RapidHow to Reduce Scanned PDF Size — Smaller Scans, Same Pages
Why a few scanned pages can be bigger than a 100-page report, and three ways to make a scanned PDF smaller.
⚠️ Always use a copy of your document, never the original. Keep your original file safe.
How to reduce scanned PDF size starts with knowing why scans are big. A scanner saves every page as a picture, blank white space included, so one scanned page is about 0.5 MB at 300 DPI in color — about 10 times a page of plain text — and a higher resolution (DPI) makes it bigger. To make a scanned PDF smaller, scan text documents in black and white, which was about 90 percent smaller than color in our tests, at about 150 to 300 DPI, then compress the PDF: in our tests, a scanned PDF became 54 to 92 percent smaller, depending on the level. If it is still too big, remove the pages you do not need.
This guide is only about scanned PDFs. For PDFs made from Word, Google Docs or other programs, see how to compress a PDF and how to compress a PDF without losing quality.
Why Scanned PDFs Are So Big
A PDF made from a document stores the letters and the font, which takes very little space. A scanned PDF stores a picture of each page. The picture records every dot on the page — the white margins and the gaps between lines take up as much room as the text. These are the typical sizes per page used by the PDF File Size Calculator and how many pages is 1MB PDF, at medium quality (for scans, a typical 300 DPI color scan):
| Kind of page | Typical size per page | Pages in 1 MB |
|---|---|---|
| Plain text | About 0.05 MB | About 20 |
| Text with images or charts | About 0.2 MB | About 5 |
| Image-heavy | About 0.5 MB | About 2 |
| Scanned (300 DPI, color) | About 0.5 MB | About 2 |
Two settings make a scan even bigger:
- Color. A color scan stores three color values for every dot, grayscale stores one, and black and white stores only on or off. In a PDF, color and grayscale end up close in size, because JPEG compression already stores color detail at a lower resolution. Black and white is much smaller.
- Resolution (DPI). DPI is the number of dots per inch. Doubling the DPI makes four times as many dots: a letter-size page at 300 DPI is 2,550 × 3,300 dots, and at 600 DPI it is 5,100 × 6,600 dots.
Fix 1: Change Your Scan Settings (Before You Scan)
This makes the biggest difference, because a smaller picture starts out smaller. These are typical sizes per page by resolution and color mode, the same as the scan size table in the PDF File Size Calculator:
| DPI | Color | Grayscale | Black and white |
|---|---|---|---|
| 150 | 150–300 KB | 150–300 KB | About 20 KB |
| 200 | 200–450 KB | 200–450 KB | About 25 KB |
| 300 | 350–650 KB | 350–600 KB | 30–150 KB |
| 600 | 0.9–1.7 MB | 0.8–1.9 MB | 50–500 KB |
Sizes are for one letter-size page saved as a PDF, from our own test scans of a letter with text and a small photo and from the file sizes ScanSnap publishes for its scanners. Real scanners vary with the page, the scanner and its compression setting. ScanSnap scans black and white at a higher DPI than color, which is why the top of the black and white range is larger than our own results. Scan figures last reviewed October 2026.
- Scan text documents in black and white. This is the biggest saving: in our tests, a black and white scan was about 90 percent smaller than the same page in color. Use color only when it matters, such as for a colored stamp or a photo. Grayscale saves only about 10 percent compared with color, so it is not worth choosing just to save space.
- Lower the resolution. 150 DPI is enough to read most text documents, and a 150 DPI scan is about 40 percent of the size of a 300 DPI scan. Many scanners default to 300 DPI or more, which makes each page bigger than it needs to be. To see the pixel size of a page at any DPI, use the PDF Resolution Calculator.
- Crop the empty space if your scanner or app offers it, and scan only the pages you need.
- On a phone scanning app, choose a document or black-and-white mode rather than a color photo.
Planning to scan a large batch? The Scanning Time Calculator estimates how long the job will take.
Fix 2: Compress the Scanned PDF (After You Scan)
If you already have the scan, compress it with Compress PDF. It redraws the images in your PDF at a lower resolution and saves them as JPEG pictures, all in your browser. A scanned page is one big picture, so scans shrink well. These are real results from one scanned test PDF of 8.77 MB:
| Level | Smaller by | About |
|---|---|---|
| High Quality | 54 percent | 4 MB |
| Medium | 78 percent | 1.95 MB |
| Maximum | 92 percent | 0.7 MB |
These are typical results, and your files will be different. Start with High Quality and only try Medium or Maximum if the file is still too big.
Need an exact size, such as 2 MB? See how to compress a PDF to a specific size. For immigration uploads, see IRCC and USCIS PDF file size limits.
Fix 3: Remove Pages You Do Not Need
Every scanned page adds about 0.5 MB in color at 300 DPI, so fewer pages make a smaller file. Blank backs of pages, duplicate scans and cover sheets are common extras. Open Split PDF, type the pages you want to keep (for example 1-4, 6-10) and click Extract Pages. You can also make several smaller files, one for each part, if the place you are sending to accepts more than one file.
What Compression Cannot Do
Compressing a scan keeps every page as a picture. It does not turn the picture into real text, so you still cannot search or copy the text. Making scanned text searchable is called OCR (optical character recognition), and RapidTools does not offer it. Many scanner apps can add OCR when you scan.
Frequently Asked Questions
Why is my scanned PDF so big?
A scanner saves every page as a picture, including the blank white space, so one scanned page is about 0.5 MB at 300 DPI in color — about 10 times a page of plain text. A higher resolution (DPI) makes each page bigger, and scanning in black and white makes it much smaller.
What DPI should I use to scan documents?
For text documents, 150 DPI is usually enough and gives about 150 to 300 KB per page in color, or about 20 KB in black and white. Use 200 DPI for documents with photos, and 300 DPI or more only for printing or long-term archiving, because each page gets bigger: a 600 DPI scan is about 5 to 8 times the size of a 150 DPI scan.
Does scanning in grayscale make the PDF smaller?
Only a little. In our tests and in the sizes ScanSnap publishes, a grayscale scan was only about 10 percent smaller than the same page in color, because PDF compression already stores color detail at a lower resolution. Black and white is the big saving: for text documents it was about 90 percent smaller than color in our tests.
How much smaller can compression make a scanned PDF?
In our tests, a scanned PDF of 8.77 MB became about 54 percent smaller on High Quality, 78 percent smaller on Medium and 92 percent smaller on Maximum. These are typical results, and your files will be different. Check that small text is still easy to read.
Can RapidTools make the text in my scan searchable?
No. Making scanned text searchable is called OCR, and RapidTools does not do it. Compressing a scan keeps each page as a picture, so the text stays a picture too.