How Do QR Codes Work?

How Do QR Codes Work?

Aswanth Alakkadan
May 23, 2025
5 min read

QR codes, or Quick Response codes, are two-dimensional barcodes that store data in a square grid of black and white squares. They can be scanned using smartphones or QR code readers, and are widely used for everything from payments and product tracking to website links and contactless menus. But how do these tiny squares actually work?

What Is a QR Code?

A QR code is essentially a type of matrix barcode that can hold a large amount of information compared to traditional barcodes. Developed in 1994 by Denso Wave (a Toyota subsidiary), QR codes were designed to allow fast decoding and robust error correction.

Each QR code contains encoded data in both horizontal and vertical directions, making it possible to scan them from any angle.

Structure of a QR Code

A standard QR code is made up of several components:

  • Finder Patterns: The large squares at three corners help the scanner determine the orientation.
  • Alignment Pattern: Helps with the correction of distortion.
  • Timing Pattern: Alternating black and white modules that help locate the data cells.
  • Format Information: Stores information about the error correction level and mask pattern.
  • Version Information: Indicates the QR code version (size of the grid).
  • Data and Error Correction Keys: Store the actual encoded data and error-correction information.

How Data Is Encoded

  1. Data Input: You enter text, a URL, or other data into a QR code generator.
  2. Encoding: The data is converted into binary and arranged into the grid.
  3. Error Correction: Error correction bits are added using Reed-Solomon algorithms. This allows the QR code to be readable even if it's partially damaged.
  4. Masking: A mask pattern is applied to make the code easier to scan under different lighting conditions.
  5. Final Output: The complete grid is generated and rendered as a QR code image.

How Scanning Works

  1. Camera Capture: A smartphone or scanner takes a photo of the QR code.
  2. Detection: The device identifies the finder patterns to determine the orientation.
  3. Decoding: The scanner reads the data modules, decodes the binary, and applies error correction.
  4. Action: The decoded information is interpreted—e.g., a URL is opened in a browser.

Common Uses of QR Codes

  • Payments (UPI, PayPal, etc.)
  • Product packaging and tracking
  • Marketing and promotions
  • Wi-Fi access sharing
  • Digital business cards (vCards)

Fun Fact

QR codes can store up to:

  • 7,089 numeric characters
  • 4,296 alphanumeric characters
  • 2,953 binary bytes

Conclusion

QR codes are a smart and compact way to bridge the physical and digital world. With their ability to store a significant amount of information and resist damage, they've become a staple in modern communication and commerce.

Next time you scan a QR code, you'll know the fascinating mechanics behind how it works!