Then, we calculate Inventory Turnover Ratio using Formula. Inventory Turnover Ratio = Cost of Goods Sold/ Average Inventory; Inventory Turnover Ratio = $1,000,000 / $3500000; Inventory Turnover Ratio = 0.29 ; As you can see Luxurious Furniture Company turnover is .29. Calculate turnover for your firm. Most businesses calculate the turnover rate at least annually. You can calculate the rate for a shorter period of time, such as a fiscal quarter (3 months). Assume that your total number of workers is 1,000 on January 1st. By December 31 of the same year, the total is 1,200. Inventory Turnover Formula Inventory Turnover = Cost of Goods Sold / Average Inventory for the Period To get an annual number, start with the total cost of goods sold for the fiscal year, then divide that by the average inventory for the same time period.