Inventory Turnover Ratio: How to Calculate It and What Good Looks Like
Inventory turnover ratio is cost of goods sold divided by average inventory — how many times you sell and replace your stock in a year. This guide calculates it with a worked £ example, explains days inventory outstanding as the flip side, and shows why a single blended figure hides dead stock behind fast movers, plus what to actually do about a low or high number.
Quick summary: Inventory turnover ratio is cost of goods sold divided by average inventory over the same period — it tells you how many times you sold and replaced your entire stock in that period. A turn of 6 means you cycled through your average stock six times in a year; divide 365 by that and you get days inventory outstanding, the average number of days a unit sat before it sold. There is no universal “good” number — a grocer expects a high figure and a furniture retailer a low one — and the most important thing to understand is that a single blended turnover figure lies, because your fast movers hide your dead stock inside the average.
The ratio is easy to calculate and easy to misread. Most explainer pages give you the formula and stop. The useful question is not “what is my number” but “what is my number telling me to do” — and to answer that you almost always have to break the blended figure apart. That is what the rest of this page is for.
On this page
- What the inventory turnover ratio actually measures
- The formula: COGS ÷ average inventory
- A worked £ example
- Days inventory outstanding: the same fact, in days
- What “good” looks like — and why it depends on the category
- Why a single blended turnover number lies
- How to act on a low turnover
- How to act on a high turnover
- FAQ
What the inventory turnover ratio actually measures
Inventory turnover measures velocity: how quickly stock moves through the business and turns back into cash. Every unit sitting on a shelf is money you have already spent and not yet recovered. Turnover is the count of how many times, in a period, you emptied the shelf and refilled it.
Read it as a cash metric, not a warehouse one. High turnover means your capital is doing a lot of work — the same pound is buying, selling and re-buying stock several times a year. Low turnover means the same pound is sitting still, tied up in goods that have not sold. Two businesses with identical revenue and identical margins can have wildly different cash positions purely because one turns its stock eight times and the other twice.
That is the reason the ratio matters beyond accounting. It is a leading indicator of three expensive problems: cash trapped in stock, storage and handling cost on goods that are not moving, and obsolescence risk on anything approaching the end of its shelf or fashion life. A falling turnover trend is usually the first number to move before any of those problems become visible on the shop floor.
The formula: COGS ÷ average inventory
The standard definition is cost of goods sold divided by average inventory for the same period (Investopedia — Inventory Turnover).
Inventory turnover = Cost of goods sold (COGS) ÷ Average inventory
Two details decide whether your number is honest:
Use COGS, not revenue. Some quick calculations divide sales revenue by inventory. Revenue includes your margin; inventory is held at cost. Mixing the two inflates the ratio and makes it uncomparable to anyone else’s. COGS and inventory are both at cost, so they belong together. If you only have revenue to hand, you are estimating, not measuring.
Average the inventory. Inventory at a single point in time — say, the year-end balance — can be misleading, because year-end is often when stock is deliberately run down. The usual fix is:
Average inventory = (Opening inventory + Closing inventory) ÷ 2
If your business is seasonal, the two-point average still lies, because it misses the peak you carried in the run-up to your busy period. Where you have the data, average the month-end balances across all twelve months instead. A spreadsheet rarely does this; it takes whatever two numbers are easiest to type, which is exactly how a seasonal business ends up with a turnover figure that looks fine and a warehouse that is full for five months of the year.
A worked £ example
Take a small homeware wholesaler with a single blended set of accounts for the year.
| Figure | Amount |
|---|---|
| Cost of goods sold (year) | £1,200,000 |
| Opening inventory (1 Jan) | £180,000 |
| Closing inventory (31 Dec) | £220,000 |
| Average inventory | (£180,000 + £220,000) ÷ 2 = £200,000 |
Inventory turnover = £1,200,000 ÷ £200,000 = 6.0 turns per year.
