USPS Im Package Generator

What is the USPS IM Package Barcode?

The USPS Intelligent Mail Package Barcode (IMpb) is the linear barcode encoding a package's tracking number on USPS shipping labels — the one printed near the top of every Priority Mail, First-Class Package Service, and USPS Ground Advantage label. Unlike the Intelligent Mail barcode (IMb) used for letter mail, which is a 4-state height-modulated symbol, IMpb is rendered as a standard linear barcode (typically Code 128) encoding the human-readable tracking number shown above or below it.

IMpb is a USPS shipping requirement, not an optional add-on: since 2016, USPS has required all commercial package shipments to carry a compliant IMpb tracking barcode, and packages without one may not receive tracking scans or automation handling and can incur non-compliance surcharges from USPS.

Structure and data content

IMpb encodes the USPS tracking number, a 20 or 22-digit numeric string (sometimes shown with a leading service-indicator prefix) structured as:

• Application Identifier / service type prefix: identifies the mail class or service (Priority Mail, Ground Advantage, etc.).
• Mailer ID: the same USPS-assigned identifier used in Intelligent Mail letter barcodes, identifying the shipping account or business.
• Package/serial identifier: a unique sequence number for the specific package, generated by the shipper's label software or USPS-approved shipping platform.
• Check digit: a mod-10 checksum ensuring the tracking number's integrity.

Because the tracking number itself follows a defined USPS structure, the barcode is generated from a tracking number your shipping software or USPS account already produces — it's not typically composed from scratch by hand.

Technical specifications

IMpb is rendered as a Code 128 linear barcode (typically subset C for numeric-only tracking numbers), a widely supported symbology chosen specifically so existing conveyor and handheld scanners across the USPS network and partner carriers can decode it without specialized 4-state reading hardware. The encoded tracking number is 20 or 22 digits, made up of an application identifier/service-type prefix, a 6- or 9-digit Mailer ID, a package serial number, and a trailing mod-10 check digit — the same Mailer ID concept used in the letter-mail Intelligent Mail barcode, but arranged for linear encoding rather than 4-state bars. USPS's IMpb technical specification also mandates the human-readable tracking number be printed adjacent to the barcode in a defined font size for manual lookup.

Where IM Package Barcode is used

IMpb appears on essentially every USPS package shipping label used by businesses today:

• Priority Mail and Priority Mail Express labels, where the barcode enables scan events at every processing and delivery step.
• First-Class Package Service and USPS Ground Advantage (formerly Parcel Select Ground) labels for e-commerce and small business shipments.
• USPS Click-N-Ship and third-party shipping platform (Shopify, ShipStation, Pirate Ship, Endicia, etc.) generated labels, all of which embed a compliant IMpb automatically.
• Commercial-plan and negotiated-rate shippers, for whom USPS requires IMpb compliance to receive discounted rates and avoid electronic non-compliance surcharges.

Most small businesses never generate IMpb symbols manually — their shipping platform does it automatically at label creation — but this generator is useful for testing label templates, previewing layouts, or reproducing a barcode from a tracking number in systems that don't render one natively.

How to generate an IM Package Barcode in Barcode Mint

To render an IMpb symbol from a known tracking number:

• Select USPS IM Package from the barcode type list.
• Enter your USPS tracking number (or full package identifier string) exactly as issued by USPS or your shipping platform.
• Barcode Mint renders the linear barcode along with the tracking number in human-readable form beneath it.
• Adjust bar width, height, and quiet zone to match your label size and printer capability — thermal shipping label printers (4x6 formats) have their own resolution and DPI considerations.
• Export as SVG for label template integration or PNG for quick previews.
• Use Bulk CSV → ZIP/PDF to generate barcodes for a batch of tracking numbers exported from your fulfillment system, and the REST API at /barcode?type=uspsimpackage&data=... to integrate label generation into your shipping workflow.

For actual USPS shipments, tracking numbers should come from USPS or an approved shipping platform rather than being invented manually — a barcode encoding a tracking number that USPS hasn't issued and registered won't produce valid tracking scans.

Print and scan best practices

USPS package labels are scanned by high-speed conveyor and handheld scanners throughout the sortation network, so print quality directly affects tracking reliability. Print at a minimum of 203 DPI (300 DPI is safer) on thermal label stock, keep the barcode's quiet zone clear of tape, other labels, or box seams, and avoid printing over creases or curved surfaces that can distort the bars. Always verify the tracking number's human-readable text matches the barcode exactly, since a mismatch — however it occurs — undermines both automated tracking and manual lookup at a retail counter.

IM Package Barcode vs related codes

Compared to the USPS Intelligent Mail barcode (IMb) used on letters, IMpb is a linear Code 128 symbol rather than a 4-state height-modulated one, and it encodes a full package tracking number rather than routing-plus-service data — the two share the Mailer ID concept but are otherwise built for different mail classes. Compared to POSTNET or PLANET, both retired formats, IMpb is current, mandatory, and structurally unrelated, being a linear rather than height-modulated design. Compared to a generic Code 128 barcode, IMpb is technically the same underlying symbology, but with USPS-mandated data structure (Mailer ID, service prefix, serial, check digit) and placement rules that a plain Code 128 generator wouldn't enforce.

Common uses

• Priority Mail and Priority Mail Express shipping labels
• First-Class Package Service and USPS Ground Advantage e-commerce shipments
• Click-N-Ship and third-party shipping platform generated labels
• Commercial and negotiated-rate USPS shipping requiring IMpb compliance
• Fulfillment systems batch-printing package labels from a tracking number export

Frequently asked questions

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