How QR Codes Work

What a QR code actually is

A QR (Quick Response) code is a two-dimensional barcode. Unlike a traditional barcode that stores data in the width of lines, a QR code stores data in a grid of black and white squares, readable in two directions — which is why it holds far more information.

The black and white squares represent binary data: black for 1, white for 0. A typical QR code can store thousands of characters, depending on the version and error correction level.

What QR codes can store

• URLs: The most common use — a code that opens a website when scanned.
• Plain text: Messages, notes, or information you want to display.
• Wi-Fi credentials: Network name and password, so guests can connect without typing.
• Contact information: A vCard that adds someone's details to your phone.
• Phone numbers and email: Codes that initiate a call or compose a message.

How a phone reads a QR code

1. The camera captures the code — the phone's camera sees the pattern of black and white squares.
2. Software detects the code's position — the three large squares in the corners are finder patterns that tell the phone where the code is and how it's oriented.
3. The grid is decoded — each square is read as a binary value, and the resulting data is interpreted based on its type.
4. The phone acts on the data — opening a URL, displaying text, connecting to Wi-Fi, and so on.

What makes a QR code reliable

Error correction

QR codes include redundant data that allows them to be read even if part of the code is damaged or obscured. There are four error correction levels, from Low (7% recovery) to High (30% recovery). Higher error correction means the code can survive more damage but requires a denser grid.

Quiet zone

The white border around a QR code isn't decorative — it's essential. This "quiet zone" helps the scanning software distinguish the code from its surroundings. Without it, codes become harder to read.

Size and distance

A QR code needs to be large enough for the camera to resolve the individual squares. The farther away the scanner, the larger the code needs to be. As a rough guide, the scanning distance should be about 10 times the width of the code.

Static vs. dynamic QR codes

Static QR codes contain the data directly in the pattern. The data is fixed — if you want to change where a URL points, you need a new code. The advantage: the code works forever, with no service in the middle.

Dynamic QR codes contain a short redirect URL that points to a server you control. You can change the destination without changing the code. The trade-off: if the service goes down or you stop paying for it, the code stops working.