ACI labels consist of thirteen lines that are read from bottom to top and are divided into the following six parts:

1. The first (bottom) line is the start label.

2. The second line is the equipment code number. "0" is used for railroad-owned equipment, "1" for privately-owned equipment, and "6" is used for non-revenue equipment.

3. Lines three, four and five are a number indicating the equipment owner, with each reporting mark given a separate number.

4. Lines six through eleven are the car number, padded with leading zeros as necessary. On locomotives,  line six indicates the type of unit and line seven the suffix number.

5. The stop label will be on line twelve.

6. The last (top) line is used for the check digit. This check digit is calculated according the following formula: multiply the first digit by 1, the second by 2, the third by 4, the fourth by 8, the fifth by 16, the sixth by 32, the seventh by 64, the eighth by 128, the ninth by 256, the tenth by 512. Add the results together and divide by 11. The remainder after the last full division by 11 (0 to 10) is the validity digit.