What DPI and pixels really mean, how many pixels an A4 page needs for reading, OCR and printing, and how to choose a resolution without making files huge.
“What resolution should I scan at?” is a question with a short, practical answer once you see how pixels, inches and file size connect. This guide gives you the numbers for an A4 page, explains why a bigger picture is not always a better one, and shows how to pick a sensible setting for reading, text recognition and printing.
A digital picture is a grid of pixels, for example 3000 by 4000. That grid is the only thing that determines how much detail the picture holds. DPI or PPI (dots or pixels per inch) is simply the pixel count divided by the physical size at which the picture is shown or printed. If an A4 page, which is about 8.27 by 11.69 inches, is stored as 2480 by 3508 pixels, then it is about 300 pixels per inch.
So “300 DPI” without a size means nothing. The same pixel grid is 300 DPI when printed small and 75 DPI when stretched four times larger. When you want to know whether a picture is sharp enough, ask how many pixels it has and how large you want it to appear.
For US Letter paper (8.5 × 11 inches), 300 DPI is 2550 × 3300 pixels.
A typical 12-megapixel phone picture measures about 4000 by 3000 pixels. If you photograph an A4 page so that its long side fills the 4000-pixel direction, you have roughly 340 pixels per inch, already above 300 DPI. Higher-resolution phone cameras give even more. This is why a careful phone photo can match a desktop scanner, and why cropping tightly and holding the phone close matters more than any setting: pixels spent on the table beside the page are wasted. See how to scan a document with your phone camera.
Around 100 to 150 pixels per inch at page size is enough. The text is clear when you zoom in a little, and files stay small. This is the right target for forms, receipts and attachments.
Text recognition needs the letters to be clearly shaped. About 300 DPI at the printed size is the common recommendation for body text of 10 to 12 points. Smaller type or poor contrast needs more. If a scan will be read by OCR, keep a higher-quality copy separate from the small copy you send out. The guide on how OCR works and why it makes mistakes explains why.
300 DPI gives crisp text. 200 DPI is acceptable for ordinary documents read at normal distance. Below about 150 DPI, the edges of letters start to look soft on paper.
300 DPI is the standard for prints that will be held in the hand. Larger prints that are viewed from further away, such as a poster, can look fine at lower values, because the eye cannot resolve the fine detail at a distance.
Pixel count and file size rise together. Going from 150 to 300 DPI quadruples the number of pixels, since both width and height double. A page that is 250 KB at one setting can be well over 1 MB at the next. For documents that you will email or upload, take only as many pixels as the purpose needs.
In Image to PDF, the three file size modes do this for you. Small File keeps pages light for WhatsApp and email, Balanced suits reading and printing, and High Quality keeps the most detail. The tool shows an estimated total size before you generate. If the result is still too large, see how to make a PDF smaller.
When you convert PDF pages to images with PDF to Image, you choose a render resolution: Standard, High or Ultra High. Standard is fast and makes smaller images, High is a good default, and Ultra High is for fine print and charts you plan to zoom into. Choose Ultra only when needed, since the files are large and a long document takes longer to render on a phone. Choose JPG for small files and PNG for the sharpest text, as explained in JPG vs PNG vs PDF.
Take the picture sharp and well lit, at a pixel size that gives about 300 pixels per inch at the paper size. Keep that as your master. Then make smaller copies for email, forms and messaging, and larger prints from the master when needed. Everything in Docsworker runs in your browser, so your originals are not uploaded.
PPI (pixels per inch) describes how many pixels of a picture fit into one inch on a screen or page. DPI (dots per inch) strictly describes the dots a printer puts down. In everyday use people say DPI for both.
No. The sharpness is set by the number of pixels in the picture. A DPI label in the file only tells software how large to print it. Enlarging a small picture adds no new detail.
About 300 DPI at the printed size is a commonly recommended level for ordinary 10 to 12 point text. A sharp phone photo of a full A4 page is usually above that.
Because the pictures contain more pixels than you need. Reducing the pixel count to what the job requires is what makes the file smaller.