Automated inventory replenishment across FBA, AWD, 3PLs and your own warehouse

Replenishment sits behind every stockout and every pallet of dead stock: when to reorder, how much, and where the units go. With one warehouse a spreadsheet can carry it. With FBA, AWD, a 3PL and your own building, it becomes a routing problem with lead times measured in months.

Why does replenishment break once stock sits in more than one place?

An FBA offer sells from stock Amazon can ship. Units at a 3PL or on your own racks are upstream supply that still has to move. A plan built on total units looks healthy until the listing goes out of stock while the 3PL holds two months of cover.

Three things usually go wrong at once:

• Lead time is treated as one number. It really stacks production, freight, receiving at the 3PL or AWD, and the inbound leg into FBA. Miss a leg and every reorder point is too low.
• Nobody owns the split. One person plans supplier POs, another plans FBA shipments.
• Capacity shows up last. FBA sets limits in cubic feet per storage type, so a plan written in units can be impossible to ship.

How do you calculate a reorder point and reorder quantity?

The reorder point is safety stock plus forecast demand during the lead time, as Oracle's inventory planning documentation defines it. Ecommerce changes what goes into each term.

Example: a SKU sells 40 units a day across channels. Production and ocean freight take 60 days and the 3PL-to-FBA leg adds 15, so lead time is 75 days and lead-time demand is 3,000 units. Add 600 units of safety stock and the reorder point is 3,600, measured against stock in every location plus open orders.

When the position crosses that line, order the gap between your target cover and the current position, rounded up to the supplier's case pack and minimum order.

Safety stock should scale with forecast error and lead-time swings, not a flat two weeks for every SKU. See safety stock and days of cover.

What does each node do in a multi-node plan?

Node	Role in the plan	What limits it	How stock moves in
FBA	Sells and ships Amazon orders	Monthly capacity limit in cubic feet per storage type; per-product blocks on excess stock	Inbound plans in Send to Amazon or the Fulfillment Inbound API
AWD	Bulk buffer that refills FBA	Eligibility and its own capacity allocation; AWD API is US only; FBA stock cannot move into AWD	Inbound orders from supplier or 3PL
3PL	Buffer stock and non-Amazon orders	Receiving time and contract terms	Transfer orders through the 3PL's API, EDI or file feed
Your warehouse	DTC, wholesale, QC and kitting	Space and labor	Supplier deliveries and internal transfers

Units waiting in AWD sit outside FBA fulfillment centers, so they are not part of FBA capacity usage, and AWD has its own capacity allocation. Amazon also names staying outside FBA storage limits as a benefit of AWD auto-replenishment, and AWD's price already covers FBA inbound placement. Auto-replenishment runs on Amazon's recommended quantity, a minimum and maximum you set, or not at all. It exists to keep FBA in stock; if the same pool also feeds Walmart Fulfillment Services or your own store, someone still decides each channel's share.

How do FBA capacity limits change the plan?

Amazon sets one FBA capacity limit per storage type each month, in cubic feet, and capacity cannot be exchanged between storage types such as standard-size and oversize. Usage counts stock already in fulfillment centers plus every shipment you have created that has not arrived. The Capacity Monitor shows usage and estimated limits for the next three months, and Capacity Manager lets you request extra space at a reservation fee you set. See FBA capacity limits.

Separately from capacity, Amazon may block new shipments for a single product whose FBA stock is well beyond normal replenishment levels, and the block applies to transfers from AWD as well. It lifts once that product's supply returns to healthy levels.

So plan in cubic feet per storage type, not units, because bulky SKUs eat capacity fast. When space is tight, rank SKUs by days of cover and margin and ship the ones closest to running out first, then schedule the next FBA shipment against next month's estimated limit.

There is a floor as well as a ceiling. In the US, eligible products pay a low-inventory-level fee when both the 30-day and 90-day historical days of supply are below 28 days, calculated per FNSKU since January 15, 2026. One exemption covers SKUs where 70% or more of the inventory was auto-replenished through AWD over the prior 90 days, so a SKU that also takes regular 3PL shipments can lose it. A buffer held at a 3PL has to keep FBA above that line on its own schedule. Overfilling FBA to dodge a stockout moves the problem into long-term storage fees.

How does Growth OS compute reorder quantities and draft POs and shipments?

Growth OS is deployed on your own accounts, so replenishment runs on your data and that data stays yours. Custom modules we build are yours; the base is licensed to you. It tracks demand and days of cover per SKU and channel, and adds channel demand together to size the supplier order. Each lead-time leg is refreshed from actual receipts, so a supplier slipping from 45 to 55 days moves the reorder point without anyone editing a sheet.

Amazon's restock recommendations, available as an SP-API report, are one input. They plan shipments into Amazon only, so a SKU where they disagree sharply with the plan gets flagged for review. The same inventory position feeds inventory-aware ad spend, so ads ease off SKUs about to run out.

On top of the base we build what your operation needs, such as an agent that reads supplier emails and updates PO dates. We have built this plumbing before: Seller7, a multi-marketplace seller OS used by 700+ sellers across 20+ marketplaces.

Where is your replenishment leaking?

The free Quick Scan in the Ops Gap Diagnostic works from the Amazon reports you upload and returns your top three operations gaps, each with a yearly dollar estimate, which can include replenishment. The paid Deep Diagnostic covers every channel. If you already know this is the gap, see how Growth OS runs replenishment alongside listings, orders, advertising and reporting.