Amazon seller KPIs are the handful of ratios and counts that tell an operator whether a product is selling, whether the ads behind it pay, what Amazon keeps, how fast inventory turns, and what is left per unit after all of it. Thirteen of them cover most of the questions a seller asks in a month, and each one has a formula, a home in Amazon's reports or your own books, and a way of being misread.
Sessions. Visits to your detail page in a period. Source: Business Reports, Detail Page Sales and Traffic (sell.amazon.com describes the report and the session metrics). Misread: sessions count visits, not people, and a page with rising sessions and flat units has a conversion problem, not a traffic problem.
Unit session percentage. Units ordered divided by sessions. Amazon's own conversion metric for a listing. Source: same report. Misread: treating any single figure as a benchmark. It varies by category, price point, and whether the traffic came from ads or organic search, so compare a listing to itself over time.
Units ordered. Count of units in customer orders for the period. Source: Business Reports. Misread: ordered is not shipped and not paid. Cancellations and returns come out later, and the settlement is the figure the bank sees.
ACoS. Ad spend divided by ad-attributed sales, times 100. Amazon Ads defines it this way in its ACoS guide on advertising.amazon.com. Source: campaign reports in the ad console. Misread: a low ACoS on a campaign that cannibalizes organic sales looks efficient and is not.
TACoS. Ad spend divided by total sales, ads and organic together. Source: ad spend from the ad console, total sales from Business Reports or reconciled settlements. Misread: a falling TACoS can mean ads got efficient or organic grew for reasons unrelated to ads. Check which.
ROAS. Ad-attributed sales divided by ad spend. Amazon Ads describes it as the inverse of ACoS. Source: ad console. Misread: ROAS is a revenue ratio. A 3.0 ROAS on a 25 percent margin product loses money on every attributed sale.
Fee percentage of sales. All Amazon fees on a SKU (referral, fulfillment, storage, aged surcharges, returns processing) divided by that SKU's sales. Source: settlement reports, reconciled to the SKU; the Fee Preview report under Reports, Fulfillment, Payments in Seller Central gives the forward estimate (sell.amazon.com FBA fees guide, July 2026). Misread: using the referral rate alone. For Home and Kitchen that is 15 percent on Amazon's published schedule, and the all-in figure on a light item is usually double that.
Sell-through rate. Amazon's definition: units sold and delivered over the past 90 days divided by average sellable units in fulfillment centers over the same window. Source: FBA Inventory tool. Misread: a high rate can mean strong demand or a stockout that left the denominator empty.
Weeks of cover. Units on hand divided by average weekly units sold. Source: your inventory system and sales history. Misread: computed on last quarter's velocity going into Q4, it overstates cover by whatever the seasonal lift turns out to be.
Inventory Performance Index. Amazon's 0 to 1,000 score built from excess inventory, sell-through, stranded inventory, and in-stock rate (sell.amazon.com, "What is the FBA Inventory tool?"). Source: Inventory Performance dashboard. Misread: treating the number as the goal. The four inputs are the goal; the score follows.
Return rate. Units returned divided by units sold, by SKU. Source: FBA returns report and refund lines in settlements. Misread: counting by dollar instead of unit hides a cheap product that comes back one time in five.
Contribution per unit. Price minus referral fee, fulfillment fee, allocated storage, allocated ad spend, allocated refund cost, and FIFO landed COGS. Source: reconciled settlements joined to your cost records; Amazon holds none of the COGS. Misread: leaving out ad spend or refunds because they are not "product costs." They are costs of selling that unit.
Contribution margin by SKU. Contribution per unit divided by price, or total contribution divided by SKU revenue. Source: SKU-level profit reporting. Misread: ranking SKUs by revenue and assuming the order holds for margin. It rarely does.
Illustrative numbers. Take a stainless water bottle at $24.99, Home and Kitchen, for one month.
Unit session percentage: 380 divided by 4,000 equals 9.5 percent.
ACoS and TACoS: $1,100 divided by $3,200 equals 34.4 percent ACoS. $1,100 divided by $9,496.20 equals 11.6 percent TACoS. The gap between the two says most of this product's sales arrive without an ad click.
Fee percentage of sales: $1,424.43 plus $1,805.00 equals $3,229.43. Divided by $9,496.20, that is 34.0 percent. More than double the referral rate.
Contribution per unit: $9,496.20 minus $1,424.43 minus $1,805.00 minus $1,100.00 minus $2,432.00 minus $299.88 equals $2,434.89 for the month. Divided by 380 units, $6.41 per unit, a 25.6 percent contribution margin.
Now the ACoS misread in practice. This product's ad campaign runs at 34.4 percent ACoS against a 25.6 percent margin after ads. Strip the ads out and margin before ads is $3,534.89 on $9,496.20, or 37.2 percent, so the campaign sits below break-even on a margin basis and above it on ACoS-versus-margin-before-ads. Whether that is acceptable depends on how much of the $3,200 would have come in organically anyway, and no Amazon report answers that. A period comparison of organic units before and after the campaign launched gets closer.
Contribution margin by SKU. Sessions, conversion, and ACoS explain why a product is up or down, but contribution says whether it is worth selling at all. A seller with 200 SKUs and no margin by SKU is managing traffic to products that may be losing money on each unit.
Sales and conversion metrics sit in Business Reports. Ad metrics sit in the advertising console. Fees appear in settlement and payments reports and in the Fee Preview report. Inventory metrics live in the FBA Inventory tool and the Inventory Performance dashboard. Profit metrics do not exist in Seller Central; they require your COGS joined to the fee and sales data.
It depends on the category, price, and traffic source, and any figure quoted as a universal benchmark should be ignored. Compare a listing against its own history and against sibling SKUs in your catalog.
Crunch, the analytics AI inside ConnectBooks, reads reconciled sales, fee, ad, return, and COGS data and answers questions such as which products had better margins in other months, or what pausing ads on one product did to profit. It computes the profit KPIs above from your data. It cannot supply a COGS you never entered, and it does not change a bid or a price.
No. Track contribution by SKU monthly, TACoS and return rate weekly on the top movers, and the inventory trio (sell-through, weeks of cover, IPI) on the cadence of your reorder cycle. The rest are diagnostics you open when one of those moves.
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