Inventory & logistics
Inventory Turnover Ratio: Calculate Turns and Days Together
Inventory turnover ratio compares period cost of goods sold with average inventory measured on a compatible cost basis. The linked days measure expresses the same relationship in time: period days divided by turnover. Treat them as two views of one calculation rather than unrelated performance claims.
Set a consistent period and cost basis
OpenStax shows turnover as cost of goods sold divided by average inventory and explains its connection to days. In this original fixture, both periods cover 90 days, costs use the same stated basis and average balances are supplied. No sales-price revenue is substituted for cost of goods sold.
The ratios describe the aggregate period. They do not prove that every individual item sold the same number of times, or that the current mix can satisfy future orders.
Calculate the original comparison
Work through both cost and time views before interpreting the larger currency figures.
Original two-period worksheet
Period A: COGS 36,000; average inventory 12,000; 90 days.
Turnover A = 36,000 ÷ 12,000 = 3 times over the period.
Days A = 90 ÷ 3 = 30.
Period B: COGS 45,000; average inventory 15,000; 90 days.
Turnover B = 45,000 ÷ 15,000 = 3; days B = 30.
Explain what changed and what did not
Both cost of goods sold and average inventory rose by the same proportion, leaving the ratio unchanged. “Sales activity is larger” and “inventory turns faster” are different conclusions. This fixture supports the same aggregate turnover and days figure in both periods.
For a separate annual teaching example, turnover of four over a 365-day year corresponds to 365 ÷ 4 = 91.25 days. Do not directly rank that annual four against the 90-day three without considering the different time base. Do not annualize a short period without stating the additional assumption.
Check undefined or misleading inputs
Average inventory of zero makes this ratio undefined under the calculation; do not report zero turnover or infinite efficiency. Negative or inconsistent balances need investigation rather than a routine performance interpretation.
Original practice explanation
“Both 90-day periods turn inventory three times, equivalent to 30 days using the stated period. Higher currency amounts in B do not change that relationship. I would check the period and cost basis before comparing another report.”
Avoid a universal good-ratio target
An appropriate level depends on the business, product mix, service requirements and data basis. The calculation alone does not recommend buying or cutting stock. A very high aggregate result can also conceal stockouts or changes in mix.
If the average inventory input is estimated from a few snapshots, document that method. The related average-inventory guide tests how endpoint sampling can miss a seasonal build; a precise division cannot repair a misleading denominator.
Questions, answered
Should I use sales revenue instead of COGS?
This stated cost-based ratio uses COGS with cost-based average inventory; mixing sales and cost bases changes the question.
Are days inventory and turnover separate calculations?
They are linked views here: period days divided by turnover gives the corresponding days measure.
Sources and examples
ResumizeAI team. Examples are fictional teaching material, not customer results. Replace sample details with your own facts.
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