# Module

> A module is one square cell of a QR code — the smallest unit of the pattern. Codes are measured in modules, not pixels or millimetres, because the module count is fixed by the version and the physical size is whatever you print it at.

Source: https://useqr.app/glossary/module · Last reviewed 2026-08-21 · UseQR is free forever, MIT licensed, no signup.

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## Why modules matter more than pixels

Every scanning rule is really a rule about modules. A camera needs roughly **2–3 pixels
per module** to decode reliably, and a printer needs the module to survive ink spread.
So the two questions that decide whether a code works are: how many modules does my
payload need, and how many millimetres will each one be?

| Version | Modules across | At 0.5 mm/module | At 1 mm/module |
|---|---|---|---|
| 1 | 21 | 10.5 mm | 21 mm |
| 5 | 37 | 18.5 mm | 37 mm |
| 10 | 57 | 28.5 mm | 57 mm |
| 20 | 97 | 48.5 mm | 97 mm |
| 40 | 177 | 88.5 mm | 177 mm |

A practical floor for consumer printing is **0.4 mm per module**; below that, ink spread
and camera resolution start eating the pattern. See [size for print](/docs/print/qr-code-size-for-print).