What it means
The measure is deliberately simple: divide the stock value at a point in time by the sales for the period, most often a month. Both figures should be measured on the same basis, either both at retail selling prices or both at cost, since mixing the two produces a meaningless number.
The reason it matters is cash. Every dollar tied up in stock is a dollar not available for wages, rent or growth, and stock that sits too long also runs the risk of markdowns, obsolescence and storage costs.
The other side of the argument is availability. Cutting the ratio too far leads to empty shelves and lost sales, so the aim is not the lowest possible number but the lowest number that still supports the service level customers expect.
In practice retailers use the ratio forwards as well as backwards. Planners set a target ratio for each month, then multiply next month's forecast sales by that target to decide how much stock should be in place at the start of the month, which turns the measure into a buying tool rather than a report card.
The nuance is seasonality. A toy retailer holding four months of cover in September is behaving sensibly, and the same ratio in January would be a serious problem, so the ratio should always be compared against the same month last year rather than against last month.
In practice
Real-world examples
Example 1
A fashion chain reviews its stock to sales ratio by department and finds footwear at 4.2 against a target of 2.5. The buying team cancels two forward orders and runs a promotion to clear the excess before the season change.
Example 2
A builders merchant compares its ratio to last year and sees it rise from 2.1 to 3.3. Investigation shows a bulk purchase of timber made to beat a price increase, which was a deliberate decision rather than a planning failure.
Example 3
A supermarket sets a target ratio of 0.5 for fresh produce, meaning about two weeks of cover, and 2.0 for tinned goods. Reporting the two categories separately prevents the fast moving lines from disguising slow movement elsewhere.
Think of it
Stock to sales shows how much inventory you carry relative to your sales volume.
Formula
Calculation
Stock to sales ratio = value of stock on hand at the start of the period / sales for that period. Target opening stock = forecast sales x target ratio
A homeware retailer starts March with stock valued at $840,000 at retail and records March sales of $280,000, also at retail. The stock to sales ratio = $840,000 / $280,000 = 3.0, which means three months of cover at the current rate of sale.
The chain's plan calls for a ratio of 2.0 at this point in the season, so target opening stock should have been $280,000 x 2.0 = $560,000. The excess is $840,000 - $560,000 = $280,000 of stock that is tying up cash without supporting sales.
If the retailer's gross margin is 45%, that excess stock represents $280,000 x (1 - 0.45) = $154,000 of cash at cost sitting on the shelves, which is the figure the finance director would quote when arguing for a buying freeze.Case study
Seen in the real world
The following is an illustrative and entirely fictional example. Farland Garden Centres, an invented six site chain, ran out of cash every February despite a profitable trading year. The owners assumed the problem was seasonal trading and covered the gap with an overdraft each winter.
When the fictional finance manager calculated the stock to sales ratio month by month, the pattern became obvious. The buying team ordered spring ranges in November on a supplier discount, pushing the ratio to 5.8 in December against sales that would not arrive until April. Cash left the business four months before the stock earned anything back.
Farland renegotiated payment terms so the spring order was invoiced in February, and set month by month target ratios for each category. The illustrative outcome was that peak overdraft use fell by roughly $310,000 without a single change to what the business actually sold.
Watch out
Common mistakes
- Mixing measurement bases, comparing stock valued at cost against sales at retail prices, which makes the ratio look far healthier than it is.
- Reporting a single company wide ratio when fast and slow moving categories behave completely differently and need separate targets.
- Comparing the ratio against last month in a seasonal business, when the only meaningful comparison is the same month in the previous year.
Questions
People also ask
Is a lower stock to sales ratio always better?
No, because a very low ratio usually means stockouts and lost sales, so the goal is the lowest ratio that still meets the service level customers expect.
How does it differ from stock turnover?
Stock turnover counts how many times stock is sold and replaced across a full year, while the stock to sales ratio measures cover at a point in time, usually the start of a month.
Should returns and markdowns be included?
Sales should be net of returns to avoid overstating the denominator, and markdowns should be reflected in the stock valuation so the ratio uses realistic selling values.