Improving Sell-Through for inventory with 1 unit per SKU

Fulfillment by Amazon Deciphering Amazon’s inventory management
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I’m trying to improve my performance metrics, but I’m kind of stuck at fully understanding the way Amazon calculates sell-through with inventory where there might be hundreds or thousands of SKUs, but almost always only one unit sent in (used media in my case). I understand that the formula is [units shipped over the past 90 days] divided by [average number of units on hand during that time period].
Doesn’t this mean that for a book or DVD that arrives in FBA, then gets sold within 90 days, it creates a sell-through of exactly 1 divided by 1 = 1, and if the unit does not sell within these 90 days, that would be 0 dived by 1, which is zero. Assuming that there is a percentage of the inventory that doesn’t sell within 90 days, the sell-through indicator should be a number between 0 and 1 for all inventory aggregated. But my current sell-through is 1.8, and the higher this number is (2.0 makes you great, 7.0 excellent), the better. I’m not a mathematician, but if the original formula is correct, a value above 1.0 can only be achieved if you sell more units than you actually have on hand, for example 2 units sold divided by 1 unit on hand = 2.0

Clearly there is something I’m missing here. There are no further explanations I could find.

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Sell through is per 90 days.

1 unit sits in the warehouse for 90 days, then sells, 1 / (90/90) = 1 sell through rate
1 unit sits in the warehouse for 30 days, then sells, 1 / (30/90) = 3 sell through rate
180 days, 1 / (180/90) = 0.5
1 day, 1 / (1/90) = 90

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Thank you. Now I understand. It’s weird that they don’t explain it like that, given that this performance indicator is crucial.

Anyway, in the light of this, how does aged inventory that is eventually removed affect this calculation? For example. if I destroy an item after sitting in FBA unsold for 180 days, how does this appear in the calculation? After all, it never sold, but took space, which should be bad.

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Yes, that 0 will drag down your overall average for the 180 days.

The per-ASIN sell through doesn’t matter, it’s your overall metrics they use when they calculate how much space you deserve each month.

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I had to read this post a few times :sweat_smile:

[1 unit ÷ (days until sold/90) = sell-through rate]

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Ok … a New York bullet train was on a 1 hour trip to Philadelphia and made three 20 minute stops on the way. How long did the trip take and where was the train during this time?

[ Thought we would ask since you seem to have algebra skills … :wink: ]

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Depends on how close to the speed of light it went, and the readers relative speed to said light speed.