Fewer Than Four Thousand ThingsWide moat

Costco's most consequential decision is what it refuses to sell. Fewer than 4,000 active stock keeping units per warehouse in the core business, "significantly less than other broadline retailers"¹, against something like forty to fifty thousand at a supercentre and thirty thousand at a supermarket.

Everything follows from it. If a category gets one choice instead of twenty, the volume behind that choice is twenty times larger, which is what makes a supplier take the call and cut the price. If the item sells in pallet quantities, it never needs unpacking, shelving or facing, which is why Costco can run a 147,000 square foot box with a fraction of the labour a comparable store needs. If there are 4,000 items rather than 40,000, inventory turns about thirteen times a year² instead of eight or nine, which is why the goods are usually sold before the supplier's invoice comes due. And if the assortment is small enough to be memorised, buyers can actually know their items, which is how the quality holds at the price.

The cost of the decision is real and Costco pays it every day. A member who wants a particular brand of anything will frequently not find it. The treasure-hunt merchandising — the limited-run items that appear and vanish — is often described as a delight tactic and is really a consequence: with 4,000 slots, anything new displaces something.

Do not watch the SKU count itself, which Costco discloses only as a ceiling, but the inventory turn implied by merchandise costs and average inventory: roughly 13 times in fiscal 2025. If it slides toward ten, the assortment has widened whether or not the company says so.