Reference
QR Code Reference
The rules behind a QR symbol — capacity, error correction, module size and payload formats — and a generator for each one.
Every entry maps to a real encoder decision
A QR code is not one format but a family of choices: version, error-correction level, mask, encoding mode and quiet zone. Each entry below explains one of those choices and what it changes in the printed symbol, so you can pick settings instead of accepting defaults.
Facts sourced from the standard
Numbers here follow ISO/IEC 18004 (QR Code Model 2) and the de-facto Wi-Fi payload convention used by Android and iOS. Capacity figures are maximums for a single symbol; real payloads lose space to headers and error correction.
All entries
QR error correctionFour levels — L, M, Q and H — trade payload capacity for tolerance of dirt, damage and glare.
QR code versionVersions 1 to 40 set the grid size, from 21×21 to 177×177 modules.
QR code capacityMaximum payload by mode and error-correction level, and why UTF-8 text uses more space than digits.
QR encoding modesNumeric, alphanumeric, byte, kanji and ECI decide how many bits each character costs.
QR quiet zoneFour empty modules on every side, required for the scanner to find the symbol.
QR mask patternOne of eight XOR patterns applied to data modules to avoid large blank or blocky areas.
QR format informationFifteen bits that tell the scanner the error-correction level and mask, protected by BCH.
QR structured appendSplitting one payload across up to sixteen linked symbols.
Micro QR codeA compact QR variant with one finder pattern, for very short payloads.
Wi-Fi QR code formatThe WIFI: payload string that joins a network without typing the password.
QR module sizeHow large each square must be printed for a camera to resolve it.
QR code print sizeChoosing a physical size from module count, scan distance and surface.
QR codes for binary and file dataWhen a QR code carries bytes rather than text, and why files rarely belong in one.