How to Calculate Inventory Turnover Ratio
Imagine two businesses with the same annual sales. One holds about two months of stock on average, the other about six. The second needs three times as much cash tied up in inventory to do the same business, uses more warehouse space, and carries more risk of products becoming obsolete. Inventory turnover is the single number that makes this difference visible, which is why both finance teams and operations managers watch it closely.
What Is Inventory Turnover?
Inventory turnover measures how many times a business sells and replaces its average inventory over a period, usually a year. The higher the turnover, the faster stock converts into revenue; the lower it is, the longer stock sits in the warehouse.
The Inventory Turnover Formula
Inventory turnover = Cost of goods sold / Average inventory
Average inventory = (Opening inventory + Closing inventory) / 2
Use cost of goods sold rather than sales revenue, because inventory is valued at cost. Using revenue would include the profit margin and make turnover look higher than it really is. For businesses with strong seasonality, averaging monthly inventory balances gives a more accurate picture than using only the opening and closing figures.
A Worked Example
A distributor starts the year with inventory of 200,000, ends it with 300,000, and records cost of goods sold of 1,500,000 for the year. Average inventory is (200,000 + 300,000) / 2 = 250,000. Inventory turnover is 1,500,000 / 250,000 = 6, meaning the business replaces its inventory about six times a year.
Days of Inventory
Converting turnover into days makes it easier to interpret:
Days of inventory = 365 / Inventory turnover
For the example above, 365 / 6 is about 61 days, so an item waits roughly two months on average between arriving and being sold. Combined with supplier payment terms and customer collection times, this figure also shows how long cash is tied up in the operating cycle.
How to Interpret the Result
There is no single good turnover figure. It varies widely by industry, product type, and business model, and a fresh food distributor cannot be compared with a manufacturer holding spare parts. The most useful comparisons are:
- Against your own history: falling turnover means inventory is growing faster than sales.
- Across product groups: a healthy overall figure can hide groups that barely move.
- Against similar businesses: compare with companies of similar size in the same industry.
Very high turnover is not always good news. If stock is kept too lean, frequent stockouts, expensive urgent orders, and lost sales follow. Turnover should always be read alongside service level and stockout rates.
Why Item-Level Analysis Matters
Overall turnover does not tell you where the problems are. Analyzing turnover by item or product group reveals the slow-moving and dead stock sitting next to fast sellers. For those items, you can run promotions, return stock to suppliers, transfer it to other locations, or stop reordering. Finding dead stock early delivers the quickest gains in both cash and space.
How to Improve Turnover Sensibly
- Update safety stock and reorder points from actual demand
- Plan purchase quantities on need rather than supplier minimums alone
- Report slow-moving and dead stock regularly and act on it
- Work with suppliers to shorten lead times
- Forecast demand with seasonality and promotions in mind
Tracking It Automatically
Calculating turnover once a year from financial statements means spotting problems late. A system that records stock movements and costs in real time can calculate turnover and days of inventory continuously by item, group, and warehouse, flag dead stock automatically, and feed those insights straight into purchasing decisions.
Frequently Asked Questions
How do you calculate inventory turnover?
Divide cost of goods sold by average inventory for the period. Average inventory is usually the average of opening and closing inventory, or of monthly balances for seasonal businesses.
Why use cost of goods sold instead of sales?
Inventory is valued at cost, so cost of goods sold keeps the comparison consistent. Using sales revenue includes the profit margin and inflates the ratio.
How do you calculate days of inventory?
Divide 365 by the inventory turnover ratio. A turnover of 6 means roughly 61 days of inventory.
What is a good inventory turnover ratio?
It depends on the industry and product type. The most meaningful comparisons are with your own history, between product groups, and with similar businesses.
Is a higher inventory turnover always better?
No. Very high turnover can indicate that stock is too lean, leading to frequent stockouts and lost sales. Read it together with service levels.
Conclusion
Inventory turnover, calculated as cost of goods sold divided by average inventory, shows how quickly stock turns into revenue. Its real value comes from tracking it by item, catching dead stock early, and using the insight in purchasing. We build inventory and purchasing systems for wholesale, manufacturing, automotive, and packaging businesses that report these indicators in real time and integrate with their existing ERP.