How to use this inventory turnover calculator
Inventory turnover measures how many times you sell through your average stock in a year: annual COGS divided by average inventory value. Enter those two numbers and you get the turnover ratio, days of inventory outstanding (DIO), and months of stock on hand.
- Use COGS at your landed cost, never revenue: margin would inflate the ratio.
- Average inventory value = (starting value + ending value) ÷ 2 as a quick estimate.
- DIO is the same number flipped into days: 365 ÷ turnover.
The inventory turnover formula
Turnover = annual COGS ÷ average inventory value. Both sides use cost, so the ratio measures physical stock movement, never pricing. A ratio of 5.2 means the average dollar of stock converts to sales 5.2 times a year, so roughly 70 days pass between a unit arriving and selling.
DIO: the same number in days
Days of inventory outstanding = 365 ÷ turnover, and it is the version to manage on Amazon. Units that sit past 180 days draw aged-inventory surcharges on top of monthly storage, so a DIO drifting toward that line works as a fee forecast.
Worked example: $93,600 of COGS on $18,000 of stock
Say last year cost you $93,600 in goods sold and you held $18,000 of inventory on average. Turnover is 5.2×, DIO is 70 days, and you carry about 2.3 months of stock. Each quarter the stock turns 1.3 times: a steady, financeable cadence for a private-label SKU.
- Cut average inventory to $12,000 at the same COGS and turnover jumps to 7.8× (47 days).
- If sales slow 30% at the same stock level, DIO stretches to 100 days: reorder smaller, sooner.
- Pair with the carrying cost calculator: every extra turn shrinks the value the rate bites.
What a good turnover looks like
Turnover has no universal target because it trades against stockouts: chasing a 12× turn with a 35-day lead time is how hero SKUs go dark. Grade your ratio against lead time and margin. High-margin, slow-lead products can afford 4-6 turns; commodity products need more to earn their shelf space.
- DIO under your lead time is a stockout warning, not an efficiency win.
- DIO past 180 days means aged-inventory surcharges are already accruing.
- Recompute quarterly: Q4 velocity makes annual averages lie in both directions.
Frequently Asked Questions
What is inventory turnover?
Turnover is how many times average stock converts to sales per year: COGS ÷ average inventory. A 5.2× turnover means roughly 70 days from arrival to sale.
What is the inventory turnover formula?
Turnover = annual COGS ÷ average inventory value, both at cost. Using revenue instead of COGS inflates the ratio by your margin.
What is DIO?
Days of inventory outstanding: 365 ÷ turnover. It is the same ratio expressed as days a unit sits before selling.
What is a good inventory turnover ratio?
It depends on lead time and margin; there is no universal target. DIO under your lead time signals stockouts, and DIO past 180 days signals aged-inventory fees.
How do I find average inventory value?
Add starting and ending inventory value and divide by two. Monthly averages beat two endpoints if your stock swings with Q4.
Is higher turnover always better?
No. Past a point it just means you run out of stock. A 12× turn with a 35-day lead time leaves the listing dark between POs.
How does turnover relate to carrying cost?
Every extra turn shrinks average inventory, which shrinks carrying cost. Doubling turnover roughly halves the value your carrying rate multiplies against.
How often should I measure turnover?
Quarterly, with a trailing 12-month window. Q4 velocity distorts calendar-year numbers in both directions.