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Assortment breadth

Assortment breadth is the number of different product categories, or product lines, that a store sells.

How it works

Breadth counts how many different kinds of product a store sells: plates, mugs and cutlery make a broader range than plates alone. Its counterpart is assortment depth, the amount of choice inside each category. A store becomes broader only when it opens a product category it has never carried. In the ad account, such a category starts with no sales history of its own.

In our analysis of 100 stores (June 2025 – June 2026), categories with no earlier sales accounted for 8.9% of the new items that sold in the median growing store. In the median declining store, they accounted for 1.3%. This is an observation, not proof that breadth causes growth. To choose which way to grow, read assortment breadth vs depth.

Formula

Number of product categories (product lines) the store carries

Ways to calculate

  • By product line — the textbook “product mix width”: the number of product lines a brand carries (OpenStax, Principles of Marketing).
  • By feed category — the number of different values of product_type (your own category tree) or google_product_category (Google’s taxonomy) at a chosen level (Merchant API, ProductAttributes). The deeper the level, the larger the count.

Example

Example store, not client data.

The tableware shop’s 3,000 products sit in 12 categories of its own tree, so its breadth is 12. In Google’s taxonomy at the fourth level, the same products fall into 4 categories: Dinnerware, Drinkware, Flatware and Serveware. Adding 150 frying pans opens a 13th category in the shop’s tree and a 5th, Cookware, in Google’s. Adding 150 plates leaves both counts unchanged.

Not to be confused with

  • Assortment coverage — the share of the catalogue that takes part in advertising. Breadth is what the store carries; coverage is how much of it gets shown.

Right and wrong readings

  • Wrong: “We added 300 products, so the range got broader.” Right: breadth grows only when a new category appears. In the example, 150 plates leave it at 12; only the frying pans raise it.

Sources