Amazon controls how much inventory you can store in FBA warehouses through a system that connects your Inventory Performance Index (IPI) score to storage capacity limits. If your IPI drops below specific thresholds, Amazon restricts how much new inventory you can send in — which directly impacts your ability to restock bestsellers and maintain sales velocity.

How Amazon calculates your storage capacity

Amazon assigns FBA sellers one of two limit types: volume-based limits (measured in cubic feet) or quantity-based restock limits (measured in units). Which system applies to you depends on your sales history, account age, and IPI performance.

Volume limits apply to most newer sellers and those with IPI scores below 500. Amazon tells you exactly how many cubic feet you can store across all FBA warehouses. This number appears in Seller Central under Inventory > Inventory Planning > Storage Monitor.

Restock limits apply to established sellers with consistent sales history and IPI scores at or above 500. Instead of total storage volume, Amazon calculates how many units of each ASIN you can send based on recent sales velocity and available warehouse space. These limits update weekly.

The critical difference: volume limits restrict your total footprint regardless of how fast products sell, while restock limits focus on turnover velocity for each individual SKU.

IPI score thresholds that trigger capacity changes

Your IPI score determines whether Amazon expands or restricts your storage access. The score ranges from 0 to 1,000 and updates weekly based on four factors: excess inventory percentage, FBA sell-through rate, stranded inventory percentage, and in-stock rate for popular products.

Here's what happens at each threshold:

IPI below 450: Amazon applies the most severe restrictions. You receive both reduced volume limits AND overage fees if you exceed those limits. You also lose access to certain FBA programs like Subscribe & Save and can't send inventory to products already flagged as excess.

IPI 450-499: Standard volume limits apply. You can send inventory normally but won't receive expanded capacity. Overage fees still apply if you exceed your assigned limit.

IPI 500-999: Amazon typically switches you from volume limits to restock limits and provides expanded capacity. Sellers in this range can usually send significantly more inventory, especially for fast-turning ASINs.

These thresholds aren't arbitrary suggestions — they're hard gates that change what actions you can take in Seller Central. A seller at 495 cannot create shipments for ASINs marked as excess inventory. A seller at 505 can.

What actually counts against your storage limit

Not all inventory in FBA warehouses consumes storage capacity the same way. Understanding what counts helps you make smarter decisions about what to send and when.

Inventory that counts against limits:

  • All sellable units currently stored in fulfillment centers
  • Units in transfer between warehouses (Amazon's internal moves)
  • Reserved inventory for customer orders not yet shipped
  • Unfulfillable inventory that hasn't been removed or disposed

Inventory that doesn't count:

  • Units in active customer return processing for the first 30 days
  • Inventory in shipments you've created but Amazon hasn't received yet (in-transit doesn't count until check-in)
  • Products in the removal process (once you submit a removal order)

This creates a brief window where you can technically exceed your limit: if you create shipments while under the limit, then those shipments arrive after other inventory sells through, the received units still get checked in. Amazon won't reject shipments mid-transit. However, you'll immediately trigger overage fees and won't be able to create new shipments until you're back under the limit.

How restock limits work for individual ASINs

Sellers with IPI scores at or above 500 typically see restock limits instead of a single volume cap. Each ASIN gets its own limit based on Amazon's forecast of how many units you'll sell in the next 6-8 weeks.

Amazon displays these limits in the Restock Inventory tool and on each ASIN's inventory page. The limit appears as "Max shipment quantity" when you create a shipment.

The calculation considers:

  • Historical sales velocity for that ASIN (usually last 30-90 days)
  • Current inventory level already at FBA
  • Available warehouse capacity in Amazon's network
  • Seasonal demand patterns Amazon has observed across similar products

If you have 50 units in stock and Amazon calculates you'll sell 200 in the next two months, your restock limit might show 150 units — enough to reach the forecasted demand level without significant overstorage.

These limits refresh weekly, usually Sunday nights. If a product suddenly spikes in sales, you might see the limit increase on the next refresh. If sales slow, the limit contracts.

The overage fee structure when you exceed limits

Exceeding your storage limit triggers overage fees — a separate charge on top of standard monthly storage fees. These apply per cubic foot per month, calculated daily.

Amazon assesses overage fees when your total inventory exceeds your assigned limit at any point during the month. The fee applies only to the excess portion. If your limit is 500 cubic feet and you have 600 stored, you pay overage fees on 100 cubic feet.

The overage fee rate is significantly higher than standard storage fees. While regular storage costs $0.75-$2.40 per cubic foot depending on time of year and product size tier, overage fees add an additional $10 per cubic foot per month.

This math makes overstorage expensive fast. Exceeding your limit by even 50 cubic feet costs an extra $500 per month in fees alone, regardless of whether those products sell.

Strategic responses when you're capacity-constrained

When IPI restrictions limit how much inventory you can send, you face a choice: improve your IPI score to expand capacity, or rationalize your catalog to work within current limits. The right answer depends on your catalog structure and how quickly you can move the IPI needle.

If you have 20 or fewer SKUs: Focus entirely on IPI improvement. With a small catalog, your constraint is score-based, not selection-based. Identify which of the four IPI factors is dragging your score down (check Inventory Performance dashboard in Seller Central). If excess inventory is the issue, run promotions or liquidate slow-movers aggressively. If sell-through is low, reduce restock quantities per shipment and let inventory levels run leaner. You should see score improvements within 2-4 weeks of making changes.

If you have 50+ SKUs: Run a SKU rationalization analysis before trying to fix IPI. Calculate profit per cubic foot for each ASIN using this formula: (monthly profit ÷ cubic feet per unit ÷ average inventory level). Sort by this metric. The bottom 20% of SKUs are candidates for removal or don't-restock status. Cutting underperforming SKUs frees capacity for your best sellers AND typically improves IPI since you're removing low-sell-through products. This is often faster than waiting for IPI improvements.

