# Finder pattern

> The three large concentric squares in the corners of a QR code are finder patterns. A scanner locates them first to work out where the code is, how big it is and which way up it is — which is why the missing fourth corner is deliberate.

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

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## The 1:1:3:1:1 ratio

Each finder pattern is a 7 × 7 module block: a black 7 × 7 square containing a white
5 × 5 square containing a black 3 × 3 square. Scanned along any line through the centre,
the black-white ratio is **1:1:3:1:1** — a signature that is rare in natural images and
survives rotation, which is what makes QR codes findable at any angle.

## Why only three corners

Three points define an orientation; a fourth would be redundant. The empty bottom-right
corner is how a scanner knows which way up the code is. This is also why you cannot
"balance" a design by adding a fourth square — it breaks detection.

## Styling them

Finder patterns tolerate rounding and colour changes provided the 1:1:3:1:1 ratio survives
at the sampling resolution and contrast stays high. Filling the centre square with a logo
does not survive. UseQR verifies styled output by decoding it before download, which is
the only way to know a styled finder still reads.