# QR Code

*Quick Response code* · Software

> A QR code is a two-dimensional matrix barcode (ISO/IEC 18004) that stores data in square modules and can be read quickly by a phone camera.

The QR (Quick Response) code was developed in 1994 by the Japanese company Denso Wave to track automotive parts and became an international standard as ISO/IEC 18004. Finder patterns in three corners let it be read quickly from any angle. Sizes range from 21×21 modules in version 1 to 177×177 modules in version 40. The largest version at the lowest error-correction level holds 7,089 digits or about 2,950 bytes of data.

QR codes use Reed–Solomon error correction with four levels: L (about 7% of data recoverable), M (15%), Q (25%) and H (30%). A code therefore stays readable even if partly dirty or overlaid with a logo in the centre. Use level Q or H when adding a logo. Leave a quiet zone at least 4 modules wide around the code and print dark modules on a light background with good contrast. Print size depends on scanning distance. A common rule of thumb is that the distance should not exceed roughly 10 times the code's width.

A static QR code contains the data itself and cannot be changed once printed. A dynamic QR code holds a short redirect URL, so the destination can be updated without reprinting and scan statistics can be collected. Key uses include QR menus and table ordering in restaurants, room information in hotels, sharing Wi-Fi credentials, digital business cards and payments. In Türkiye, payments use the TR Karekod standard, while the karekod printed on medicine boxes is technically a GS1 DataMatrix code.

The most common security risk is a fake sticker placed over a genuine code to send users to phishing sites (quishing). Businesses should use their own domain and inspect codes regularly, and users should check the address that opens. With dynamic codes, a provider discontinuing its service can break every printed code, so redirects are best run through a domain the business controls.

---
Canonical: https://internetten.com.tr/en/glossary/qr-code