---
title: Why are some sizes of a product not generating demand, even though a few units were sold last week?
description: Why are some sizes of a product not generating demand, even though a few units were sold last week?
---
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# Why are some sizes of a product not generating demand, even though a few units were sold last week?
Nextail calculates demand at the **product level**, taking into account average sales over the past 7, 14, and 21 days, along with other variables. This product-level demand is then broken down into **SKU-store level demand** using size curves.
Size curves are calculated at the **Store → Family → Size Set** level based on historical sales. Therefore, even if a particular size (e.g., Size L) sold a few units last week, Nextail may not propose replenishment for that size if its weight in that store is very low.
By focusing on the true buying behavior at the store-family-size set level, Nextail ensures that each store receives the right mix of sizes based on long-term trends, rather than reacting to short-term sales fluctuations.
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