Stock turn indicates how quickly a retailer’s stock is sold and then reordered. A simplistic calculation is: Stock turn = Number of items sold ÷ Average stock level. For example. A retailer sells 10,000 items in a year, and on average holds 2,500 items at one time. 10,000 ÷ 2,500 = 4. Therefore the stock turn rate is 4. This means the retailer is carrying 3 months supply.