Stock turn calculation: how fast is your stock really selling?
In short
Stock turn is cost of goods sold divided by average stock value at cost, over the same period. Calculate it for each product line rather than the whole warehouse, then cut reorders on lines with high stock value and low turn.
- Stock turn is cost of goods sold divided by average stock value, both at cost and over the same period.
- Convert turns into days of stock to compare each line with supplier lead times.
- Calculate per product line, because a blended warehouse figure hides slow lines.
- Lines with high stock value and low turn show where cash is sitting idle.
- Use the results to cut reorder quantities on slow lines before the next purchase order goes out.
Stock turn is cost of goods sold divided by average stock value at cost. Learn which figures to use, how to convert turns into days of stock, and why a per-product-line view shows exactly where cash sits idle.
Stock turn is cost of goods sold divided by average stock value at cost, measured over the same period. Use the cost of what you sold, not its selling price, and use the average of your opening and closing stock values rather than a single count. Do that for each product line separately and you get a number you can trust, plus a clear view of which shelves are holding cash that should be working elsewhere.
A single figure for the whole warehouse hides the problem. A fast-moving line can pull the average up while a slow line quietly ties up thousands. This guide shows how to calculate stock turn, convert it to days of stock, and split it by product line so you can act on it.
The stock turn formula and what goes into it
The standard formula is: stock turn = cost of goods sold (COGS) / average stock value. Both figures must be at cost. Stock sits on the balance sheet at what you paid for it, so dividing it by sales at selling price compares two different things. The result is inflated by your margin and says more about your pricing than your stock.
Average stock is usually opening stock plus closing stock, divided by two. The period can be a year, a quarter or a month, but the COGS and the average stock must cover the same period. A common error is to mix half a year of COGS with a full year's day count, which makes stock look twice as bad as it is.
Stock turn has a companion measure: days of stock, which is average stock divided by COGS, multiplied by the days in the period. A business with COGS of 600,000 and average stock of 100,000 turns its stock six times a year, or about 61 days per turn. Most owners find days easier to feel than turns, so track both.
Same period, same basis
Check that COGS and stock are both at cost, both exclude VAT or sales tax, and both cover the same dates. Most wrong stock turn figures fail on one of these three points.
Why the whole-warehouse number misleads
Suppose a trade supplier has COGS of 600,000 a year and average stock of 100,000. The overall turn is 6, which sounds healthy. Now split it by product line (all figures illustrative):
- Fasteners and consumables: COGS 240,000, average stock 20,000, turn 12 (about 30 days)
- Core fittings: COGS 300,000, average stock 50,000, turn 6 (about 61 days)
- Specialist and bulk-bought items: COGS 60,000, average stock 30,000, turn 2 (about 183 days)
The specialist line is 30 percent of the stock value but only 10 percent of COGS. It holds 30,000 of cash for half a year per turn. The blended 6 never shows that. Per-line turn does.
How to calculate stock turn by product line
Choose the period and the product lines
Pick a period of at least a quarter, ideally twelve months, so that seasonal swings do not distort the result. Then define your product lines. Use groupings that map to buying decisions, such as supplier, category or product family, so each line has one owner who can act on the result. Between 5 and 15 lines is workable for most small and medium-sized businesses.
Pull cost of goods sold for each line
Take the cost price of every unit sold in the period, grouped by line. Use the cost recorded at the time of sale, not today's replacement cost or the invoice price. Exclude delivery charges you pass on to customers unless you also include inbound freight in the stock value. Whichever you choose, apply it to every line.
Work out average stock value at cost
Record the stock value of each line at the start of the period and at the end, then average the two. For a more reliable figure, use month-end values and average all of them. A two-point average is the weakest part of the calculation: if you ran a big promotion or took a large delivery just before the year end, the closing figure will not represent a normal month.
Divide COGS by average stock
For each line, divide COGS by average stock value. The answer is the number of times that line sold through and was replaced in the period. A result of 4 means the line turned four times, so each pound or dollar of stock was sold and replaced four times.
Convert turns into days of stock
Divide the number of days in the period by the turn figure. A turn of 12 on a yearly basis is about 30 days, and a turn of 2 is about 183 days. Compare days of stock with the supplier lead time and your reorder cycle. If a line holds 183 days of stock and its supplier delivers in two weeks, you are carrying far more than you need.
Rank the lines and find the idle cash
List lines by stock value and by turn. The lines with high stock value and low turn are where cash sits idle. Multiply the excess by the gap: if a line needs 60 days of stock but holds 183, roughly two thirds of its stock value is surplus. In the example above, that is around 20,000 that could be released.
Decide an action for each slow line
Options include stopping reorders until stock falls to target, cutting order quantities, negotiating smaller or more frequent deliveries, running a clearance, or returning stock to the supplier. Set a target turn for each line and review it monthly. Fast lines deserve attention too: a turn that is very high can mean frequent stockouts.
Getting reliable figures from your systems
The calculation is simple. The data is what makes or breaks it. You need stock valued at cost by line at regular dates, and sales recorded against the same product records. If stock sits in a spreadsheet and sales sit in an accounting package, the two rarely reconcile. Business management software that keeps inventory and sales on the same product records removes that gap, and reporting lets you pull COGS and stock value by line without rebuilding the sums every month.
Purchasing is where the result gets acted on. Once you know a line holds too much, change what you order. Reviewing open purchase orders for slow lines before they are sent, and cutting quantities to match the target days of stock, stops the problem growing while the existing stock sells down.
Do not benchmark blindly
Typical turns vary widely between industries. A grocery wholesaler and a furniture dealer should not aim for the same number. Compare each line with its own history and your own lead times first, and use industry figures only as context.
Common pitfalls to avoid
Dividing sales by stock is the most frequent mistake. It was taught in some older textbooks, but it mixes selling price with cost. Another is including obsolete or damaged stock at full value. If it cannot be sold, write it down first, or the turn will look better than the reality on the shelf.
Watch for seasonal products as well. A line that sells 70 percent of its volume in two months will show a poor turn on a month-end average taken in the off season. Use a full-year average for these lines. Finally, count your stock. A stock figure that has not been checked against the shelves is a guess, and regular cycle counts keep the denominator honest.
Using the results month to month
Calculate per-line turn monthly on a rolling twelve-month basis. That smooths seasonality and still shows trends within a quarter. Keep a one-page table: line, stock value, COGS, turn, days of stock, target days and action. Review it with whoever buys the stock. Within a few cycles you will see which lines respond to tighter ordering and which need a harder decision, and the cash released goes straight to your bank balance rather than to a shelf.
Common questions
Sources
- Inventory Turnover - Formula, Calculation & ExamplesCorporate Finance Institute · accessed 2026-11-01
- Stock Turnover Ratio: Formula, Stock Days and ExampleIAK Accountants · accessed 2026-11-01