Glossary
Data capacity
Data capacity is how much a QR code can hold, and it depends on three things at once: the version, the error-correction level and the encoding mode. The maximum is 7,089 digits, 4,296 alphanumeric characters or 2,953 bytes.
The absolute maxima (version 40, level L)
| Mode | Maximum |
|---|---|
| Numeric | 7,089 digits |
| Alphanumeric | 4,296 characters |
| Byte (UTF-8) | 2,953 bytes |
| Kanji | 1,817 characters |
At level H those figures drop to 3,057 / 1,852 / 1,273 / 784.
The practical ceiling is much lower
A version-40 code is 177 modules across. To be scannable by a phone at arm's length, each module wants roughly 0.5 mm, giving a 9 cm square. Most real applications should stay under about 300 bytes.
The cheapest capacity win
Switch modes. Uppercase alphanumeric costs 5.5 bits per character; byte mode costs 8. A URL
written HTTPS://EXAMPLE.COM/SALE encodes about 45% more efficiently than the lowercase
equivalent — free capacity for no design change. Paths remain case-sensitive on most
servers, so only uppercase the scheme and host.
Related
- Version — A QR code's version is its size: version 1 is 21 × 21 modules and each step adds 4 modules per side, up to version 40 at 177 × 177. The encoder picks the…
- Encoding mode — Encoding mode is how characters are packed into bits. QR codes support numeric (3.33 bits/char), alphanumeric (5.5), byte (8) and kanji (13), and a single…
- Error correction level — Error correction level sets how much of a QR code can be damaged and still decode: L tolerates about 7%, M 15%, Q 25% and H 30%. Higher levels cost…