What resolution to scan at: a practical DPI guide for documents, receipts and photos
October 31, 2026 · 5 min read
"Scan at 300 DPI" is one of those instructions everyone repeats and few people explain. Sometimes it's the right answer. Often it's more than you need, and the result is a file too large to email or upload. And when you're scanning with a phone camera, there's no DPI setting at all — so what does the advice even mean?
This guide explains DPI in practical terms and gives you a starting point for the kinds of documents people scan most often.
What DPI means
DPI stands for dots per inch. For scanning, it really means pixels per inch of the original paper. A letter-size page is 8.5 × 11 inches. Scan it at 200 DPI and the image is:
- 8.5 × 200 = 1,700 pixels wide
- 11 × 200 = 2,200 pixels tall
At 300 DPI, the same page is 2,550 × 3,300 pixels — more than twice as many pixels as 200 DPI, because both width and height grow. At 600 DPI it's 5,100 × 6,600 — four times as many pixels as 300 DPI.
More pixels mean finer detail can be captured, but also a larger file. The question is always: how much detail does this document actually need?
How this applies to a phone scan
Your phone doesn't ask for DPI, but the same math applies. If your camera captures a page at 3,000 pixels wide and the page is 8.5 inches wide, you've scanned at roughly 350 DPI — assuming the page fills the width of the frame.
That last part matters. If the page only fills half of the frame because you were standing back, you've captured it at half the resolution. That's why getting the page to fill most of the frame — while keeping all four edges visible — produces sharper scans than shooting from across the table.
Recommended resolution by use
| What you're scanning | Good target | Why |
|---|---|---|
| Typed letters, invoices, forms for email or portals | 150–200 DPI | Text is clearly readable on screen; files stay small |
| Signed paperwork (BOLs, PODs, contracts) | 200 DPI | Keeps signatures and handwriting legible |
| Small print, receipts, thermal slips | 200–300 DPI | Tiny fonts and faint print need more detail |
| Documents you'll run OCR on | 300 DPI | Text recognition is more accurate with clear, well-resolved characters |
| Documents someone will print and file | 200–300 DPI | Prints look like originals |
| ID cards (licenses, medical cards) | 300 DPI or more | The card is small, so you need more pixels per inch to read the fine print |
| Photographs and artwork you want to preserve | 300–600 DPI | Detail and color matter, and you may want to enlarge later |
For most paperwork, the sweet spot is 200 DPI. Above 300 DPI, text documents rarely get any easier to read; they just get bigger.
Resolution isn't the only thing that matters
A blurry or dark scan at 600 DPI is worse than a sharp, well-lit one at 200. Before you worry about resolution, get these right:
- Focus. Tap the page on screen to focus, and hold still.
- Light. Even, bright, from the side or a window. No shadows across the text.
- Flatness. Curled or folded pages blur at the edges.
- Angle. Straight above the page. Automatic straightening can correct a tilted shot, but a severe angle still stretches the far side of the page.
- Color mode. Black-and-white is right for most typed paperwork and makes much smaller files. Grayscale for pencil and faint text. Color only when color carries meaning.
Color mode often affects file size more than resolution. A black-and-white page at 300 DPI can be smaller than a color page at 150 DPI.
Resolution and file size together
If you need a small file, you have two levers: fewer pixels, or more efficient storage of those pixels. Compressing a PDF to a target size usually reduces image resolution and increases compression until the file fits. That's why starting with a sensible resolution and a black-and-white filter gives you more room — the compression has less to throw away.
A practical approach for most people:
- Scan with the page filling most of the frame, in good light.
- Pick the right color mode: black-and-white for most documents.
- If the file is too large for where it's going, compress it to the size you need.
- Zoom in on the smallest text and any signature to confirm they're still clear.
Example
A bookkeeper scans a month of vendor invoices for a client's records. Typed invoices are scanned in black and white with the page filling the frame. Thermal receipts are scanned in grayscale, close up, so the small print is well resolved. The invoices will be searched later, so the combined PDF is run through OCR. The final file is readable, searchable and small enough to email to the client — without anyone touching a DPI setting.
Common mistakes
- Scanning everything at 600 DPI "just in case." The files become too large to send and aren't easier to read.
- Scanning ID cards from far away. A small card in the middle of a large frame ends up low-resolution. Move closer.
- Assuming higher resolution fixes blur. It doesn't. Retake blurry scans.
- Using color for black-and-white documents. It multiplies file size for no benefit.
- Compressing too far. If small text becomes jagged or blurry, compress to a larger target.
FAQ
Is 300 DPI always the best choice?
It's a safe choice for small print, OCR and documents that will be printed. For everyday paperwork that's read on a screen, 200 DPI is usually enough and produces smaller files.
What resolution do I need for OCR?
Around 300 DPI with good contrast gives OCR the best chance on typical body text. Very small fonts benefit from more. Clean, straight, evenly lit pages matter as much as resolution.
Why does my phone scan look sharper than my office scanner's?
Phone cameras capture a lot of pixels, and if your office scanner is set to a low resolution or a heavily compressed mode, the phone scan can easily look better. It's about the settings, not the device.
Can I increase the resolution of an existing scan?
Not meaningfully. Upscaling adds pixels but not real detail. If a scan is too low-resolution to read, rescan the original.
What does the upload portal mean by "minimum 200 DPI"?
It means the page image should have enough pixels to equal at least 200 per inch of the original paper. A clear phone scan with the page filling the frame normally meets this.