Applies to: Ordinary reflective paper and photographic prints. The pixel examples are calculated, not scans or device benchmarks. Institutional preservation specifications take precedence.
Use 300 DPI for ordinary documents, receipts, OCR, and most sharing. Use 600 DPI for small photographs, fine line art, tiny text, or originals you may crop and enlarge later.
What DPI changes
DPI describes how many samples the scanner records per inch of the original. A 6 × 4 inch photo scanned at 300 DPI becomes about 1800 × 1200 pixels. At 600 DPI, it becomes about 3600 × 2400 pixels—four times as many pixels in total.
More samples can preserve finer detail, but they also increase scan time, memory use, and file size. Higher DPI cannot restore detail that is absent from a blurred or low-quality original.
Choose by source material
Text documents and forms are usually fully legible at 300 DPI. OCR software also performs well when characters are sharp and the page is straight. For tiny print, stamps, detailed illustrations, or photographs that will be cropped, 600 DPI provides more room to work.
- Documents and receipts: 300 DPI, grayscale or black and white.
- Color office pages: 300 DPI, color, moderate JPEG quality or PDF compression.
- Small photographic prints: 600 DPI, 24-bit color.
- Line art and diagrams: 600 DPI, grayscale or monochrome depending on the scanner.
- Large photos for same-size viewing: 300 DPI is generally sufficient.
Do not confuse scan DPI with print DPI
A scan’s pixel dimensions determine how large it can be printed. If an image is 3000 pixels wide, it can print 10 inches wide at 300 pixels per inch or 5 inches wide at 600 pixels per inch.
Printer manufacturers may advertise much higher ink-placement numbers. Those figures describe how the printer places droplets, not how many unique image pixels your scan needs.
Run a two-scan test
If the original is important, scan a small detailed area at both settings. View each at the same physical size and print a sample if printing is the final use. Keep 600 DPI only when it reveals useful detail.
For long-term preservation, keep a high-quality master and create smaller copies for email or web use.
Compare pixels at the same physical output size
A 6 × 4 inch original sampled at 300 pixels per inch contains 2.16 million pixels. At 600 it contains 8.64 million. Doubling each dimension makes four times the samples, but does not guarantee four times the useful detail or four times the compressed PDF size.
The byte calculation assumes 8-bit red, green and blue: width × height × 3. It excludes headers, metadata, padding, OCR and compression. Scanner controls commonly label the sampling setting DPI.
| Scan setting | Pixel dimensions | Uncompressed RGB bytes |
|---|---|---|
| 300 PPI | 1800 × 1200 | 6,480,000 bytes |
| 600 PPI | 3600 × 2400 | 25,920,000 bytes |
Run a comparison you can reproduce
Choose a sample with the smallest writing and faintest marks in your actual job. Scan it twice without changing color mode, crop or compression quality. Record the scanner model, application version, resolution, color setting, file format and file size.
Compare the outputs at the same intended print size. Viewing both at 100% on a screen displays the 600 PPI image at twice the linear size, which is not an equal comparison. Check whether a decimal point, thin line or faint annotation becomes readable, rather than judging apparent sharpness alone.
- Keep both original scan files.
- Reopen each file and inspect pixel dimensions.
- Compare equivalent areas at the same display size.
- For OCR, compare a few known names and numeric values.
- Choose the lower setting if it preserves every necessary detail.
- Keep a larger master only when the additional detail serves a real purpose.
When a higher setting does not solve the problem
If both files look blurred, check focus, motion, glass cleanliness and whether the scanner is using an interpolated setting. If text is pale, color mode and thresholding may matter more than sample density. If pages are crooked, correct the physical feed before increasing resolution.
Film and very small originals are different tasks: their enlargement requirements can exceed the two settings discussed here. Check the capture equipment and intended reproduction size rather than treating 600 as a universal maximum.
Sources and further reading
Vendor instructions and background references are linked below. Worked examples are our explanatory calculations, not vendor performance claims. Check the instructions for your current software and device.
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