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Glossary

Numeric mode

Numeric mode is the most compact QR encoding: digits are taken in groups of three, each group packed into 10 bits, about 3.33 bits per digit against 8 in byte mode. It applies only when the entire segment is 0–9, and it is why the famous 7,089-character capacity ceiling is digits-only.

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How the packing works

Three digits form a number from 0–999, which fits in 10 bits. A leftover pair takes 7 bits and a final single digit 4 bits. The segment opens with the mode indicator 0001 and a character count. So 20260821 (8 digits) costs 10 + 10 + 7 = 27 bits of data: byte mode would spend 64.

That 2.4× density is where the headline capacity figure comes from: 7,089 digits at version 40-L, against 2,953 bytes. The exact values per character are compared in the character set reference.

When generators actually use it

Encoders pick the cheapest mode automatically, UseQR's encoder tests the payload against ^[0-9]+$ and selects numeric mode when it matches. One non-digit anywhere disqualifies the segment:

  • 4477009001 → numeric mode.
  • +4477009001 → the + forces byte mode for the segment (a phone-number payload is tel:+…, so it never qualifies anyway).
  • 2026-08-21 → the hyphens push it to alphanumeric.

In practice numeric mode appears in serials, ticket numbers, and bulk-generated ID codes, payloads you control. If you can define an identifier scheme, digits-only buys the smallest possible symbol; you can confirm the mode a real code used by decoding it.

FAQ

How many numbers can a QR code hold?

Up to 7,089 digits at the largest version with error correction level L, but only if the payload is exclusively the characters 0–9, which enables numeric mode's 3.33 bits per digit.

Why did adding one letter make my QR code bigger?

A single non-digit character disqualifies numeric mode, and the segment falls back to alphanumeric (5.5 bits per character) or byte mode (8 bits), producing a denser, higher-version code for the same length.

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Related

  • Alphanumeric mode, Alphanumeric mode encodes a fixed 45-character set at 5.5 bits per character (two characters per 11 bits), with no lowercase letters in the set.
  • Byte mode, Byte mode stores arbitrary 8-bit data: the workhorse encoding for URLs and mixed text, nominally ISO 8859-1 but UTF-8 in universal practice.
  • 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…
  • 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…