To reduce scanned document file size, scan text at 200 to 300 dpi in black and white or grayscale, and shrink what you already have with a PDF compressor. A scan is a stack of photographs, so resolution and color mode decide almost everything. Here are the limits you hit, and the Smol setting for each.
| What you are sending | The limit you hit | The Smol setting |
|---|---|---|
| A multipage scan to email | Gmail: 25 MB for personal accounts. Email encoding adds about 37% | PDF preset Small or Medium, then check the size |
| A scan that must stay searchable | OCR needs enough pixels per letter; our test fell apart near 55 PPI | OCR first in another tool, then Medium (or Small) |
| A scan for an archive or a print | Your rule may ask for 300 dpi, and Smol presets are pixel caps, not dpi | Large or Original, or skip compression |
| A whole folder from the copier | Dozens of files, each over a form or portal limit | Drop the folder in; one preset for all |
Why is a multipage scan too large?
A scanned PDF is a photograph of each page, not text, so every sheet stores millions of pixels. A multipage scan multiplies that by the page count, which is why a scanned packet grows so quickly.
We built the same three-page agreement twice for our scanned PDF test. As a text PDF with embedded fonts it was 87,788 bytes. As a 300 PPI color scan of the same pages it was 5,017,560 bytes, about 57 times larger, and it contained no searchable text. Three pages at that size means a 30-page packet lands near 50 MB, which is more than Gmail’s limit allows.
Three things drive the size: resolution, color mode, and the compression your scanner applies when it writes the PDF. You control all three at the scanner, and you can shrink the result afterward on your Mac.
What scanner dpi settings work for documents?
For text documents, 200 to 300 dpi. Epson’s guidelines list 200 to 300 dpi for printing, faxing, OCR or a text-searchable PDF, and 96 to 150 dpi for email or screen viewing only. Toshiba says 200 × 200 dpi is sufficiently legible for normal text.
| Purpose | Resolution | What the maker says | Source |
|---|---|---|---|
| Email or screen viewing | 96 to 150 dpi | Epson’s range for email, screen viewing or web posting | Epson, read 11 October 2026 |
| OCR, print or a searchable PDF | 200 to 300 dpi | Epson’s range; “Larger file sizes” is listed as the cost of higher resolution | Epson, read 11 October 2026 |
| Everyday text pages | 200 dpi | “200 × 200 dpi produces an image that is sufficiently legible” | Toshiba, read 11 October 2026 |
| Any setting | Higher dpi | “The higher the DPI the clearer the image will be, however the scan time and document size will increase” | Brother, read 11 October 2026 |
Our own measurement agrees on where the floor is. An OCR engine recovered every word of our test page at 109 PPI, 96.8% at 82 PPI, and 1.42% at 55 PPI (Tesseract, one test document). Pick 200 dpi if size matters and 300 dpi if you may OCR or print the scan later.
Which color mode makes the smallest scan?
Black and white for black text on white paper, grayscale for pages with stamps, shading or photos, color only when color carries meaning. ScanSnap’s help page says black-and-white scans are saved only as PDF with a fixed compression rate. Brother describes a similar lever in its File Size slider.
In our test, converting the scan to grayscale in Ghostscript, a separate free tool, cut it by 65.7% with the resolution untouched. Smol itself has no grayscale option, so set the mode at the scanner.
How big should a scan to PDF file be, and where does it get stuck?
Small enough for the strictest place it has to go. Email is usually the tightest, so work backward from the recipient’s cap and the roughly 37% that email encoding adds.
| Where it goes | Limit | What happens above it | Source |
|---|---|---|---|
| Gmail (personal accounts) | 25 MB | Gmail removes the files and inserts a Google Drive link | Gmail Help, read 11 October 2026 |
| Outlook, Outlook for Mac (Exchange Online) | 150 MB file attachment size limit | Some email clients may have lower limits; administrators can set a custom message limit | Microsoft Learn, read 11 October 2026 |
| Outlook for iOS and Android (Exchange Online) | 33 MB message size limit | Message size limit; some email clients set lower limits | Microsoft Learn, read 11 October 2026 |
The recipient’s server counts too, and you rarely know its cap. Our PDF email guide measured encoding at 36.8%, so a 25 MB cap means aiming at about 18 MB, and an unknown recipient means closer to 7 MB. For forms and portals, see PDFs that are too big to upload.
How big is a searchable PDF, and does compressing break it?
The text layer is tiny, and compressing with Smol did not remove it in our test. In the scanned PDF test, adding a text layer cost 17,753 bytes for three pages at the Tiny preset, under 6 KB a page. Every Smol preset kept all 1,405 searchable words.
Order matters. Smol does not run OCR, and no compression setting adds a text layer, so use your scanner’s searchable-PDF option or another OCR tool first, at full resolution. Compress after, never before: a scan squeezed to 55 PPI gave the OCR engine almost nothing to read.
Which Smol PDF preset should I use for scans?
