Penetration rate answers a simple question: out of everyone who came into the store, how many reached this zone? It is calculated as the trips that visited a zone, category, bay or display divided by all store trips in the same period.
It is the first step of every conversion funnel and the base for pricing in-store media: its media version, opportunity to see, is the share of store trips that pass a placement's visibility area. It is also one of the metrics of the end caps performance report and of the aisle-by-aisle view in aisles direction.
Low penetration is a reach problem, not a shelf problem: if few trips get to a category, no planogram change will fix its sales. Zones with very low penetration are the blind spots of the store, often caused by dead-end aisles, shortcuts or destination categories placed at the front.
Examples from the sources: a category manager can see that 92% of trips pass the main aisle but only 9% reach a back corner (traffic article). In a store with 2,103 weekly visits, 36.75% of shoppers visited the dairy and cheese section (category management article), and in a flyer analysis 19.9% of 5,000 visits passed by the CSDs section (measuring in-store promotions).