What the QR code standard specifies (ISO/IEC 18004)

A QR code is not a single vendor’s format. It is an international standard, which is why a code printed by one tool scans in any conformant reader. Knowing what the standard fixes, and what it leaves to you, makes the practical choices about size, error correction, and print quality much clearer.

What is the QR code standard?

QR codes are defined by ISO/IEC 18004. The current edition is ISO/IEC 18004:2024, the fourth edition, published in 2024, and it replaces the 2015 edition. The standard specifies the symbology: the character encoding, the symbol formats and dimensions, the error correction rules, and a reference decoding algorithm. It does not tell you what to put in the code or where to point it; that part is yours.

What are versions and modules?

The pattern is a grid of small squares called modules. The overall size is expressed as a version. Version 1 is 21 by 21 modules, and each higher version adds four modules per side, up to Version 40 at 177 by 177 modules. A higher version holds more data but takes more physical space, so a denser code is harder to scan at a distance or at small print sizes. In practice you want the lowest version that comfortably holds your data, which is another reason to keep the encoded value short.

What is error correction in the standard?

The standard defines four error correction levels, L, M, Q, and H, using Reed-Solomon coding so a reader can recover data from a code that is partly dirty or damaged. Higher levels tolerate more damage but spend more of the symbol on correction, so they need a higher version for the same data. DENSO WAVE documents Level M as restoring about 15 percent of the code and being the most commonly chosen, with Level Q at about 25 percent. The print and scanning guide covers how to pick a level for a given surface.

The quiet zone and the QR code family

The standard also fixes the quiet zone, the clear margin around the symbol that a reader needs to locate the code. It must be kept clear on all sides. ISO/IEC 18004 covers a family of related symbologies, not only the familiar QR code: Micro QR is a smaller member for tight spaces such as direct part marking, holding less data in less room.

None of this is affected by whether your code is static or dynamic. The barcode is the same standard either way. What a platform like redireo adds sits on top of the standard: a short link or a GS1 Digital Link encoded in a conformant symbol, resolving to a destination you control. If you are weighing a plain code against a Digital Link on a product, start with which kind of QR code you need.