Field guide

Understand what the 65 bars actually encode.

Barcode Inspector translates the four-state USPS Intelligent Mail pattern into its numeric value, tracking fields, routing fields, and physical barcode information.

What is an Intelligent Mail barcode?

The USPS Intelligent Mail barcode, commonly called an IMb, is a 65-bar postal barcode used on letters, cards, and flats. USPS uses it to support automated mail sorting, identification, routing, and participating mail services.

Each bar has one of four possible states:

Code	Bar state	Appearance
F	Full	Extends above and below the center tracker region
A	Ascender	Extends above the tracker region
D	Descender	Extends below the tracker region
T	Tracker	Occupies only the center region

The 65 bars encode a 20-digit tracking code plus an optional routing code. The complete decoded value can contain up to 31 digits.

The tracking portion

The tracking portion always contains 20 digits. Barcode Inspector separates it into the fields below.

Field	Length	What it represents
Barcode ID	2 digits	Identifies barcode processing information, including optional endorsement-line information where applicable.
Service Type ID	3 digits	Identifies the mail class and requested services, such as address correction or other electronic service options.
Mailer ID	6 or 9 digits	Identifies the mail owner or mailing agent associated with the barcode.
Serial Number	9 or 6 digits	Provides the mailpiece-specific portion. Its length complements the Mailer ID so the two fields total 15 digits.

The routing portion

An IMb may contain no routing digits or may include 5, 9, or 11 routing digits.

Length	Routing information
0 digits	No destination routing code is encoded.
5 digits	Destination ZIP Code.
9 digits	Destination ZIP+4 Code.
11 digits	Destination ZIP+4 Code plus the two-digit delivery point.

What Barcode Inspector reports

Complete Barcode: the full decoded numeric value.
USPS Tracking Data: the 20-digit tracking portion and its component fields.
Routing Data: the optional destination routing portion and its interpretation.
Physical Barcode: the detected four-state bar representation and scan information.
Additional Data: other interpretations available for the decoded result.

Tracking code is not the same as tracking history. The IMb contains identifiers and requested-service information. Barcode Inspector decodes what is printed in the barcode; it does not retrieve USPS mailpiece scan events or delivery history.

Why a scan may fail

All 65 bars matter. A missing, merged, blurred, covered, or badly distorted bar can prevent a reliable decode. Try these corrections:

Flatten the mailpiece and keep the barcode away from glare.
Make sure both ends of the barcode are visible.
Move the camera slightly farther away to improve focus.
Use even lighting or enable the flashlight.
Try scanning a sharp photo if the live camera struggles.

Official USPS references

USPS, Intelligent Mail, and related marks belong to the United States Postal Service. Barcode Inspector is an independent application and is not affiliated with or endorsed by USPS.