If you're seasonal or running promotions: Time your inventory sends strategically around the weekly limit refreshes. If you know a product will spike in the next 30 days, you may need to send inventory earlier than optimal, accept paying for a few extra weeks of storage, and rely on the following week's limit refresh to send the remainder. Don't try to send your entire promotional inventory in one shipment if it exceeds current limits — Amazon will reject it.

IPI factors you can actually control

Improving IPI requires addressing at least one of the four score components. Two are easier to fix quickly than the others.

Excess inventory percentage (fastest to improve): Amazon flags a product as excess when you have more than 90 days of supply based on current sales velocity. Remove or liquidate these units. Submit removal orders for products you won't restock. For products you want to keep selling, create Lightning Deals or use Amazon's Outlet deals to accelerate sales velocity. Many sellers see excess inventory percentage drop from 15% to under 5% within three weeks using aggressive promotions on flagged ASINs.

Stranded inventory percentage (second-fastest): Stranded inventory is any unit in FBA that doesn't have an active listing. This happens when listings get suppressed for policy violations, when you close a listing but forget to remove inventory, or when catalog errors break the connection between inventory and ASIN. Fix stranded inventory through the Fix Stranded Inventory tool in Seller Central. Most cases resolve in 24-48 hours once you relist or correct the error.

FBA sell-through rate (harder to move quickly): This measures units sold and shipped in the last 90 days divided by average units stored during that period. You can't fake velocity — you either need to sell more or store less. Reducing restock quantities helps more than running promotions here, since promotions increase both sales AND inventory levels.

In-stock rate (hardest to control): Amazon measures how often your best-selling ASINs are in stock and available. If you're capacity-constrained, you're probably already fighting stockouts, which creates a circular problem: low IPI causes capacity limits, capacity limits cause stockouts, stockouts lower IPI further. The only solution is prioritizing capacity allocation to your top 10-20% of SKUs by revenue and accepting that slower SKUs may go out of stock.

When to use Amazon's capacity expansion options

Amazon offers two ways to temporarily expand storage limits beyond what your IPI score would normally allow: Capacity Manager and monthly storage add-ons.

Capacity Manager appears in Seller Central when Amazon has excess warehouse space and wants to fill it. You can "reserve" additional storage by committing to send inventory and agreeing to higher storage fees during that reservation period. Costs vary but typically run $0.50-$1.00 per cubic foot per month above standard storage rates.

This makes sense when:

  • You're launching a new product that will turn quickly but haven't built sales history yet
  • You're preparing for a known seasonal spike (Q4, Prime Day) and need capacity 4-6 weeks in advance
  • You have a single high-margin SKU that generates enough profit to absorb the extra fees

It doesn't make sense when:

  • Your IPI is low because you're already overstocked — paying for more capacity just locks in more slow-moving inventory
  • The reserved capacity costs more than the profit margin on products you'd send
  • You could improve IPI to 500+ within 30 days through SKU rationalization

Monthly storage add-ons work similarly but commit you for a minimum of 30 days. You can't cancel mid-month, even if the inventory sells through faster than expected.

Long-term inventory architecture to avoid limit issues

Sellers who consistently maintain IPI above 500 structure their inventory operations differently than those fighting capacity restrictions every quarter.

They restock more frequently in smaller quantities. Instead of sending 12 weeks of inventory every three months, they send 4-6 weeks of inventory every 3-4 weeks. This keeps average inventory levels lower (improving sell-through rate) and reduces excess inventory risk if demand shifts.

They set automatic restock thresholds based on capacity, not just sales. If a product typically needs 200 units in stock but only has a 150-unit restock limit, they trigger restock at 75 units remaining (half the limit) rather than waiting until stock runs critically low. This prevents the scramble to send inventory right as you approach stockout.

They drop underperforming SKUs faster. A product that hasn't sold 10 units per month for 90 consecutive days gets removed, period. No "let's give it one more quarter" exceptions. Catalog bloat is the primary cause of chronic low IPI, and sellers who maintain healthy scores are ruthless about cutting dead weight.

They use FBM as a release valve. When FBA capacity is constrained, they'll fulfill slower-moving SKUs through Seller Fulfilled Prime or standard FBM rather than fight for warehouse space. This works well for products with inconsistent demand or those that don't fit standard FBA size tiers efficiently.

What changes when you cross the 500 IPI threshold

Moving from 495 to 505 IPI doesn't just incrementally improve your situation — it fundamentally changes how Amazon treats your account.

Most sellers transition from volume limits to restock limits. This means instead of managing one total capacity number across all products, you now manage individual limits per ASIN. For sellers with differentiated catalog velocity (some SKUs turn weekly, others monthly), this is massively better. You can send 500 units of a bestseller while sending only 50 units of a slower product, whereas volume limits would force you to choose between them.

You regain access to programs blocked at lower IPI scores: Subscribe & Save enrollment, Lightning Deals for products with excess inventory flags, and the ability to send inventory to new ASINs without first proving sales history.

Overage fees disappear in most cases. Sellers with restock limits rarely trigger overage fees because Amazon's limit calculation is designed to prevent overstorage by ASIN. You'd need to consistently ignore restock limits across many products simultaneously to trigger overages.

The psychological shift matters too. At 495, you're constantly calculating whether you have space for each shipment, gaming out which products to prioritize, and watching the Storage Monitor daily. At 505, you shift focus back to normal inventory planning — making decisions based on demand forecasting and profitability rather than warehouse capacity math.