What the finder pattern looks like
Each finder pattern is a 7 × 7 dark square ring, a 5 × 5 light ring inside it, and a solid 3 × 3 dark square in the center. A QR code has three of them, at the top-left, top-right and bottom-left corners.
Scanned along any line through its center, the pattern gives dark, light, dark, light, dark runs in a 1:1:3:1:1 ratio. That ratio stays the same whatever the rotation or distance, which is why a reader can spot it quickly in a camera frame.
- Size: 7 × 7 modules
- Center-line ratio: 1:1:3:1:1 (dark:light:dark:light:dark)
- Placed at three corners, never the bottom-right
- Surrounded on its inner sides by a 1-module light separator
How scanners use it
Once a reader has found all three finder patterns, it knows where the code is, how large it is and which way up it is. The missing fourth corner tells it the orientation, so a QR code can be scanned upside down or sideways.
The distance between finder patterns also gives a first estimate of the module size and version, which the reader then refines with the timing and alignment patterns.
Styling the corner squares
Designers often round the finder patterns or give them a different color. This usually works as long as the ring-in-ring structure and strong contrast survive, but it is the riskiest part of a code to change. The separator and quiet zone around each finder need to stay clear.