# Version information: how big symbols declare their size

> Version information exists only in QR versions 7 to 40: an 18-bit word made of 6 version bits plus 12 BCH(18,6) check bits, written twice: a 6×3 block above the bottom-left finder and a 3×6 block left of the top-right finder. Versions 1–6 rely on module counting instead.

Source: https://useqr.app/docs/spec/version-information · Last reviewed 2026-08-21 · UseQR is free forever, no signup.

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## Only from version 7

QR versions 1–6 carry no version field at all. Their size is small enough that a decoder
can establish it by measuring: count the modules along the
[timing patterns](/docs/spec/timing-patterns), or divide the distance between finder
centres by the measured module pitch. At 21–41 modules per side, the difference between
adjacent versions (4 modules) is a large, safe fraction of the whole.

From **version 7 (45 × 45)** upward the arithmetic gets fragile: a small pitch
misestimate across a large symbol can land on the wrong version, and a wrong version means
a wrong sampling grid, wrong [alignment pattern](/docs/spec/alignment-patterns) positions
and wrong block structure. So versions 7–40 state their version explicitly, with heavy
protection.

## The 18-bit word

| Bits | Content |
|---|---|
| 6 | Version number, 7–40 in binary (000111 to 101000) |
| 12 | BCH(18,6) error-correction bits |

Unlike [format information](/docs/spec/format-information), no XOR mask is applied: the
version bits are never all zero, since the field only exists from version 7.

Worked example: version 7 is `000111`; the BCH remainder extends it to
**`000111110010010100`**. Version 8 encodes to `001000010110111100`. The BCH(18,6) code has
minimum distance 8, so a decoder can correct up to **3 bit errors** in each copy, and, as
with format bits, there are only 34 valid words, so exhaustive nearest-match against the
full list is a practical last resort.

## Where it lives

Written **twice**, in mirror-image positions:

- a **6 × 3 block** immediately above the bottom-left finder pattern,
- a **3 × 6 block** immediately left of the top-right finder pattern.

Both sit inside the corner regions a scanner has already located before it needs the
version, which is the point: the decoder reads finders, then version, then builds the
grid, then reads [format information](/glossary/format-information), then data.

## Why redundancy here matters

The version field is the decoder's declaration of geometry. Get it wrong by one and every
downstream structure shifts: the symbol claims a different module count, the alignment
grid lands in the wrong places, and the [codeword](/glossary/codeword) count changes. There
is no graceful degradation. It either matches reality or nothing decodes. Hence the same
defensive design as format bits: strong BCH, two copies, tiny valid-word space.

For designers the practical consequence is one more pair of keep-clear zones. Styling that
crowds the top-right or bottom-left finder on a **version 7+** code: large payloads,
[bulk-generated](/bulk) vCards, long URLs, risks bits that error correction in the data
region cannot help with. If your payloads are long enough to push past version 6, check
where they land with the [version and module table](/docs/reference/qr-code-version-and-module-table)
and [verify the styled output](/validate).

## FAQ

### What is version information in a QR code?
An 18-bit field present only in versions 7–40: six bits stating the version plus twelve BCH(18,6) check bits. It is written twice, above the bottom-left finder and left of the top-right finder, so the decoder knows the symbol size without measuring.

### Why do small QR codes not have version information?
Versions 1–6 are small enough that decoders determine the size reliably by counting timing-pattern modules. The explicit field only becomes necessary at version 7, where measurement error across a large symbol could land on the wrong size.

### How many errors can the version field survive?
Up to 3 bit errors per copy, thanks to the BCH(18,6) code's minimum distance of 8, and there are two copies. Decoders can also compare a damaged read against all 34 valid version words and take the closest match.

### Can I tell a QR code's version by looking at it?
Yes, count the modules along one side and apply size = 4 × version + 17. A 25-module side is version 2; a 45-module side is version 7, the first version that also carries the explicit field.

## Try it

- https://useqr.app/url
- https://useqr.app/validate
- https://useqr.app/scan