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Inventory & supply chain

Inventory turnover calculator — turns, days and GMROI

Calculate inventory turnover from COGS and average inventory. Get turns, days of inventory, GMROI and the cash freed by hitting a target turn rate.

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Short answer

Inventory turnover is cost of goods sold divided by average inventory at cost. With $6,400,000 of COGS and average inventory of $1,050,000, turnover is 6.1 turns a year, or 59.9 days of inventory. Read turns against your own history and your lead times, not against a cross-industry average.

Inventory turnover counts how many times you sell and replace your stock in a period. It is the fastest read on whether working capital is moving or parked, and it converts straight into days of inventory, which is the version most operations people argue about.

Enter cost of goods sold and the inventory balances for the same period. The calculator returns turns, days of inventory, GMROI if you supply a gross margin, and the cash that would come back if you hit a target turn rate.

Both figures move together: turns up means days down. Pick the one your team already uses and stop translating between them mid-meeting.

Your numbers

$

At cost, not revenue. Using sales here inflates turns by your whole gross margin.

Average inventory basis
$
$

Same valuation basis as COGS. Treat in-transit and consignment stock consistently in both figures.

days

365 for a year, 91 for a quarter. Only used to convert turns into days of inventory.

%

Margin on the same COGS. Leave blank or set 0 to skip GMROI.

turns

The turn rate you think is achievable. Shows the inventory level and cash it implies.

Result

Inventory turnover
6.1 turns

59.9 days of inventory at 365 days in the period

Average inventory at cost$1,050,000
Days of inventory59.9 days
GMROI (gross margin per $1 of stock)$2.87
Implied revenue at that margin$9,411,765
Average inventory at 8.0 turns$800,000
Cash released by the target$250,000
Current turns6.1 turns · 60 days
Target turns8.0 turns · 46 days
Average inventory = ($980,000 + $1,120,000) ÷ 2 = $1,050,000
Turnover = $6,400,000 ÷ $1,050,000 = 6.095 turns
Days of inventory = 365 ÷ 6.095 = 59.9 days
GMROI = $3,011,765 gross margin ÷ $1,050,000 = $2.87
6.1 turns and 60 days of inventory is a working range. Hold the trend and watch fill rate as you push it higher, because the last two turns usually come out of buffer stock.

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The formula

Inventory turnover = COGS ÷ Average inventory at cost
COGS
Cost of goods sold for the period. Use cost, not revenue, so the numerator and denominator sit on the same basis.
Average inventory
Usually (opening + closing) ÷ 2 at cost. A 12-point monthly average is better if your stock is seasonal.
Days in period
Used only to convert turns into days of inventory: days ÷ turns. 365 for a year, 91 for a quarter.
Gross margin %
Optional. Drives GMROI, which measures gross margin earned per dollar of inventory carried.

Some retailers divide sales by inventory valued at retail. That variant answers a different question and produces a higher number, so never compare it to a COGS-based ratio.

Worked example

COGS for the year
$6,400,000
Opening inventory
$980,000
Closing inventory
$1,120,000
Days in period
365
Gross margin
32%
Result
6.1 turns · 59.9 days of inventory · GMROI $2.87

Average inventory is ($980,000 + $1,120,000) ÷ 2 = $1,050,000. Turnover is $6,400,000 ÷ $1,050,000 = 6.1 turns, so days of inventory is 365 ÷ 6.095 = 59.9 days. At a 32% gross margin the business earns $3,011,765 of gross profit, which is $2.87 per dollar of inventory held.

How to read your inventory turnover

A turn rate only means something next to three things: last year's rate, your supplier lead times, and your service level. Six turns with two-week lead times is comfortable. Six turns with sixteen-week ocean lead times means you are running on luck.

Turns per yearDays of inventoryWhat it usually signals
1 to 2180 to 365 daysCapital is parked. Look for dead stock and obsolete SKUs before touching buying policy.
3 to 573 to 122 daysCommon with long lead times or wide assortments. Check whether the depth is deliberate.
6 to 941 to 61 daysA comfortable band for many mid-market distributors and make-to-stock manufacturers.
10 to 1524 to 37 daysTight and disciplined. Watch fill rate — this is where stockouts start to appear.
20 or moreunder 19 daysEither genuinely lean flow, or you are firefighting shortages and expediting.
Directional only. Distributors, job shops and food businesses live in very different parts of this range.

The four things that distort the ratio

  • Sales in the numerator. Dividing revenue by inventory at cost inflates turns by the whole gross margin. On a 32% margin it overstates the ratio by roughly half.
  • A two-point average on seasonal stock. If you close the year at the seasonal low, average inventory is understated and turns look better than the year actually was.
  • One big receipt near the period end. A container landing in the last week lifts closing inventory without touching COGS, so turns drop for a reason that has nothing to do with performance.
  • Mixed-basis totals. Consignment stock, in-transit goods and WIP either belong in both figures or neither. Half-in is the most common quiet error.

Turning a turn target into an action

Going from 6.1 to 8.0 turns on $6,400,000 of COGS means average inventory falls from $1,050,000 to $800,000. That is $250,000 of cash released once, plus the carrying cost you no longer pay every year — at a 21.5% rate, about $53,750. The inventory carrying cost calculator puts a rate on your own numbers.

The reduction has to come from somewhere specific: shorter lead times, smaller order quantities, or less buffer. Check the trade-off in the safety stock calculator first, because a turn target hit by starving buffers shows up later as a fill-rate problem.

Getting average inventory without a month of exports

The arithmetic is trivial. Assembling it is not: twelve monthly inventory balances at cost, COGS on the same basis, split by warehouse and product line, with consignment and in-transit treated consistently. That is usually a saved search, an export and a pivot table.

With you ask for it in words: "inventory turns by product line for the last eight quarters, using monthly average inventory". The answer comes from your own account with the query printed underneath, so you can check the definition rather than trust it.

Frequently asked questions

How do you calculate inventory turnover?

Divide cost of goods sold for the period by average inventory at cost. Average inventory is normally opening plus closing, divided by two. For example, $6.4M of COGS against $1.05M of average inventory gives 6.1 turns. Divide the days in the period by turns to get days of inventory.

What is a good inventory turnover ratio?

There is no universal figure. A spare-parts distributor with sixteen-week imports and a fresh-food wholesaler cannot be judged on the same scale. Compare your rate to your own trend, to your lead times, and to your fill rate. A rising rate with a stable fill rate is the only combination that is unambiguously good.

Should I use COGS or sales to calculate inventory turnover?

Use COGS. Inventory sits on the balance sheet at cost, so a sales numerator mixes two bases and inflates the ratio by the gross margin. The sales-to-inventory variant exists mainly in retail, where stock is sometimes carried at retail value. If you use it, label it and never compare it with a COGS-based figure.

How do inventory turns and days of inventory relate?

They are the same number expressed two ways. Days of inventory equals days in the period divided by turns, so 6.1 turns over 365 days is 59.9 days of stock. Turns are easier to compare across periods of different length; days are easier for planners, because days compare directly against lead times.

What is GMROI and how is it different from turns?

GMROI is gross margin dollars divided by average inventory at cost, so it measures margin earned per dollar invested in stock. Turns count movement only. A line turning three times at a 50% margin returns more than one turning eight times at 6%. Use turns for flow and GMROI for assortment decisions.

Why did my turnover ratio drop after a big purchase?

Because a receipt raises inventory immediately while COGS only rises when the goods sell. A container landing in the final week of a quarter lifts closing inventory, raises the two-point average, and pushes turns down. Use a monthly average inventory series if buying is lumpy, or the ratio will report timing as performance.

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