Medium for most office scans, Small when the file must be email-sized, Large or Original when someone will print it. Presets are long-edge pixel caps, not dpi targets, so effective PPI depends on page size.
| Preset | Pixel cap, long edge | Effective PPI on Letter | Size of test scan | Words findable |
|---|---|---|---|---|
| Source (OCR, uncompressed) | 3,300 px | 300 | 5,032,225 B | 1,405 |
| Original | 2,400 px | 218 | 1,736,280 B | 1,405 |
| Large | 1,800 px | 164 | 624,925 B | 1,405 |
| Medium | 1,200 px | 109 | 284,590 B | 1,405 |
| Small | 900 px | 82 | 166,998 B | 1,405 |
| Tiny | 600 px | 55 | 65,126 B | 1,405 |
These sizes come from one test scan (26 September 2026, Smol 1.0.35), and the OCR layer was added by a separate tool. Your pages will land elsewhere, so check the result. Note that Original is not lossless: it re-encodes and resamples above 2,400 px. Presets are saved on each Mac, so write down the one your office uses and recreate it on the others. The full ladder is in what the presets actually do.
How do I shrink a folder of scans at once?
Copy the folder from the shared drive, drop it into Smol, choose one preset, run it. The copies appear beside the originals with a _compressed suffix.
Scan at the right settings
Black and white or grayscale, 200 to 300 dpi, and the searchable-PDF option if you need one.
Copy the scans to your Mac
Smol writes copies and does not overwrite originals by default.
Drag the folder into Smol and choose Medium
Use Small if the files must go by email. Mixed files can go in together.
Read the per-file sizes
Find the largest output. If it clears your cap with the email overhead, they all do.
Search one file and attach the copies
Press Command-F on one output. If a visible word is found, send the compressed copies.
For a standing hot folder, batching 100 PDFs covers the drop. Watched folders can enlarge files that are already optimized, so use them only for fresh scanner output.
How do offices reduce scanned document file size today?
Scanner settings first, because they cost nothing and fix the file at the source. Compression afterward is for files already scanned.
| Option | Cost | Good at | Watch for |
|---|---|---|---|
| Scanner or copier settings | Free | Black and white, 200 dpi and compression levels: ScanSnap has levels 1 to 5, Brother a Small to Large slider | Menus vary by model; it does not help scans already made |
| Preview, Reduce File Size | Free, built in | A quick shrink for one file | Removed the text layer in our test and can enlarge text PDFs |
| OCRmyPDF | Free | Adds a text layer; its defaults made our test file 45.1% smaller | Terminal tool; 300 PPI stays |
| Smol | $29 once | A folder of PDFs at one preset, on your Mac | No OCR, no grayscale, presets are pixel caps |
For other tools, see the Mac PDF compressor comparison.
When Smol is the wrong tool for scanned documents
- You need a text layer. Smol does not run OCR. Use the scanner’s searchable-PDF option or an OCR tool first.
- A rule requires exactly 300 dpi. Smol presets are pixel caps, not dpi targets, so skip compression or fix it at the scanner. See compressing a PDF for print.
- It is one receipt, once. Re-scan at 200 dpi in black and white or use the scanner’s file-size setting instead.
- You need to merge, split, sign or redact. Smol does none of these.
Law firms and accountants scanning client files should also read our guides for law firms and accountants. Offices with several Macs: Solo is one Mac, Team is $49 for three, and Enterprise is $20 a seat for 5 to 500. See pricing.
Frequently asked questions
How do I reduce scanned document file size?
Scan text in black and white or grayscale at 200 to 300 dpi, and turn on your scanner’s file-size or compression setting. For scans you already have, drop them in Smol and choose Medium or Small. Check one output: search a word and confirm the size clears your limit with email overhead.
What scanner dpi settings work for documents?
Epson lists 200 to 300 dpi for printing, faxing, OCR or a searchable PDF, and 96 to 150 dpi for email or screen viewing. Toshiba calls 200 dpi sufficiently legible for normal text. Use 300 dpi if you may OCR or print the scan later, 200 dpi if size matters.
Why is my multipage scan too large to email?
Each page is a photograph, so size grows with every sheet. Our three-page 300 PPI color test scan was 5,017,560 bytes, and email encoding adds about 37%. Gmail personal accounts stop at 25 MB, so a long packet needs lower dpi, black and white, or a Smol preset.
How does scan to PDF file size change with color mode?
Black and white is smallest, grayscale is next, color is largest. Brother says higher color quality makes scans slower and larger. ScanSnap saves black-and-white scans only as PDF with a fixed compression rate. In our test, grayscale alone cut the scan by 65.7% at 300 PPI.
How big is a searchable PDF?
Slightly bigger than the same scan without a text layer. In our test the layer added 17,753 bytes for three pages, under 6 KB a page. The picture dominates. Add OCR first, then compress; in our test all 1,405 words stayed searchable at every Smol preset.
Does Smol run OCR on scanned documents?
No. Smol compresses scanned PDFs but does not add a text layer, and no preset can create one. If the text must be searchable, run OCR first with your scanner software or another tool, then compress the result and press Command-F on one output to confirm.
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