The question behind the ratio
Across the earlier guides in this rung you learned to *count* and to *cost* what a business sells — perpetual versus periodic, FIFO versus LIFO versus weighted average, and the cost of goods sold formula that ties beginning inventory, purchases, and ending inventory together. All of that answers *how much* the goods cost. This last guide asks a different and very practical question: how fast is the inventory moving? A shelf full of stock is not a trophy. It is money the business has already spent, frozen into objects, waiting to thaw back into cash only when a customer pays. The speed of that thaw is what we are about to measure.
Why should anyone fret over speed? Because inventory is one of a company's biggest current assets, and every day it sits still it quietly eats money: storage, insurance, interest on the cash tied up, and the ever-present danger that the goods spoil, go out of fashion, or are simply marked down to clear. Stock that flies off the shelf returns that cash quickly, ready to buy more goods and earn again. Stock that lingers is a slow leak. The two ratios in this guide — [[inventory-turnover|inventory turnover]] and days sales in inventory — are just two ways of looking at that one speed.
Inventory turnover: how many times the shelf empties
Inventory turnover counts how many times, in a year, a company sells through and replaces its entire stock. The formula is deliberately plain: take the year's cost of goods sold and divide it by the *average* inventory held during the year. Picture a small wine shop whose COGS for the year was 600,000, holding on average 100,000 of bottles on its racks. Its turnover is 600,000 ÷ 100,000 = 6. The shop emptied and refilled its racks six times over the year — its stock turned over once every two months.
Two details in that formula are easy to get wrong, so hold them carefully. First, the *top* is cost of goods sold, not sales revenue. Inventory sits on the books at cost, so to compare like with like we must measure the flow out of it at cost too — using the marked-up selling price on top would inflate the ratio for no honest reason. Second, the *bottom* is *average* inventory, not the year-end figure. Because stock swells and shrinks through the seasons, the usual shortcut is to add the beginning and ending balances and halve them: (beginning + ending) ÷ 2. Using only the December 31 figure can badly mislead — a toy shop counted right after Christmas looks almost empty and would seem to turn over impossibly fast.
Days sales in inventory: the same speed, told in days
"Six times a year" is a fine answer, but most people picture time in days, not in turns. So we flip the ratio over: days sales in inventory (often called *days inventory outstanding*, or simply *days on hand*) asks how many days the average item waits on the shelf before it is sold. You get it by dividing 365 by the turnover. For the wine shop, that is 365 ÷ 6 ≈ 61 days. The very same fact — stock turning every two months — now wears a friendlier face: on average, a bottle sits for about two months between arriving and leaving.
Cost of goods sold 600,000
Inventory turnover = ------------------------- = ------- = 6 times
Average inventory 100,000
365 365
Days sales in inventory = ----------------- = ------ ~= 61 days
Inventory turnover 6
higher turnover -> fewer days on hand -> cash freed up faster
lower turnover -> more days on hand -> cash frozen longerDays on hand is the version that managers actually live by, because it speaks the language of operations. "We hold 61 days of stock" tells a buyer exactly how much runway is on the shelf and how early to reorder; "our turnover is 6" needs translating first. The two numbers carry identical information — they are the same coin seen from its two faces — so reach for whichever makes the point land. Analysts comparing companies tend to quote turnover; operators running a warehouse tend to think in days.
What fast and slow mean — and why it depends on the trade
It is tempting to say "high turnover good, low turnover bad," but that is too blunt. There is no universal right number — the only honest benchmark is the same industry. A supermarket lives on razor-thin margins and survives by sheer velocity: fresh food might turn 20 or more times a year, just a couple of weeks on hand, because milk and lettuce *must* move before they rot. A jeweller, by contrast, may turn its stock only once or twice a year and be perfectly healthy — diamonds do not spoil, each piece is dear, and a customer expects to browse a wide selection that inevitably sits a while. Judge a 2 as alarming for the grocer and entirely normal for the jeweller.
What you watch closely is not the bare level but the *trend* and the *contrast*. A turnover that drifts downward year over year, or sits well below close rivals, is a flag worth chasing. Falling turnover can mean demand is cooling and goods are piling up unsold; it can mean a buyer over-ordered; it can mean obsolete stock is clogging the shelves. But — and this is the honest caveat — climbing turnover is not automatically a triumph either. Pushed too far, it can mean the company is running so lean that it keeps running *out*: empty shelves, stock-outs, and the lost sales of customers who came, found nothing, and went to a competitor.
The quiet danger in slow-moving stock
The deepest reason to fear slow turnover is obsolescence — the risk that goods lose value while they wait. A warehouse of last season's phones, last year's fashions, or a drug nearing its expiry date may still sit on the books at full cost, yet no customer will now pay that. The longer the days-on-hand, the more of the stock is exposed to this slow rot of value. And here is the trap for a beginner: a high inventory balance can look reassuring — it *is* an asset, after all — while quietly being worth far less than its recorded number. Slow turnover is often the first visible symptom that this gap is opening.
Accounting has a guardrail for exactly this, met earlier in the rung: the [[lower-of-cost-or-market|lower of cost or market]] rule (in modern standards, lower of cost or net realizable value). It forbids a company from carrying inventory above what it can realistically fetch. When season-end jackets that cost 80 can now be cleared for only 30, the company must write the stock down and book a loss *now*, rather than pretend the asset is still worth 80. Slow turnover is the early warning; the write-down is the bill that eventually comes due. A sudden inventory write-down in the notes is very often the delayed echo of a turnover ratio that had been sliding for quarters.
There is a cash side to all this, too, and it is the side that quietly kills small businesses. Inventory soaks up working capital — cash that is now locked inside goods instead of available to pay suppliers, wages, and rent. A firm can be profitable on paper and still choke if too much of its cash is frozen in slow stock it cannot sell. This is one more face of the lesson that runs through all of accounting: profit is not cash. Squeezing the days-on-hand down — without starving the shelves into stock-outs — is one of the most direct ways a business frees up cash without borrowing a cent.
Computing it cleanly, step by step
- Pull the year's cost of goods sold from the income statement — at cost, never the sales figure.
- Find average inventory: add beginning and ending inventory from the balance sheet and divide by two (use monthly averages if the business is highly seasonal).
- Divide COGS by average inventory — that is inventory turnover, the number of times stock cycled in the year.
- Divide 365 by that turnover to get days sales in inventory — the average days an item waits on the shelf.
- Compare both against the same company's prior years and against industry peers — never against an absolute ideal, which does not exist.
One last honest wrinkle ties back to the cost-flow guides earlier in this rung. Because LIFO, FIFO, and weighted average each pin a different cost onto ending inventory and COGS, two firms identical in every real way can report different turnover ratios purely from the method they chose. Under rising prices, LIFO tends to leave a small, old-cost inventory on the balance sheet, which mechanically *inflates* the turnover ratio compared with FIFO. So when you set two companies side by side, check that they cost their inventory the same way before you trust the comparison — the ratio is only ever as solid as the numbers feeding it.