Document Scanning DPI Resolution & OCR Storage Estimator
Optimize scan DPI (150, 300, 600 DPI), color modes, text OCR recognition accuracy, and long-term digital archiving size.
OCR scan file size by DPI and colour mode: method and example
Total volume = number of pages × (average compressed page size + 8 KB of OCR text layer). The tool uses 45 KB per A4 page in black and white at 300 DPI, 180 KB in greyscale and 400 KB in colour: 5,000 black-and-white pages come to about 259 MB, against 1.95 GB in colour.
Page size assumptions
| Mode | 150 DPI | 300 DPI | 600 DPI |
|---|---|---|---|
| Black and white | 25 KB | 45 KB | 120 KB |
| Greyscale | 80 KB | 180 KB | 450 KB |
| 24-bit colour | 150 KB | 400 KB | 1,200 KB |
These average compressed A4 page sizes are flat values used by the tool, which adds 8 KB of text layer per page. Processing time is 0.8 seconds per page and cloud cost multiplies gigabytes by 0.023.
Example
5,000 black-and-white pages at 300 DPI: 5,000 × 53 KB ÷ 1,024 = 259 MB, about 67 minutes of processing, cloud cost shown as 0.01 per month (the floor value). The same pages in colour: 408 KB per page, 1.95 GB.
What French tax rules require
For a scanned paper invoice to replace the original in France, the copy must reproduce the document identically: colours kept when they carry meaning (stamp, signature, annotation), no image processing, lossless compression only. A black-and-white scan or a lossy one (JBIG2 or JPEG in lossy mode) may therefore fall short. The recommendation shown under the result ("300 DPI black and white or grayscale", lossless compression) is common practice, not a requirement of that text.
Limits
- A4 only, with no choice of compression format: page sizes are flat values.
- Cloud cost uses Amazon S3 Standard's first-tier dollar price and shows it in dollars, excluding requests and transfers.
- Real file size depends on the scanner, page content and compression software.
Sources and dates: article A102 B-2 of the French Livre des procédures fiscales, created by the order of 22 March 2017, version in force since 31 March 2017. S3 Standard price of $0.023 per GB-month (US East, first 50 TB): indicative value, not verified on AWS's pricing page (checked 14/10/2026).
Frequently Asked Questions
What resolution should I use to scan documents for OCR?
300 DPI is the tool's default and the usual compromise for printed text. 150 DPI is enough for a preview; 600 DPI suits small print or archive documents, at the cost of a file about 2.7 times heavier in black and white (120 KB against 45 KB per page).
How big are 1,000 scanned pages as PDF?
Using the tool's assumptions at 300 DPI: about 52 MB in black and white (53 KB per page including the OCR layer), 184 MB in greyscale and 398 MB in colour. Actual size varies with the scanner and page content.
Can I scan an invoice in black and white and destroy the original?
Under French tax rules (article A102 B-2 of the Livre des procédures fiscales), the copy must be identical: colours that carry meaning (stamp, signature, annotation) must be kept, and only lossless compression is allowed. A black-and-white scan is acceptable only if the original's colours carry no information; other countries have their own rules.
How much does cloud storage for scanned archives cost?
The tool multiplies the volume in gigabytes by 0.023, the monthly first-tier price of Amazon S3 Standard in dollars, with a minimum of 0.01. 50,000 colour pages at 600 DPI (57.6 GB) thus cost about 1.32 a month, excluding request and transfer fees.
Is this tool really free?
Yes, all tools on Kristools are 100% free and accessible without registration.
Is my data protected?
Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.