Module

A QR code of version V is 17 + 4V modules across, from 21 × 21 (441 modules) at version 1 to 177 × 177 (31,329 modules) at version 40. In the data area a dark module is a binary one and a light module a binary zero.

Not every module carries data. The finder patterns, their light separators, the timing and alignment patterns and the format information occupy fixed positions. What remains is the encoding region, where every 8 modules hold one codeword of data or error correction. In a version 1 code, 208 of the 441 modules carry codewords: 26 codewords of 8 bits each.

The width of one module is often called the X-dimension. Decoders estimate it from the finder patterns and then sample each module near its center, which is why rounded or dot-shaped modules can still scan, provided the dots are large enough and the contrast is strong.

A code’s printed width is its module count times the module size, so the two trade against each other. Put more content in a code and it needs more modules; print it at the same width and every module gets smaller, which shortens the distance it can be scanned from and makes it more sensitive to blur, ink spread and low resolution.

That is the practical reason to keep content short, for example with a short URL, and to print dense codes larger. Export vector files (SVG or PDF) for print so module edges stay sharp, and keep every module the same size: hand-editing or stretching a code breaks the grid the scanner expects.

A 28-character short link at error correction level M makes a version 3 code, 29 modules across. Printed 2.5 cm wide (not counting the quiet zone), each module is about 0.86 mm. The same width holding a 90-character link with campaign tags (version 6, 41 modules) leaves each module about 0.61 mm, roughly 30% smaller.