What is a QR Code?
A QR code (Quick Response code) is a two-dimensional barcode that can store various types of data — URLs, text, contact information, WiFi credentials, and more. QR codes can be read by smartphones, tablets, and dedicated scanners in any orientation.
How QR Codes Store Data
QR codes store data in a matrix of black and white squares. The data is encoded using Reed-Solomon error correction, which allows the code to be read even if part of it is damaged or obscured.
Error Correction Levels
| Level | Name | Recovery Capacity | Use Case |
|---|---|---|---|
| L | Low | 7% | Clean environments, digital displays |
| M | Medium | 15% | General use (default) |
| Q | Quartile | 25% | Industrial environments |
| H | High | 30% | Printed materials, damaged surfaces |
Data Types You Can Encode
| Type | Format | Example |
|---|---|---|
| URL | Plain URL | https://freeutil.app |
| Plain text | Plain text | Hello World |
mailto: | mailto:hello@example.com | |
| Phone | tel: | tel:+6612345678 |
| SMS | smsto: | smsto:+6612345678:Hello |
| WiFi | WIFI: | WIFI:T:WPA;S:MyNetwork;P:password;; |
| Contact | vCard | BEGIN:VCARD... |
Best Practices
- Size: Minimum 2x2 cm for print; larger for farther scanning distances
- Contrast: Dark code on light background — avoid colors that reduce contrast
- Quiet zone: Keep a white border (at least 4 modules wide) around the code
- Test before printing: Always test with multiple devices before printing at scale
- Short URLs: Use URL shorteners for long URLs — shorter data = simpler, more scannable code
- Error correction: Use Level H when adding a logo in the center
✓ Adding a logo to the center of a QR code is fine — use error correction Level H which allows up to 30% of the code to be obscured. Keep the logo area under 25% of the total QR code area.