What DPI Should You Scan Documents At? 150, 300, or 600
DPI means dots per inch, the number of samples a scanner takes across each inch of paper. Doubling it quadruples the data, because the increase applies in both dimensions. A page at 150 DPI might be 300 KB, the same page at 300 DPI around 1.2 MB, and at 600 DPI close to 5 MB. This is why a stack of receipts scanned at maximum quality can produce a folder larger than a video file, and why picking the number deliberately matters more than most people assume.
150 DPI is adequate when the scan exists only so a human can read it on a screen. Delivery notes, meeting handouts, product manuals you want to keep for reference, or a page you are emailing to a colleague all work fine here. Text at normal body size remains legible, files stay small enough to attach without compression, and pages load instantly on a phone. What 150 DPI cannot do reliably is feed OCR or survive being printed again, because fine detail in the letterforms is simply not captured.
300 DPI is the working standard and the right default for almost everything you intend to keep. It is the resolution at which OCR engines perform best, because character strokes are resolved cleanly enough for shape recognition without the noise that very high resolutions introduce. It is also the traditional threshold for acceptable print reproduction. Contracts, tax records, medical documents, certificates, and anything going into long-term archives should be scanned at 300 DPI unless you have a specific reason to go higher.
600 DPI is a specialist setting, not a safer version of 300. It earns its cost when the source has genuinely fine detail: engineering drawings with hairline rules, old documents with faded or tiny print, handwritten annotations you need to examine closely, photographs you intend to enlarge, or anything destined for commercial reprinting. For ordinary printed text it mostly captures paper texture and scanner noise, which inflates the file and can actually reduce OCR accuracy rather than improve it.
Two settings beyond resolution matter just as much. Choose greyscale or colour for anything with stamps, signatures, or highlighting, and reserve pure black and white for clean typed text where it dramatically shrinks the file. Second, scan once at the right resolution rather than rescanning later, since detail not captured cannot be restored. Afterwards you can compress the result, convert PDF to Image or Image to PDF, crop away scanner borders, apply grayscale, and run OCR to make the text searchable, all locally on PdfWill without uploading the documents anywhere.