Ask a room full of Amazon sellers what the most important metric is, and you’ll probably hear the same answer: sales rank.

For years, BSR has been the go-to number for deciding whether a product is worth buying. It estimates how well a product is selling within its category, which makes it a genuinely useful indicator of demand.

But here’s the problem.

BSR tells you what has already happened. It doesn’t tell you what’s about to happen.

If your goal is simply to find products that sell, BSR is a great place to start. If your goal is to maximise profit, inventory is usually the more important metric.

The problem with chasing BSR

Imagine two products.

Product A

Skip

Sells well, priced in

Sales rank
#1,200
FBA sellers
55
Amazon
In stock
Days of Cover
95

Demand is high — but supply meets it easily and competition is intense, so the price has little reason to move.

Product B

Buy now

Supply is thinning

Sales rank
#6,800
FBA sellers
14
Amazon
Out of stock
Days of Cover
12

The rank isn’t impressive, so most sellers skip it. Meanwhile inventory is disappearing and competition is shrinking.

Which product is more likely to see a price increase over the next two weeks? In many cases, Product B.

Demand is only half the equation

Demand

How quickly people want to buy it. This is the half almost everyone measures.

Supply

How much inventory is actually available. This is the half almost nobody measures.

Measuring only demand is like predicting house prices from how many people want to buy — without ever checking how many houses are for sale.

The best opportunities happen when demand stays strong while supply begins to disappear.

Why inventory matters more than sales rank

Sales rank can move for dozens of reasons. Inventory tells a much simpler story: when stock starts falling faster than it’s replenished, something important is happening.

  • Suppliers are out of stock
  • Manufacturers have delays
  • Sellers can’t reorder
  • Demand unexpectedly increased

Whatever the reason, shrinking supply creates pricing opportunity. Inventory doesn’t just tell you what’s selling — it tells you how much longer the current market can support today’s price.

The metric most sellers ignore: Days of Cover

Instead of simply counting units, Days of Cover estimates how long the inventory on the marketplace will last at the current sales rate.

How to read Days of Cover

90+ daysPlenty of inventory
45 daysHealthy supply
20 daysWorth monitoringRipening
Under 15 daysPotential opportunityRipe

A product with a moderate rank but ten days of cover can end up far more profitable than a product with an incredible rank and three months of stock behind it.

Think like an investor

Company A is growing fast, but its stock is already expensive because everyone knows it’s winning. Company B is quietly improving and the market hasn’t noticed yet. Which one has more upside?

Amazon products work the same way. A great sales rank usually means everyone already knows the product is popular. Inventory trends reveal what the market hasn’t priced in yet.

The four inventory signals worth watching

1

Falling Days of Cover

Inventory is being consumed faster than it’s being replaced — the clearest sign a window is opening.

2

Declining seller count

Twenty-eight sellers last week, seventeen today. Fewer competitors usually means less pricing pressure.

3

Amazon goes out of stock

When Amazon leaves the Buy Box, third-party sellers become the primary source — and gain pricing power.

4

The inventory trend itself

Direction beats the raw number. Dropping from 60 days to 15 over three weeks says far more than sitting flat at 30.

Why timing matters more than popularity

One of the biggest mistakes sellers make is assuming the best-selling products are always the best opportunities. Often they’re not.

The best opportunity isn’t the product with the highest demand. It’s the product where demand stays strong while supply quietly disappears. That’s the moment prices begin to move — and by the time most sellers notice the increase, the window has already been open for a while.

A better way to buy

Instead of asking “what has the best sales rank?”, try asking:

  • Which products are becoming harder to find?
  • Which products have fewer sellers today than last week?
  • Which products have less than two weeks of inventory remaining?
  • Which products still have healthy demand but shrinking supply?

How Ripe Banana helps

Ripe Banana was built around a simple idea: the best buying opportunities appear before the price changes, not after. So instead of scoring demand alone, it continuously watches Days of Cover, inventory trend, seller count, Amazon availability, profitability and price movement across your catalogue.

Final thoughts

Sales rank is an important metric. It just shouldn’t be the only one guiding your buying decisions. The sellers who consistently find the best opportunities don’t only ask “how well is this selling?” — they also ask “how much inventory is left?”

While everyone else is chasing demand, the biggest opportunities come from understanding supply. See both, and you stop reacting to the market — you get there first.