What one unit has cost you by the time it is sitting in your warehouse ready to sell. Not what the factory charged. Everything it took to get it there.
Landed cost is the supplier invoice plus everything it took to get the goods here, divided by the units that actually travelled. It stops at your warehouse door: what the marketplace takes, what the card processor takes and what returns cost you all come afterwards, and they belong in their own stack.
Only the first one arrives as a price per unit. The rest arrive as bills for a whole shipment.
A thousand units. Supplier invoice $3,100, ocean freight and origin charges $1,180, duty $190, customs brokerage and port charges $150, marine insurance $40, inland delivery and receiving $220. Total $4,880, or $4.88 a unit.
The number on the invoice was $3.10. The number worth pricing against is $4.88. Costing against the invoice alone understates this unit by 36% before a single selling cost has been taken off it. Order 2,000 units instead and the shipment charges barely move, so they land on twice as many units: the biggest components of landed cost scale with the shipment, not with the invoice.