Keep back units is a safety-stock buffer in the 3Dsellers Product Catalog. You set a number of units per sales channel, and 3Dsellers subtracts that number from your available stock before it sends the quantity to eBay, Walmart, Shopify or any other channel. With 2 kept back and 5 in stock, the channel shows 3; once only 2 units are left, the channel shows 0. It stops the last unit or two from selling on a second channel before the first channel's order has shipped. The default is 0, so nothing changes until you set it.
⭐ Keep back units works together with Up To Quantity, not instead of it. The buffer is subtracted first, then the Up To Quantity cap is applied to what is left.
In this article:
What does Keep back units do?
When you sell the same stock on several channels, the last unit can sell twice: a buyer on Amazon takes it minutes before a Walmart order for the same item ships, and the Walmart order has to be cancelled. Keep back units in 3Dsellers holds a reserve. Every time 3Dsellers pushes a quantity to a channel, it sends available stock minus the number you keep back, never less than 0. The reserve is never shown on that channel, so the channel runs out "early" and the last units stay for the orders already in progress.
You set the number per channel account, in that account's Catalog Channel Settings. It applies to every product you sync to that account.
You can override it per product with the Keep Back Qty field on the product's Inventory section.
The default is 0, which means no buffer and no change to how quantities were sent before.
Where do I set Keep back units for a channel?
The field lives in the account's Catalog Channel Settings, inside the Inventory Updates from Products Changes section. It only appears while that section is set to update the quantity on the channel.
Open Product Catalog from the left menu of 3Dsellers.
In the Product Catalog left menu, scroll to Integrations and click the gear (tooltip “Channel Settings”) at the end of the account row. You can also use Settings > Integrations > the account's page > Settings in the Multichannel Catalog column.
Under Inventory Updates from Products Changes, make sure “Update the products quantity on…” is selected. The Keep back units field shows below it, with 0 as the default.
Type the number of units to hold back. Whole numbers only: 2.7 becomes 3, and a negative number becomes 0. An empty field counts as 0.
Click Save at the bottom right. Nothing is applied until you save.
Repeat for each channel account that should keep a reserve. Each account has its own number, so you can keep 2 back on Walmart and 0 on eBay.
⚠️ If the account's Inventory Updates from Products Changes is set to “Don't update the products quantity”, the Keep back units field is hidden and no buffer applies, because 3Dsellers is not sending quantities to that channel at all.
How do I set a different buffer for one product?
A product can carry its own number that beats the channel setting on every channel it is synced to.
Open the product in the Product Catalog.
Go to the Inventory section and find Keep Back Qty. When it is empty it shows the placeholder “Channel setting”, meaning the channel's number is used.
Type the number of units to keep back for this product, then save the product (Save to Catalog).
A product override of 0 is a real value: it switches the buffer off for that product even when the channel keeps units back.
Clear the field and save to go back to the channel setting.
Products with variations have one Keep Back Qty on the parent product; every variation uses it.
How is the channel quantity calculated?
For each push, 3Dsellers works out the quantity in this order: add up the stock of all warehouses (or the bundle total), subtract the keep-back number (never below 0), then apply the listing's Up To Quantity cap if there is one.
Available stock | Keep back | Up To Quantity | Channel gets |
5 | 2 | none | 3 |
2 | 2 | none | 0 |
1 | 2 | none | 0 |
10 | 2 | 5 | 5 |
6 | 2 | 5 | 4 |
3 + 4 (two warehouses) | 2 | none | 5 |
5, channel 2, product override 0 | 0 | none | 5 |
Stock that is already oversold (a negative on-hand quantity) is sent as 0, with or without a buffer.
When does a new buffer reach my listings?
Saving a Keep back units value does not push anything by itself. The new number is used on the next quantity push for each product: the next stock change from an order, a CSV import, a bulk action or a manual edit. To apply it to every listing straight away, run Revise Listings Inventory from the Product Catalog bulk actions after saving. New listings you publish from the catalog use the buffer from the first push.
Bundles, variations, warehouses and FBA
Several warehouses: 3Dsellers adds up the warehouses first, then subtracts the buffer once. Stock of 3 + 4 with 2 kept back sends 5.
Bundles: the buffer comes off the bundle total that 3Dsellers calculates from the components, not off each component.
Variations: each variation is reduced by the buffer separately. The Keep Back Qty override is set once on the parent product and applies to all its variations.
Amazon FBA and Walmart WFS: the channel whose own warehouse holds the stock is never reduced. If your stock sits in Amazon FBA, Amazon keeps showing the full quantity while eBay and Walmart show the quantity minus the buffer.
Inventory Manager (Listing Tool) sellers: Keep back units is a Product Catalog feature. Listings whose quantity is managed by the Listing Tool's Inventory Sync are not affected.
Keep back units or Up To Quantity: which do I need?
Setting | What it does | Use it when |
Up To Quantity | Caps the maximum a channel shows. With a cap of 5 and 100 in stock, the channel shows 5. Below the cap the real quantity is sent, so it does not protect the last units. | You want to look like a smaller seller or limit exposure on one listing. |
Keep back units | Holds back a fixed reserve at the bottom. With 2 kept back the channel always shows 2 fewer and reaches 0 while you still have 2. | You share stock across channels and want to stop the last units selling twice. |
You can use both. The buffer is applied first and the cap second, so stock of 10, 2 kept back and a cap of 5 sends 5, while stock of 6 sends 4.
What Keep back units does not do
It does not change your catalog stock. The reserve stays in your on-hand quantity; only the number sent to the channel is lower.
It does not push quantities on save. A new value waits for the next stock change unless you run Revise Listings Inventory.
It does not reduce the channel that holds the stock (Amazon FBA, Walmart WFS).
It does not accept fractions or negative numbers. 2.7 becomes 3 and -3 becomes 0.
It has no per-variation field. The override is per parent product.
Troubleshooting
I can't see the Keep back units field in Channel Settings
The field only shows when Inventory Updates from Products Changes is set to “Update the products quantity on…”. Select that option and the field appears below it. If quantity updates are off for the account, 3Dsellers is not sending quantities there, so there is nothing to keep back.
I saved 2 but eBay still shows my full stock
The buffer is applied on the next quantity push, not on save. Change a product's stock, or run Revise Listings Inventory from the Product Catalog bulk actions, then check the listing. If a product has its own Keep Back Qty set to 0, that product ignores the channel buffer by design.
Amazon still shows the full quantity but eBay shows less
That is expected when your stock is in Amazon FBA. The channel whose warehouse holds the stock is never reduced; only the other channels get the buffer.
The channel shows 0 although I have units
Check the buffer size. With 2 kept back, any stock of 2 or less is sent as 0. Lower the channel number, or set Keep Back Qty to 0 on that product.
FAQ
Does Keep back units lower my inventory in 3Dsellers?
No. Keep back units only changes the quantity sent to the channel. Your catalog stock and warehouse quantities stay as they are.
Can I keep back a different number on each channel?
Yes. The setting is saved per channel account in Catalog Channel Settings, so eBay, Walmart and Shopify can each have their own number.
Does Keep back units replace Up To Quantity?
No. Up To Quantity caps the maximum; Keep back units protects the minimum. 3Dsellers applies the buffer first and the cap after, and you can use both on the same product.
What happens to my existing sellers' listings?
Nothing, until you set a number. The default is 0 on every channel and every product, which sends the same quantity as before.
Can I set the buffer on one product only?
Yes. Leave the channel at 0 and type the number in the product's Keep Back Qty field. The product override always beats the channel value, including an override of 0.