QR stands for Quick Response. A QR code is a two-dimensional barcode — a square grid of black and white modules that encodes information. Unlike a traditional barcode which stores data in one direction (horizontal lines), a QR code stores data both horizontally and vertically, allowing it to hold much more information in less space.
A Brief History
QR codes were invented in 1994 by Denso Wave, a subsidiary of Toyota, to track vehicles and parts during manufacturing. The standard barcode wasn't fast or dense enough for their needs, so they created a 2D barcode that could be read from any angle and hold thousands of characters.
The technology was made freely available — Denso Wave chose not to enforce their patent rights. This decision is why QR codes are everywhere today. Anyone can create and use them without licensing fees.
How Data Is Stored
A QR code encodes data as a pattern of dark and light modules (the small squares). The data is converted to binary, then mapped onto the grid following a specific standard (ISO/IEC 18004).
A QR code contains several functional areas:
Finder patterns. The three large squares in three corners. These help the scanner locate and orient the QR code — it can be read at any angle or rotation.
Alignment patterns. Smaller squares that help correct for distortion if the QR code is on a curved surface or photographed at an angle.
Timing patterns. Alternating dark and light modules between the finder patterns. They help the scanner determine the module size and grid dimensions.
Data and error correction area. The rest of the QR code — this is where your actual data lives, along with error correction codes.
Format and version information. Encoded near the finder patterns, telling the scanner which error correction level and encoding mode was used.
How Phones Read QR Codes
When you point your phone's camera at a QR code, here's what happens:
- The camera captures an image of the QR code
- The software locates the three finder patterns to determine the QR code's position, size, and orientation
- It reads the format information to determine the error correction level and data encoding
- It decodes the data modules row by row
- It applies error correction to fix any damaged or unreadable modules
- The decoded data (URL, text, contact info, etc.) is presented to the user
This entire process happens in milliseconds. Modern phones since roughly 2017 have QR scanning built into the default camera app — no separate app needed.
What Can a QR Code Store?
QR codes can encode several types of data:
URLs — the most common use. Opens a website in the browser.
Plain text — any text string up to about 4,000 characters.
vCard — contact information that the phone offers to save to the address book.
WiFi credentials — network name, password, and encryption type. The phone offers to connect automatically.
Email — a pre-filled email with address, subject, and body.
Phone numbers — the phone offers to call the number.
SMS — a pre-filled text message with number and body.
Geographic coordinates — opens a location in maps.
The maximum capacity depends on the data type. For numeric data, a QR code can hold up to 7,089 characters. For alphanumeric, up to 4,296. For binary data, up to 2,953 bytes. In practice, shorter data creates a simpler, more scannable QR code.
Error Correction
One of the most useful features of QR codes is built-in error correction using Reed-Solomon codes. There are four levels:
- L (Low) — recovers up to 7% of data
- M (Medium) — recovers up to 15% of data
- Q (Quartile) — recovers up to 25% of data
- H (High) — recovers up to 30% of data
Higher error correction means the QR code can be partially damaged, dirty, or even have a logo placed over part of it and still scan correctly. The trade-off is that higher correction creates a denser QR code.
Why QR Codes Are Everywhere Now
Several factors drove the explosion of QR codes in recent years. Smartphones got built-in QR scanning in their cameras. The pandemic accelerated contactless interactions — restaurants switched to QR menus, payments went contactless. And the technology is free, open, and works across all devices and platforms.
Today, QR codes are used in restaurants, retail, marketing, events, healthcare, logistics, education, payments, and dozens of other industries. They bridge the physical and digital worlds in a way that no other technology does as simply.
Create Your Own QR Code
Ready to try it? Go to qree.app and create a QR code in seconds — for URLs, contacts, WiFi, and more.