Stanadard 2 of 5 is a low-density numeric symbology that has been with us since the 1960s. It has been used in the photofinishing and warehouse sorting industries, as well as sequentially numbering airline tickets. The symbology is called "2 of 5" due to the fact that digits are encoded with 5 bars, 2 of which are always wide (and the remaining three are narrow). Standard 2 of 5 is a numeric symbology and its character set includes 10 digital characters (0, 1, 2, 3, 4, 5, 6, 7, 8, 9).

Standard 2 of 5 is a very simple symbology in that all encoding information is encoded in the width of the bars. The spaces in the barcode exist only to separate the bars themselves. Additionally, a bar may either be wide or narrow, a wide bar generally being 3 times as wide as a narrow bar. The exact size of the spaces is not critical, but is generally the same width as a narrow bar.

The symbology receives this name because every character is encoded with 5 bars where 2 bars are wide. Standard 2 of 5 only uses bar width to encode the data. Interleaved 2 of 5, however, uses both widths of bars and spaces.

A complete Standard 2 of 5 barcode must include a start character and a stop character. Optionally it ends with a modulo 10 check digit.

Standard 2 of 5 is a very simple and low density symbology. Its variant, Interleaved 2 of 5 (ITF25), has a slightly higher density.

Standard 2 of 5 also is known as Code25.

Industry 2 of 5 – Identical to Standard 2 of 5.
Standard 2 of 5 Mod 10 – A modulo 10 check digit is appended to the barcode message to perform checking.

A typical Standard 2 of 5 barcode has the following structure:
1. A start character
2. Message encoded
3. Optional Mod 10 check digit
4. A stop character

1. Start with the right-most digit in the message; mark the character with even and odd position.
The right-most digit has the even position.
2. Sum all digits in the odd position
3. Sum all digits in the even position, and then multiply by 3
4. Add the result 2 and result 3;
5. Divide the result of step 4 by 10, the check digit is the result equal to that 10 minus the remainder

"Industrial 2 of 5" is another name of "Standard 2 of 5", and is functionally identical to the Standard 2 of 5.