Inventory Turnover and Days Inventory Explained
Inventory turnover converts cost of goods sold and average inventory into an operating ratio. It can help show how quickly inventory moves through a business, but the number only makes sense when the period and accounting inputs are consistent.
The standard turnover relationship
A common inventory turnover formula divides cost of goods sold by average inventory. Using COGS instead of revenue keeps the numerator closer to the cost basis used to value inventory.
Average inventory is commonly used because a single ending balance can be misleading when inventory changes substantially during the year.
Turning turnover into days
Annual turnover can be converted into an approximate days-in-inventory figure by dividing 365 by the turnover rate. Four turns per year corresponds to about 91 days of inventory on average.
The days figure is an approximation designed to make the ratio easier to interpret operationally.
Higher is not automatically better
Faster turnover can indicate efficient inventory use, but extremely low inventory can create stockouts, rush orders or lost sales. Slow turnover can signal excess inventory, but it can also reflect a business with intentionally long product cycles.
The useful benchmark depends heavily on industry, product lifecycle and service expectations.
Keep comparisons consistent
Compare the same accounting definition over equivalent periods. Seasonal businesses may need monthly or quarterly averages rather than a simple beginning-and-ending average.
Use turnover together with gross margin, sales growth and working-capital context rather than treating it as a standalone score.