USPS tracking number format
we set # as a letter
## + 9 digits + US
M + 9 digits
M + 10 digits
10 digits
20 digits
22 digits
26 digits
28 digits
30 digits
34 digits
USPS tracking number example
USPS Tracking® 9400 1000 0000 0000 0000 00
Priority Mail® 9205 5000 0000 0000 0000 00
Certified Mail® 9407 3000 0000 0000 0000 00
Collect On Delivery Hold For Pickup 9303 3000 0000 0000 0000 00
Global Express Guaranteed® 82 000 000 00
Priority Mail Express International® EC 000 000 000 US
Priority Mail Express® 9270 1000 0000 0000 0000 00 / EA 000 000 000 US
Priority Mail International® CP 000 000 000 US
Registered Mail™ 9208 8000 0000 0000 0000 00
Signature Confirmation™ 9202 1000 0000 0000 0000 00
Examples
LX542261779US
CG121737258US
CH039483967US
EH005765875US
LX590955753US
EH005962853US
CH039852503US
LM989031213US
70172400000035193417
9400111699000317735411
9200190105190925844414
42033009920019001260019524723
Ps: You can also track your USPS tracking number in trackingmore.com