How to Switch 3PLs Without Dropping Orders: A Warehouse Migration Plan

Brands rarely leave a fulfillment provider over price alone. They leave after a peak season that went badly, a stock discrepancy nobody could explain, or a service level that quietly stopped being met. The decision is usually the easy part; the migration is where the damage happens, because inventory in transit is inventory that cannot ship, and a channel pointed at the wrong warehouse fails silently until customers complain.

A move can be run without a service gap. It requires treating the transfer as an operations project with a cutover plan, not as a shipping exercise.

Decide what "done" means before a pallet moves

Write down the exit criteria first: the date the last order ships from the old site, the date the first order ships from the new one, and the acceptable overlap between them. Then read your existing agreement for the terms that will shape the schedule — notice period, who pays for pick-and-load of outbound transfer freight, how long storage continues to be billed on inventory awaiting pickup, and what happens to units the outgoing provider cannot locate.

Settle the disposal path for unsellable stock in the same conversation. Damaged and expired units should not be trucked across the country to be written off at the other end.

Inventory is not portable until the data is

The single most common cause of a painful migration is a SKU master that only made sense inside the old provider's system. Before anything ships, assemble a clean item file with:

• barcodes that scan, including inner and case-level codes
• unit dimensions and weights, verified rather than inherited
• case pack and pallet configuration
• lot, expiry or serial requirements where they apply
• the bill of materials for every kit or bundle, broken to components

Then count. A full count of the inventory being transferred, agreed by both providers before it loads, gives you the only defensible baseline you will get. Every discrepancy found after the trucks leave becomes an argument between two warehouses with no shared record.

Move in waves, not overnight

A single-weekend move maximizes risk for no operational gain. Sequence it instead:

1. Slow movers first. C-class inventory can be out of position for a week without affecting order flow, and it lets the new site exercise receiving, putaway and slotting on low-stakes volume.
2. Mid-range next, once the receiving process at the new building has proven itself against real cartons and real labels.
3. Fast movers last, and briefly split across both sites so that neither location can strand you.

The overlap period is not waste. It is the insurance policy that lets you route orders back to the old site if a scan process, a rate shop or an integration behaves differently than expected under load.

Cut over the order routing last

Physical inventory moving is only half of it. The systems side has its own list, and each item on it fails in a way that is invisible from the warehouse floor:

• order routing rules and inventory feeds for every sales channel
• the returns address printed on packing slips and configured in the storefront
• marketplace and retail settings that reference a ship-from location
• rate shopping and carrier account credentials at the new site
• reporting and reconciliation access for your own team

Freeze non-critical changes during the cutover window, and keep the old integration credentials live but dormant for a week rather than deleting them on day one. Making one channel work is straightforward; keeping every channel pointed at the right pool of stock is the part that breaks, and the mechanics of that are laid out in our guide to running multiple channels through one 3PL.

The first two weeks decide the story

Reconcile daily. Compare units received at the new site against units shipped from the old site, by SKU, and chase every difference while the paperwork is still fresh. Watch pick accuracy and dock-to-ship time closely in week one — new buildings are slower before they are faster, and you want to know whether you are seeing a learning curve or a process gap.

Measure against the service levels you agreed to rather than against a general feeling that things seem better; the metrics worth holding a provider to are set out in our 3PL fulfillment KPI list. If your channel mix or catalog has changed enough that the old setup no longer fits, a migration is also the natural moment to revisit how the whole operation is structured, which is the work behind our e-commerce management service.

A migration is mostly an exercise in knowing where every unit is on any given day — the visibility problem that AIDWMS exists to solve, and the reason a cutover with it is a reconciliation instead of a search.