height that a website demands, convert at High and then crop or resize the picture in your gallery or a photo editor.
• Text becomes part of the picture. A picture keeps how the text looks, not the text itself, so it can't be searched or copied. Keep the PDF too.
• Locked PDFs need their password, typed on the PDF's card. It is used only on your device.

If you need a smaller PDF rather than pictures, you don't need to convert at all: our PDF compressor shrinks PDFs and keeps text sharp, and Resize PDF makes a PDF fit a limit like 100 KB. To save just one page as a picture, for WhatsApp, slides or an upload form, see saving a PDF page as an image.