There are multiple types of GTINs with GTIN-12s, GTIN-13s and GTIN-14s, being 12, 13 and 14 digits in length respectively.
GTIN-12s and GTIN-13s are made up of three parts:
Global Company Prefix Number: This unique company identifier will be between 6 digits (able to create up to 100,000 GTINs) and 9 digits long (able to create up to 100 GTINs).
Item Reference Number (IRN): This part of the GTIN specifies the item being
identified. In a GTIN-12, the combined total number of digits between your Global Company Prefix number and IRN must be 11.
Check Digit: The last digit of a barcode number is a computer check digit which makes sure the barcode is correctly composed. To generate a check digit, or understand how they are calculated, visit the Check Digit Calculator page.
GTIN-14s include an extra part at the beginning called an Indicator Digit. Ranging from 1-8, this digit indicate what packaging level the rest of the GTIN refers to. Indicator “9” is utilized only when there is additional information about weight and counts are provided (Variable Weight and Count) that need to be included.