License Plate Numbers in a WMS: Tracking Pallets and Cartons, Not Just SKUs

A basic inventory system knows two things about stock: what it is (the SKU) and where it is (the location). That works for a shelf of loose units. It falls apart when the same SKU sits on six pallets from three different inbound containers, with two lot codes, spread across reserve racking and a pick face.

That's the problem license plate numbers (LPNs) solve in a warehouse management system (WMS). An LPN is a unique barcode ID for a container, such as a pallet, a carton or a tote. It lets the system track the container as one unit, not just the loose quantities inside it.

SKU, location, LPN and SSCC: what each one identifies

The LPN is an internal ID, and you can think of it as the warehouse's own tracking number for a container. The SSCC is an outbound, standards-based ID that a retailer's receiving system reads. Some warehouses use the SSCC as the LPN on outbound pallets, but they do different jobs. For how the outbound side works, see GS1-128 carton labels and SSCC codes.

How an LPN moves through the warehouse

1. Receiving. Each inbound pallet or carton is scanned against the ASN or purchase order, and the WMS prints an LPN label for it. The LPN record holds the SKU, quantity, lot or expiry date, inbound reference and receipt date.
2. Putaway. The operator scans the LPN, then scans the destination location. The system now knows exactly where that container is. The operator doesn't key in item and quantity, because they come with the LPN.
3. Moves and replenishment. Moving a full pallet from reserve to a forward location is one scan of the LPN and one scan of the new location. Every unit on it moves in the system at once.
4. Picking. When a picker takes units off an LPN, the system reduces that LPN's quantity. A full-pallet pick for a wholesale order can move the whole LPN without breaking it down.
5. Packing and shipping. Outbound cartons and pallets get their own LPNs, often nested: cartons inside a pallet, so scanning the pallet LPN brings up every carton on it.

What LPNs make possible

• Lot and expiry control. The lot code lives on the LPN record, so first-expired-first-out (FEFO) picking and recalls point to specific containers instead of a whole SKU.
• Faster pallet moves. One scan moves a full pallet's contents, with no line-by-line entry.
• Receiving traceability. Any container can be traced back to its inbound shipment, which helps with supplier claims and damage disputes.
• Cleaner cycle counts. Counters confirm whole LPNs at a location, then open only the ones that don't match.
• Accurate outbound manifests. Nested LPNs give the packing list and ASN a reliable record of what's in each carton.

When LPNs are overkill

LPN tracking adds a scan and a label at every step. For a catalog of small, each-picked items stored loose in bins, tracking each bin's contents by location is often enough. Many warehouses run a hybrid: LPNs for reserve pallets and cartons, and location-level tracking for loose pick faces. The scan points that keep inventory accurate still apply either way.

Common failure modes

• Orphan LPNs. A container is emptied but its LPN is never closed, so the system still shows stock in a location that's empty.
• Partial picks that aren't recorded. Units leave a pallet without a scan, so the LPN quantity drifts from reality.
• Duplicate labels. A label is reprinted and both copies stay in circulation. Reprint should void the old ID.
• Broken nesting. Cartons move to a different pallet physically, but the system still has them on the original one.

Each of these is a process problem more than a software one. The fix is scan discipline and exception reports that surface LPNs with zero quantity, no recent activity, or a location that doesn't match the last scan.

Questions to ask a 3PL about LPN tracking

• Do you assign LPNs at receiving, and what's recorded on each one?
• Can I see inventory by LPN and by lot, not just by SKU total?
• How are partially picked pallets handled?
• Do outbound pallets carry nested LPNs or SSCCs for retail shipments?

IDCEA's warehouse technology includes a warehouse management system, a terminal for printing and scanning SKU, pallet and location labels, and order operations software. If you're evaluating whether your current system can track inventory at the container level, we can walk through how your inbound and outbound flows would map to it.