What is a QR Code?
A QR code (Quick Response code) is a two-dimensional barcode invented by Denso Wave in 1994 for tracking car parts. Today, they're used everywhere — restaurant menus, product packaging, payments, and marketing campaigns — because smartphones can read them instantly with the camera.
How QR Codes Store Data
A QR code is made up of black and white squares (called modules) arranged in a grid. The data is encoded in these patterns using Reed-Solomon error correction.
Key structural elements:
- Finder patterns — The three square patterns in the corners that tell the scanner where the code starts and its orientation
- Alignment patterns — Help the scanner read distorted or curved codes
- Timing patterns — Alternating black/white lines that define the grid
- Data modules — The remaining squares that encode your actual data
QR Code Capacity
QR codes can store different amounts of data depending on the type of data and error correction level:
- Numeric only: up to 7,089 characters
- Alphanumeric: up to 4,296 characters
- Binary / UTF-8: up to 2,953 bytes
- Kanji: up to 1,817 characters
Error Correction Levels
QR codes have four levels of error correction, which determines how much of the code can be damaged or obscured while still being readable:
| Level | Data recovery | Best for |
|---|---|---|
| L (Low) | ~7% | Clean, undamaged codes |
| M (Medium) | ~15% | General use (default) |
| Q (Quartile) | ~25% | Industrial/logo overlay |
| H (High) | ~30% | Extreme conditions |
Higher error correction means the QR code has more squares and appears denser, but is more resilient to damage.
Best Practices for QR Codes
- Keep URLs short — Short URLs produce simpler, more scannable QR codes. Use a URL shortener if needed.
- Test before printing — Always test with multiple devices and apps before printing at scale.
- Minimum size — Print QR codes at least 2cm × 2cm (0.8in) for reliable scanning.
- Contrast matters — Dark code on light background. Avoid colors that reduce contrast.
- Add a call to action — Always tell people what the QR code does: "Scan to see our menu".
- Error correction level M or H — Use at least M if the code might get dirty or worn.
What Can QR Codes Link To?
- Website URLs
- WiFi credentials (SSID + password)
- Contact cards (vCard)
- Email addresses
- Phone numbers
- Calendar events
- SMS messages
- Plain text
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