What inventory turnover measures
Inventory turnover shows how many times a business sells through and replaces its average inventory during a defined period. It connects inventory investment with the cost of goods sold (COGS), helping sellers assess whether stock is moving at a sustainable pace.
The inventory turnover formula
Inventory turnover = cost of goods sold ÷ average inventory at cost. Use the same period for COGS and average inventory, and value inventory consistently at cost rather than retail selling price.
Average inventory = (beginning inventory + ending inventory) ÷ 2. If inventory fluctuates substantially during the period, a monthly or weekly average is usually more representative than using only two endpoints.
Worked example
Suppose an ecommerce business records $48,000 of COGS over a year. Beginning inventory at cost was $10,000 and ending inventory was $14,000. Average inventory is ($10,000 + $14,000) ÷ 2 = $12,000. Inventory turnover is $48,000 ÷ $12,000 = 4.0 times for the year.
Days inventory on hand can be estimated as 365 ÷ 4.0 = 91.25 days. This is a simplified average; individual SKUs may turn much faster or slower.
Calculate turnover by SKU and channel
A store-wide ratio can hide slow-moving products. Where the data allows, calculate turnover by SKU or product category using the COGS and average inventory attributable to that group. Keep marketplace channel reporting consistent: inventory held in an FBA warehouse, a third-party warehouse and your own location should not be double-counted.
How to interpret the result
- Very low turnover: may indicate excess stock, weak demand, long lead times or products that are becoming obsolete.
- Very high turnover: can indicate efficient stock movement, but may also mean frequent stockouts, missed sales or insufficient safety stock.
- Changing turnover: compare like periods and investigate seasonality, promotions, supplier changes and shifts in product mix.
There is no universal ideal turnover ratio. Apparel, consumables, seasonal goods and durable products have different demand patterns, shelf lives and replenishment constraints. Compare against your own history and genuinely similar product categories rather than a generic target.
Common calculation mistakes
- Using sales revenue instead of COGS in the numerator.
- Using retail value instead of inventory cost in the denominator.
- Comparing a monthly COGS figure with an annual inventory average.
- Ignoring seasonality by relying only on beginning and ending balances when stock levels vary sharply.
- Including unsellable, damaged or reserved stock without defining how it is treated.
Use turnover alongside cash and margin
Fast turnover is not automatically profitable. A product may sell quickly but produce weak contribution after marketplace fees, fulfilment, advertising and returns. Review turnover together with contribution margin, stockout frequency, aged inventory and cash tied up in replenishment. Use the product profit calculator to model order economics and the free order profit tracker to record realised contribution.
Planning note
Inventory turnover is a management metric, not a substitute for an inventory valuation policy or financial statements. Apply your accounting method consistently and ask a qualified accountant about write-downs, obsolete stock and cost-of-goods-sold treatment.