1. Dots, Not Millimeters
A 203 dpi printhead lays down about 8 dots per mm, so one dot is about 0.125 mm. A 300 dpi head has dots about 0.085 mm. Use our [QR size calculator](/qr-size-calculator) to convert between dots and physical dimensions.
2. Use Whole-Dot Modules
Fractional scaling creates uneven modules. Pick an integer number of dots per module:
* 203 dpi, 4 dots per module = 0.5 mm
* 300 dpi, 6 dots per module = about 0.51 mm
3. Worked Example
A Version 2 code (25 modules) plus an 8-module quiet zone is 33 modules. At 4 dots each on 203 dpi:
$$33 \times 4 = 132\text{ dots} \approx 16.5\text{ mm}$$
Generate codes with our [URL QR code generator](/url-qr-code-generator) or [barcode generator](/barcode-generator) at the calculated exact pixel dimensions.
4. Tips
Set darkness and speed so modules neither fade nor bloom, and print the code from a vector or exact-pixel bitmap, not a resampled image. Test output with a [QR scanner](/qr-scanner) and verify quality using our [printed QR tester](/printed-qr-tester) methodology. Follow our [QR placement guide](/qr-placement-guide) for label positioning. Use our [error correction simulator](/error-correction-simulator) to understand how thermal print quality affects readability.
Putting this into practice
Start with the smallest real test you can run. Generate the code, print it at the exact size you plan to use, and scan it with two different phones in the lighting where it will live. Check that the destination page loads quickly on a mobile connection and that the call to action next to the code tells people what they will get. If anything feels slow or unclear, fix it before you print a full batch, because reprints cost more than a short test. Keep a note of the size, material, and placement that worked so the next batch starts from a proven setup.
Common mistakes to avoid
The most common mistakes are easy to avoid once you know them. Long payloads make modules tiny, low contrast makes edges hard to read, and text placed too close to the border eats the quiet zone the scanner needs. Covering a corner finder pattern with a logo or a sticker breaks detection entirely, and a code placed behind glare or on a curved surface fails even when the print is perfect. Review each of these points on a proof copy, and treat any failure as a reason to adjust the design rather than a reason to blame the scanner.
Quick checklist
- Keep the payload as short as practical so modules stay large.
- Keep dark modules on a light background with strong contrast.
- Leave a clear quiet zone on all four sides of the symbol.
- Test the printed code at the real viewing distance and lighting.
- Confirm the destination page loads fast on a phone.
- Recheck the code after any change to the link, design, or placement.
