ELI5:Why is a USPS tracking number larger than the estimated number of 'grains of sand' on the earth?
[-]Chimney_Imp 61 points 3 hours ago
It's 420 followed by the zip code then 9 then 4 digits to identify the mail class, a 9-digit mailer ID and an 8 digit package ID.
So it's actually 30 including the 420+zip but only 22 are displayed under the barcode.
http://www.endicia.com/tools-resources/harrys-hints/new-usps-tracking-barcodes
Ayyy