How to sync stock between eBay and Amazon
By the Seller Copilot team · · 6 min read
To sync stock between eBay and Amazon, hold one stock figure per SKU in a tool connected to both. Every sale then reduces that shared number and updates the quantity on both listings, so the last unit can't sell twice. You match listings by SKU, set the sync running, and reconcile any SKUs that don't line up.
1. Match your listings by SKU
A sync links two listings only when they share a SKU. Before anything else, make sure the same product carries the same SKU on eBay and Amazon — or map both listing SKUs to one stock item. This is the step people skip, and it's why their "sync" quietly does nothing for half their range.
2. Set one stock figure per SKU
Decide the real, physical quantity you hold for each SKU and set it once, in one place. Both the eBay and Amazon quantities should be a reflection of that single number, not separate figures you keep in your head. Keep Amazon FBA stock out of this figure — it's fulfilled by Amazon and can't ship to an eBay buyer.
3. Turn on two-way sync
With SKUs matched and a shared figure in place, switch on the sync in both directions. A sale on Amazon drops the shared number and pushes the new quantity to eBay; a sale on eBay does the same for Amazon. The important part is that it fires on each sale, not on a timer — the delay in an hourly export is exactly the window an oversell slips through.
Common problems and fixes
- Half your listings never update. Almost always mismatched SKUs. Export both catalogues and line up the SKUs, or map them.
- Stock shows available that you've already sent to FBA. Your FBA stock is being counted as sellable. Separate FBA from self-held stock.
- Occasional oversells despite syncing. The sync is on a schedule, not per-sale. Two orders inside the interval both take the last unit. Move to a per-sale trigger.
FAQs
How fast does stock need to sync to prevent overselling? +
Fast enough that two near-simultaneous sales can't both take the last unit. In practice that means a near-real-time sync triggered by each sale, not an hourly export. The gap between a sale and the quantity dropping on the other channel is where overselling happens.
What if the same product has different SKUs on eBay and Amazon? +
They won't link until they share a SKU. Either align the SKUs on the listings, or map the two listing SKUs to one stock item so both draw from the same figure. Until they're mapped, each listing tracks its own stock and they'll drift apart.
Does Amazon FBA stock sync the same way? +
No — keep FBA and self-held stock separate. Amazon fulfils FBA orders from its own warehouses, so that stock isn't available to sell on eBay. Only your self-held (FBM) stock should feed the shared figure that eBay draws from.
Can I do this with a spreadsheet? +
For a handful of SKUs and low volume, briefly. It breaks the moment two orders land close together, because a spreadsheet can't reduce the number the instant a sale happens. A tool that listens for each sale is what actually prevents the oversell.
Seller Copilot does this across eBay, Amazon and your other channels — one stock figure per SKU, synced on each sale. It's on the free plan. Start free.