Guide

What is a QR Code? How They Work and What They Store

A QR code is a two-dimensional barcode that encodes text, URLs, contact details, and more. Learn how QR codes work, what the different parts mean, how much data they can hold, and when to use them.

What QR stands for

QR stands for Quick Response. QR codes were invented in 1994 by Denso Wave, a Toyota subsidiary, to track car parts during manufacturing. Unlike a traditional barcode which stores data in one direction, a QR code is two-dimensional — it stores data both horizontally and vertically, giving it far greater capacity.

A scanner (or any modern smartphone camera) reads the pattern of black and white squares and decodes the encoded data in milliseconds — hence “Quick Response”.

The anatomy of a QR code

Finder patternsThe three square corners (top-left, top-right, bottom-left). They let a scanner locate and orient the code from any angle.

Alignment patternA smaller square near the bottom-right. Helps correct for distortion when the code is printed on a curved surface.

Timing patternAlternating black/white lines between the finder patterns that define the grid size.

Data regionThe remaining squares encode the actual content using a specific binary encoding scheme.

Quiet zoneThe white border around the code. Scanners need this margin to distinguish the code from its surroundings — never remove it.

What data can a QR code store?

Data type	Example format	Use case
URL	https://datatoolkit.net	Link to a website
Plain text	Hello, world!	Notes, labels, signs
Email	mailto:hello@example.com	Pre-fill email recipient
Phone	tel:+441234567890	Click-to-call
SMS	smsto:+44…:message text	Pre-fill a text message
Wi-Fi	WIFI:T:WPA;S:MyNet;P:pass;;	Share Wi-Fi credentials
vCard	BEGIN:VCARD…	Share contact details
Geo location	geo:51.5074,-0.1278	Open a map location

A single QR code can store up to 4,296 alphanumeric characters or 7,089 numeric digits at the lowest error correction level.

Error correction — why QR codes still scan when damaged

QR codes use Reed-Solomon error correction, the same algorithm used in CDs and DVDs. This means a damaged, dirty, or partially obscured QR code can still be read — as long as enough of the pattern remains. There are four error correction levels:

Level	Data recovery	Best for
L	~7%	Clean environments, small codes
M	~15%	General use (default)
Q	~25%	Industrial environments
H	~30%	When adding a logo over the code

Higher error correction means a larger, denser code. If you are placing a logo in the centre of a QR code, use level H — the logo obscures part of the data, and the error correction recovers it.

Static vs dynamic QR codes

A static QR code encodes the destination directly in the pattern. Once printed, it cannot be changed — if the URL changes, you need a new code.

A dynamic QR code encodes a short redirect URL managed by a QR service. The destination can be updated without reprinting. Dynamic codes also enable scan analytics (location, device, time). They require a paid third-party service.

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