A single scanned page can be 10 MB or more, which makes a 20-page document impossible to email. The good news is that scans are very compressible, if you change the right things.
Why scans are so big
Scanners often default to high resolution, such as 600 DPI, in full color and save as uncompressed or lightly compressed files. A letter-size page at 600 DPI in color is around 5,000 x 6,600 pixels. That’s far more than you need to read text on a screen. For the basics of resolution, see DPI vs PPI.
Step 1: Lower the scan resolution
For readable text documents, 150 to 200 DPI is usually enough to view on screen. 300 DPI is a common standard for archiving and for OCR (turning scanned text into editable text). Going higher mostly adds file size without improving legibility. If you can, change this setting before scanning. If you already have the big scan, resize the image to match.
Step 2: Choose the right color mode
- Black and white (1-bit): the smallest option for plain text pages, but fine details and shading are lost.
- Grayscale: a good middle ground for text with some shading. Much smaller than color.
- Color: needed for photos, stamps or colored signatures only.
Converting a text-only page from color to grayscale can shrink the file considerably.
Step 3: Choose the right format
For pages with photos or color, JPG at a quality of 70 to 85 is efficient. For text-only pages, a PNG with few colors, or a black-and-white format, can be smaller and sharper. Avoid TIFF and BMP unless you have a reason, as they’re typically large. See what is TIFF and JPG vs PNG vs WebP.
Step 4: Crop the margins
Scans often include dark edges and empty borders. Cropping to the page cuts unnecessary data and looks tidier. See crop vs resize.
Step 5: Combine into a PDF smartly
If your end result is a PDF, shrink each page image first, then combine them. The PDF will inherit the smaller sizes. See how to reduce PDF size.
Scanning old photos
Photos are different from documents. If you want to enlarge or print them later, scan at a higher resolution, such as 600 DPI for small prints, and keep a lossless master. Then make smaller JPG copies for sharing. The same “keep the original” rule from common resizing mistakes applies.
Keeping text readable
Zoom in to 100% on the result and read a few lines of small text. If it’s still clear, you’ve gone far enough. If not, raise the resolution a notch.
Privacy note
Scans of IDs, medical papers or financial documents are sensitive. Be thoughtful about which tools you use to process them, and delete copies you no longer need. See is it safe to use an online image resizer.
Quick settings guide
- Text document for email: 150 to 200 DPI, grayscale, JPG or PDF
- Archive copy: 300 DPI, keep the original
- Photo scan: 600 DPI master, JPG copies for sharing
Resize your scanned images with our online image resizer to get them down to size quickly.