What Is a QR Code? A Plain-English Guide

QR codes are everywhere — on menus, posters, packaging and business cards. But what actually is a QR code, and how does that little square of dots hold your website address?

The short version

A QR ("Quick Response") code is a two-dimensional barcode. Where an old-fashioned barcode stores a few digits in a row of vertical lines, a QR code stores data in a grid of black and white squares called modules. Because it works in two dimensions, it can hold far more — a full URL, contact details, Wi-Fi credentials, or a payment address.

How the data is stored

The pattern is not random. Every QR code has three large squares in the corners called finder patterns. These let a camera detect the code and work out its orientation, even at an angle. Smaller alignment patterns keep the grid readable on curved surfaces, and timing rows tell the scanner how big each module is.

The rest of the grid encodes your data plus error-correction information.

Why error correction matters

QR codes use Reed–Solomon error correction. In practice this means a code can still be read even if part of it is dirty, torn, or covered by a logo. There are four levels — L, M, Q and H — recovering roughly 7%, 15%, 25% and 30% of the code respectively. Higher correction means a busier pattern but a more robust code, which is exactly why adding a logo in the center still works.

Why businesses use them

• They bridge print and digital — a scan takes someone from a flyer straight to your site.
• They are free to generate and cost nothing to print.
• They are contactless, which made them indispensable for menus and payments.
• They are measurable when you route them through a tracked link.

Once you understand the anatomy, the rest is easy: choose what the code should do, keep the contrast high, and test it before you print.