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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…