QR Code Error Correction: How Damaged Codes Still Work

One of the most remarkable features of QR codes is their ability to be read even when partially damaged, dirty, or obscured. This reliability comes from built-in error correction using Reed-Solomon codes.

How Error Correction Works

QR codes use Reed-Solomon error correction, the same mathematical technique used in CDs, DVDs, and deep-space communication. The algorithm adds redundant data to the QR code that allows the scanner to reconstruct missing or corrupted information.

Error Correction Levels

QR codes offer four error correction levels, each providing different amounts of redundancy.

Level L (Low) - 7% Recovery

The minimum error correction level. Best for clean, controlled environments where the code will not be damaged. Allows the maximum data capacity.

Level M (Medium) - 15% Recovery

The default level for most applications. Provides a good balance between data capacity and damage resistance. Suitable for most printed materials.

Level Q (Quartile) - 25% Recovery

Good for environments where codes may get partially obscured or dirty, such as warehouse labels or outdoor signage.

Level H (High) - 30% Recovery

The maximum error correction level. Required when placing logos or images in the center of the QR code. Also recommended for industrial applications where damage is likely.

Practical Implications

With Level H error correction, up to 30% of the QR code can be damaged or covered and it will still scan correctly. This is why you can place a small logo in the center of a QR code and it still works, as long as you do not cover more than the error correction can handle.

Choosing the Right Level

Use Level L for maximum data in controlled environments. Use Level M for general-purpose applications. Use Level Q or H for outdoor use, industrial applications, or when adding visual elements to the code. Our generator uses Level M by default, providing reliable performance for most use cases.