How a QR Code Is Built: Finder Patterns and Modules

A QR code looks like random noise, but every part has a job. Understanding the layout explains why scanning works so quickly.

The basic unit: the module

A QR code is a square grid of small black and white squares called modules. Each module stores one bit of information. The smallest standard QR code is 21 × 21 modules.

The three corner squares

The large squares in three corners are finder patterns. Your phone looks for them first. Because there are three, and not four, the scanner can tell which way the code is rotated. This is why you can scan a QR code upside down or at an angle.

Alignment and timing patterns

• Timing patterns are alternating black and white lines running between the finder patterns. They help the scanner work out the size of each module.
• Alignment patterns are small squares inside larger codes. They help the scanner correct for a code that is bent or photographed at a slant.

Format information

Strips of modules near the finder patterns record which error-correction level and mask pattern were used. A mask is applied to the data so that it does not form large solid blocks or confusing patterns that could fool a scanner.

The data area

The rest of the grid holds the message and the error-correction data. The message might be a web address, some text, a Wi-Fi login or a contact card. The code itself does not care what the content means. The scanner decodes the bits, then your phone decides what to do with the result.

The quiet zone

Around the whole code there must be an empty white border, called the quiet zone. Without it, the scanner cannot tell where the code ends and the background begins.

Why this matters to you

• Do not crop the corners when you save or print a code.
• Keep the border clear of text and pictures.
• Expect it to work sideways. The finder patterns handle rotation.

QR Code Scanner opens straight to the camera, so you can point it at any code and get the result at once.

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