So on average this business sold and replaced its entire stock holding six times in the year. Whether that is good depends entirely on what they sell and what their competitors manage — which we will come back to. But already the figure gives you a cash lens: they are carrying £200,000 of average stock to support £1,200,000 of cost throughput. If they could lift turnover to 8 without hurting availability, they would support the same throughput on roughly £150,000 of average stock, freeing about £50,000 of cash. That £50,000 is the prize hidden inside a turnover conversation, and it is why the ratio is worth calculating properly.
Days inventory outstanding: the same fact, in days
Turns are hard to feel. “Six turns” does not land the way a number of days does. Days inventory outstanding (DIO), sometimes called days sales of inventory, converts the ratio into the average number of days a unit sits before it sells.
Days inventory outstanding = 365 ÷ Inventory turnover
For the wholesaler above: 365 ÷ 6.0 = ≈ 61 days. On average, stock sits for about two months between arriving and being sold.
DIO is the more useful figure for operational conversations because it is directly comparable to two other things you already know: your supplier lead times and your payment terms. If your DIO is 61 days, your supplier lead time is 30 days, and you pay suppliers on 30-day terms, you are financing roughly a month of stock out of your own cash before the customer’s money arrives. Turnover and DIO are the same fact stated two ways — turnover for benchmarking against peers, DIO for reasoning about cash and cover.
What “good” looks like — and why it depends on the category
There is no single good number, and any article that gives you one is misleading you. Turnover is meaningful only against the norm for what you sell.
| Type of business | Typical turnover pattern | Why |
|---|---|---|
| Grocery / fresh food | Very high (often 15+) | Perishable, thin margins, must move fast or spoil |
| Fast-moving consumer goods | High | Cheap, predictable demand, cheap to reorder |
| General wholesale / distribution | Moderate (roughly 4–8) | Broad range, mix of steady and slow lines |
| Fashion / apparel | Moderate, sharply seasonal | Blended figure hides end-of-season collapse |
| Furniture / big-ticket retail | Low (often 2–4) | High unit value, long consideration, deliberate holding |
| Industrial spares / MRO | Very low by design | Held for availability, not velocity |
The direction of “better” is not even consistent. For the grocer, higher is almost always better until it starts causing stockouts. For the industrial spares business, a low turnover is the whole point — those parts exist so a machine is never down waiting for one, and turning them fast would mean you were not holding enough.
So the honest benchmark is not an internet figure. It is your own trend over time, and where you can get it, the norm for your specific sector. A turnover that is falling quarter on quarter is a problem regardless of the absolute number. A turnover well below sector norm is a flag to investigate, not a verdict.
Why a single blended turnover number lies
This is the part most explainers skip, and it is the part that actually changes what you do.
A whole-business turnover figure is an average, and averages hide their own worst cases. A blended turnover of 6 can be made of a top tier of products turning 20 times a year and a long tail turning 0.5 times — or almost never. The fast movers, because they cycle so often, dominate the COGS numerator and pull the blended figure up. Meanwhile the dead stock sits quietly in the average inventory denominator, contributing almost nothing to sales but plenty to the cash you have tied up.
The result is a comfortable-looking number that conceals two opposite problems at once: some lines you are probably stocking out on, and some lines that have not moved in a year. The blended figure averages a stockout and a graveyard into “fine”.
The fix is to stop calculating turnover for the whole business and start calculating it by segment. The standard way to segment is ABC analysis — rank every SKU by its contribution and split the range into A (the vital few), B (the middle), and C (the trivial many) lines. Calculate turnover, and DIO, separately for each band. Now the number tells you something. Your A items should turn fast and rarely stock out; your C items are where slow-moving and dead stock hides, and where most of your trapped cash lives. A single figure cannot show you either; three figures do.
The same logic exposes the seasonal trap. A fashion retailer with a blended annual turnover of 4 might have sold most of a range at full price and be sitting on the remainder as unsellable end-of-line. Segmenting by product age — how long since first receipt — turns “turnover of 4” into “these lines turned 9 times and these have not moved in 200 days”, which is an instruction rather than a statistic.
