Inventory turnover ratio is an efficiency ratio (also known as an activity ratio). It's calculated as Cost of Goods Sold (also known as Cost of Revenue) divided by the average inventory value for that time period (beginning inventory ending inventory) / 2). It's a useful number to know for many companies, to understand how quickly they are selling their inventory and therefore how efficiently they're using an expensive asset. The higher the number, the better. A lower number means the inventory is taking a long time to sell. You get the Cost of Revenue number from the Income statement, and the inventory number from the balance sheet. Why is this NOT a useful metric for Meta, which mostly sells ads? Why is it a useful number for Lululemon (which sells athletic wear)