QR Code Character Encoding

QR Code Encoding

The method by which the characters are converted into bits of data and stored in a QR code

  • There are four standard encoding modes used by QR codes: numeric, alphanumeric, binary and kanji.
  • This tool demonstrates numeric, alphanumeric and binary encoding.
  • All characters can be encoded using binary encoding although this may not be the most efficient selection.
  • The selected encoding is stored as a 4-bit mode indicator at the beginning of the data.

Table of encoding types for a QR code

Encoding Description 4-bit Mode Indicator
Numeric Numeric characters: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 0001
Alphanumeric Uppercase letters, numeric characters, space or one of the characters $ % * + - , / 0010
Binary Any character. 0100
Kanji Kanji characters 1000

Numeric Encoding

Numeric encoding can be used if the data is made up entirely of the characters 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9

Encoding the Data

To encode the numeric characters:

  • The digits are placed into groups of three from left to right to create values between 0 and 999.
  • The 3-digit values are coverted to 10-bit binary numbers.
  • If there is one remaining digit, it is multiplied by 16 and converted to an 8-bit binary number
  • If there are two remaining digits, 2-digit value is multiplied by 2. The result is converted to an 8-bit binary number

Example: 12345

Digit groups: 123 45

Calculation for 123

  • 123 = 0001111011 (10-bit binary value)

Calculation for 45

  • 45 × 2 = 90
  • 90 = 01011010 (8-bit binary value)

Example: 9876543

Digit groups: 987, 654 and 3

Calculation for 987

  • 987 = 1111011011 (10-bit binary value)

Calculation for 654

  • 654 = 1010001110 (10-bit binary value)

Calculation for 3

  • 3 × 16 = 48
  • 48 = 00110000 (8-bit binary value)

Alphanumeric Encoding

Alphanumeric encoding can be used if the data is made up entirely of the following:

  • Numeric digits
  • Upper case letters
  • Space
  • The characters $ % * + - , / .
Alphanumeric data values
ASCII value 0 1 2 3 4 5 6 7 8
Character 0 1 2 3 4 5 6 7 8
ASCII value 9 A B C D E F G H
Character 9 10 11 12 13 14 15 16 17
ASCII value I J K L M N O P Q
Character 18 19 20 21 22 23 24 25 26
ASCII value R S T U V W X Y Z
Character 27 28 29 30 31 32 33 34 35
ASCII value $ % * + - . / :
Character 36 37 38 39 40 41 42 43 44

Encoding the Data

To encode the alphanumeric characters:

  • Look up the value of each alphanumeric character.
  • The values are taken in pairs.
  • The first value of each pair is multiplied by 45 and added to the second value to form a value between 1 and 2024.
  • This value is then converted to an 11-bit binary number.
  • If there is one remaining character, its value is multiplied by 4 and converted to an 8-bit binary number.

Example: CAT

Character groups: CA T

Calculation for C and A

  • The values for C and A are 12 and 10
  • 45 × 12 + 10 = 550
  • 550 = 01000100110 (11-bit binary value)

Calculation for T

  • The value for T is 29
  • 4 × 29 = 29
  • 29 = 01110100 (8-bit binary value)

Binary Encoding

Binary encoding can be used for any character that has a unicode value and is stored using one of more bytes using UTF-8 encoding.

For values between 0 and 127, one byte of data is used and the character is encoded using it's ASCII value.

7-bit ASCII Values (32-127)
ASCII value 33 34 35 36 37 38 39 40 41 42 43 44
Character