Scan Resolution and DPI Explained: How Sharp Does a Scan Need to Be?

Resolution decides how much detail a scan holds. Too little and text turns fuzzy; too much and files become huge for no benefit. Understanding a few numbers helps you choose.

What DPI means

DPI stands for dots per inch. It describes how many pixels a scanner captures across each inch of the original. A page scanned at 300 DPI has 300 pixels for every inch, so an A4 page (about 8.3 × 11.7 inches) comes to roughly 2480 × 3508 pixels.

Phone scans and DPI

A phone doesn't scan in the way a flatbed does. It photographs the page, so the effective DPI depends on the camera's pixel count and how much of the frame the page fills. That's why filling the frame matters: a page that occupies only half the picture gives you half the detail.

Rough guidelines

• About 150 DPI: enough for casual reading on a screen and for simple email attachments.
• About 200 DPI: comfortable for most everyday documents on screen.
• About 300 DPI: the common standard for documents intended for printing, archiving or later text recognition.
• About 600 DPI: for fine print, small photographs or detailed line work.

Most modern phone cameras can exceed 300 DPI for an A4 page if you fill the frame.

How resolution affects file size

Doubling the DPI quadruples the number of pixels. A high-resolution colour scan of a multi-page document can run to tens of megabytes. Compression reduces this, but very high resolution is rarely needed for ordinary paperwork.

Match resolution to purpose

• Email and online forms: moderate resolution, compressed.
• Official submissions: follow the stated size and quality requirements.
• Archiving important documents: higher quality, kept as a master copy.
• Photos and artwork: higher resolution in colour.
• Receipts: moderate is enough, so long as numbers stay legible.

Keep a master, share a smaller copy

For important documents, keep a high-quality master file, and create a compressed copy for sharing. This gives you the best of both.

Small text

Small print, such as terms and conditions, tests resolution the most. Zoom in on the smallest text after scanning. If it's hard to read on screen, it'll be hard to read on paper.

More isn't always better

Beyond a certain point, extra resolution captures paper texture and noise, not useful detail. Choose the lowest resolution that keeps the text comfortably clear.

Checklist

1. Page fills the frame.
2. Text sharp at 100 percent zoom.
3. Resolution appropriate to purpose.
4. Master copy saved for important items.
5. Compressed copy created for sharing.

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