How to act on a low turnover
A low or falling turnover is not a problem to fix directly — it is a symptom pointing at one of a few underlying causes. Work through them in order.
- Isolate where it is low. Segment first (ABC, or by product age). A low blended figure caused by genuinely slow A-items is a different problem from one caused by a pile of dead C-items. Do not act on the blend.
- Clear the dead stock deliberately. The slowest lines are usually the biggest drag on the denominator. Mark them down, bundle them, return them to suppliers where terms allow, or write them off — but decide, rather than letting them sit. The full playbook is in dead stock management. Every pound recovered from dead stock is a pound of turnover improvement that costs you nothing in availability.
- Check that you are not over-ordering. Low turnover on lines that do sell often means order quantities are too large or reorder points are set too high. Tightening those brings average inventory down without touching sales. The mechanics are in how a reorder point system works.
- Improve the forecast. Over-holding is frequently a forecasting failure dressed up as caution — you buy extra because you do not trust the number. Better demand signals let you hold less with the same service level; see demand forecasting for a small business.
The order matters. Clearing dead stock and right-sizing orders both lift turnover, but only after you have segmented — otherwise you risk cutting stock on a line that was slow this quarter for a reason that will reverse next quarter.
How to act on a high turnover
High turnover is usually good, but it has a failure mode people miss. A turnover that is unusually high for your category can mean you are running too lean — stock arrives and leaves so fast that any wobble in supply or a spike in demand tips you straight into a stockout. Turnover measures the stock that sold; it is silent about the sales you lost because the shelf was empty.
So read a high number alongside your stockout rate and your service level. If turnover is high and stockouts are rare, that is a genuinely healthy, cash-efficient operation and you leave it alone. If turnover is high and stockouts are frequent, you are starving the business of stock — the fix is more safety cover on the affected lines, not less. The point of the ratio is never to maximise it; it is to hold it at the level that supports the service you have promised on the least cash.
None of this requires a heavyweight system. It requires an accurate stock record, COGS you can pull by segment, and the ability to calculate turnover per band rather than per business — the sort of thing that fits a business too messy for spreadsheets and not ready for a full ERP. Once turnover, DIO and stockout rate live next to each other and update on their own, the metric stops being a year-end accounting curiosity and becomes a weekly steering signal.
FAQ
What is a good inventory turnover ratio?
There is no universal figure — it depends entirely on what you sell. Grocery and fast-moving goods run high (often 15+), general wholesale sits around 4 to 8, and big-ticket or spares businesses are much lower by design. The only reliable benchmarks are your own trend over time and the norm for your specific sector. A falling trend is a problem whatever the absolute number.
How do you calculate inventory turnover ratio?
Divide cost of goods sold for a period by average inventory for the same period. Average inventory is usually opening plus closing inventory divided by two, though averaging month-end balances is more accurate for seasonal businesses. Use COGS rather than sales revenue, because inventory is held at cost and mixing in your margin inflates the ratio.
What is the difference between inventory turnover and days inventory outstanding?
They are the same fact stated two ways. Turnover counts how many times you sold and replaced stock in a period; days inventory outstanding (365 ÷ turnover) converts that into the average number of days a unit sat before selling. Turnover is easier for benchmarking against peers; DIO is easier for reasoning about cash and comparing against your lead times and payment terms.
Why is my inventory turnover ratio high but I still run out of stock?
Because a blended turnover figure is an average. Your fast-moving lines cycle so often they dominate the numerator and pull the whole figure up, while slow lines sit in the average-inventory denominator. The high figure can hide both frequent stockouts on your best sellers and dead stock on your tail at the same time. Calculate turnover per segment (ABC or by product age) rather than for the whole business to see what is really happening.
Should I use revenue or COGS for the turnover calculation?
COGS. Revenue includes your gross margin, while inventory is recorded at cost, so dividing revenue by inventory overstates the ratio and makes it uncomparable to any properly calculated figure. If you genuinely only have revenue, treat the result as a rough estimate and expect it to read higher than the true number.