The short answer
A QR (Quick Response) code is a two-dimensional barcode invented in 1994 for the automotive industry. Unlike a one-dimensional barcode, which stores data in a single row of lines, a QR code stores data in a grid of black and white squares called modules — typically 21×21 up to 177×177.
Scanning a QR code with a phone camera instantly opens whatever it encodes: a website, a WiFi login, a contact card, a calendar event, or plain text. That instant jump from physical to digital is why QR codes are everywhere today.
How a QR code is built
A QR code has three big square “finder patterns” in the corners that let a scanner locate and orient the code, a smaller alignment pattern for skewed scans, timing patterns that connect them, and a data area in between that holds the encoded bits plus error-correction data.
Error correction uses Reed-Solomon codes so the code still scans even when part is damaged or covered — for example by a logo. There are four levels: L (~7% recovery), M (~15%), Q (~25%), and H (~30%).
What QR codes can store
A QR code can hold up to about 2,953 bytes of binary data, roughly 4,296 alphanumeric characters, or 7,089 digits. In practice people encode URLs, WiFi credentials (WIFI:), vCards, SMS/email shortcuts, calendar events (VEVENT), and arbitrary text.
The more data you encode, the denser the grid and the harder it is to scan at small sizes — which is why short links are recommended for QR codes.
Frequently asked questions
What does QR stand for?
Quick Response. The name comes from the codes’ ability to be read quickly and from any angle.
Do QR codes need internet to scan?
No. Reading a QR code is instant and offline. You only need internet if the code opens a web link.
Can a QR code be any color?
Yes, as long as there is strong contrast between the dark and light modules. Low-contrast codes are hard to scan.
Who invented the QR code?
Masahiro Hara at Denso Wave (a Toyota subsidiary) in 1994, originally to track car parts.