Usually the Fedex tracking numbers can be 12 and 14 digits, but according to the fedex tracking number tracked in Trackingmore.com,we found a Fedex tracking number can be 10/12/15/20/22 digits.
Fedex tracking number example
780371515850
425524462818
780418498000
61299995671266910991
61290983300023480447
61290983235120607902
74890983235120791126
61290983300023492518
9261299998825473220825
Ps: You can also track your FedEx tracking number in trackingmore.com