Most sellers fixate on surface-level metrics—sales velocity, restock alerts, Buy Box wins. But after working with dozens of high-performing brands, we’ve learned that real profitability comes from the numbers most sellers overlook. What separates reactive sellers from top-tier operators is their attention to the metrics that drive margin, cash flow, and sustainable growth.
As our Inventory Specialist puts it: “People obsess over sales velocity and restock limits—but it’s the quiet metrics behind the scenes that often tell us whether we’re scaling profitably or bleeding money.”
Here are the three often-ignored metrics we monitor constantly for our clients—because we’ve seen firsthand the difference they make.
This is inventory you’ve already paid for—but can’t sell. Amazon splits inventory into two categories: fulfillable & unfulfillable.
Fulfillable is sellable inventory in any status (available, inbound, etc.)
Unfulfillable is inventory marked as unsellable for various reasons, including:
Why It Matters
Unfulfillable units can gradually accumulate and erode your profit margins. If you’re not reviewing them regularly, you’re losing money on inventory you’ve already invested in.
What To Do
We’ve recovered hundreds of units—and thousands in revenue—for clients just by keeping this on a weekly checklist.
After your first 39 weeks on Amazon—when storage is essentially unlimited—you’ll be subject to storage capacity limits. These limits dictate how much inventory you’re allowed to send into FBA each month, and they can significantly impact your ability to stay in stock and scale effectively.
Two key factors determine your monthly capacity:
Amazon’s IPI score measures how efficiently you manage your FBA inventory. The higher your score, the more storage you’re granted. The core drivers of your IPI include:
Sales velocity also plays a major role. Amazon prioritizes storage for sellers who move inventory efficiently. If your catalog stagnates, you’re less likely to be granted additional space—even if you’re willing to pay for it through the bidding system.
Why It Matters
A low IPI or poor sales performance leads to reduced storage limits, disrupting your supply chain and slowing sales. When that happens, you face two options: cut back on inbound inventory, potentially missing sales opportunities, or bid for additional space through Amazon’s Capacity Manager—if it’s even available.
How It Works
The upside? If that added space drives sales, you earn performance credits ($0.15 for every $1 sold), which can offset up to 100% of your fee. With strong performance, the extra storage can end up being free.
This is the ratio of: Average daily inventory volume stored ÷ Average daily shipped volume
Amazon monitors this to determine whether you’re sitting on inventory. If you’re storing significantly more than you’re shipping, expect storage utilization surcharges on top of your regular monthly storage fees.
Why It Matters
Inventory that lingers in Amazon’s fulfillment centers can quietly erode your margins—well before it’s officially labeled as “excess” or “aged.” The longer it remains unsold, the more you incur storage fees and damage your inventory performance.
What To Do
At AmpliSell, we don’t treat inventory management as backend busywork—we treat it as a growth driver. Unfulfillable inventory, storage capacity limits, and the storage utilization ratio aren’t just metrics; they’re strategic levers. When managed proactively, they unlock more FBA space, reduce unnecessary fees, and protect your margins.
If you're only responding to restock alerts, you're not managing inventory—you're falling behind it. Start tracking these often-overlooked metrics consistently. Make them part of your weekly workflow. That’s how top brands stay in stock, stay efficient, and stay ahead of whatever Amazon throws their way.
Want to tighten up your inventory strategy? Let’s connect.
