Inventory turnover ratio & EOQ calculator

Two separate questions live in every inventory decision: how efficiently is stock already on hand moving, the inventory turnover ratio, also called stock turnover or inventory turns, and how much the next order should actually be. This answers both.

The sales-based version is easier to pull straight from a published income statement, but it's less technically accurate, it doesn't strip out gross margin, so a price change alone can move the ratio even if inventory efficiency hasn't changed at all. Use the COGS version whenever COGS is actually available.

Turnover and DIO describe how inventory has been performing. EOQ, alongside reorder point, is forward-looking , it prescribes how much to order next time and when to place that order, based on demand and the cost structure of ordering versus holding stock.

"Inventory turnover ratio," "stock turnover ratio," and "inventory turns" all refer to the identical calculation. COGS divided by average inventory. "Stock turnover" is more common in UK and retail-industry usage; "inventory turns" is the shorthand often used internally by operations teams; "merchandise turnover" shows up specifically in retail accounting. Days inventory outstanding has its own second name too: "days sales of inventory" (DSI) is just as common as DIO in practice, same 365 ÷ turnover calculation either way. None of the naming variation changes the formula or the number it produces. Worth knowing before assuming a source using different terminology is describing a different metric.

One genuine mix-up worth avoiding: "stock turnover ratio" is sometimes confused with "share turnover ratio," a completely unrelated stock-market liquidity metric (shares traded ÷ shares outstanding). Same word, different world, this page is about inventory, not equities.

EOQ isn't an arbitrary compromise, it's the specific order quantity where total ordering cost and total holding cost are exactly equal. In the example above: 17.9 orders a year × $75 ≈ $1,342 in annual ordering cost; average inventory of 335 ÷ 2 = 167.5 units × $8 ≈ $1,342 in annual holding cost. The two costs land on the same number, which is exactly why this quantity minimizes their sum. Order less, and ordering cost climbs faster than holding cost falls; order more, and the reverse happens.

At the EOQ, the cost of ordering more often and the cost of holding more stock are pulling with exactly equal force.

Perishability drives most of the spread, a grocer holding fresh product for weeks faces spoilage, so fast turnover is close to mandatory. A furniture retailer's inventory doesn't spoil, so slower turnover is a normal reflection of lower purchase frequency, not mismanagement. Whether these ranges are described as turnover, stock turns, or inventory turns in a given source, the underlying benchmark is the same.

Turnover isn't purely a measure of how well a business is run, it's also mechanically shaped by how much of the supply chain gets counted as "inventory" in the first place. A factory doing only final assembly, holding a few days of parts, can show a turnover ratio of 100 or more. Include the parts suppliers feeding that assembly line, and the same combined operation might turn over closer to 12 times a year. Trace it all the way back to raw materials (steel, resin, glass), and turnover for the full chain can fall to 4 or fewer. None of these numbers is wrong; they're measuring different amounts of the same chain. Comparing your own turnover ratio against a competitor's published figure is only a fair comparison if both numbers cover a similar scope of the supply chain, a distributor holding only finished goods and a vertically integrated manufacturer holding raw materials through finished product will show very different ratios even at identical underlying efficiency.

Reorder point assumes demand and lead time are both predictable. Safety stock is the buffer for when they're not. A supplier running a few days late, or a sudden demand spike during the reorder window, eats into safety stock instead of causing a stockout. Setting it too low leaves a business exposed to exactly the kind of variability that's common in practice; setting it too high defeats much of the purpose of calculating EOQ in the first place, since excess safety stock is just additional holding cost sitting on the shelf. A common starting point is sizing safety stock against the worst reasonably expected combination of demand spike and lead-time delay, then adjusting down over time as actual variability becomes clearer from real ordering history.

Running EOQ and turnover calculations on every single SKU with equal rigor is often more effort than the inventory justifies. ABC analysis sorts products by how much they actually matter to the business, so attention gets spent where it counts. "A" items are typically the roughly 20% of SKUs generating 70-80% of inventory value or sales. These deserve tight EOQ discipline, frequent review, and careful safety stock. "B" items sit in the middle, worth periodic review but not constant attention. "C" items are the long tail, often 50%+ of SKU count but a small fraction of value, where a simple reorder rule and infrequent review is perfectly sufficient, since the cost of over-managing them exceeds what precision actually buys.

Turnover measures how fast inventory moves; GMROI measures how much profit each dollar tied up in inventory actually generates, a genuinely different question. A product can turn over quickly but carry thin margins, generating less profit per dollar invested in stock than a slower-moving but higher-margin item. A GMROI above 1.0 means the gross margin generated exceeds the average inventory investment; well below 1.0 signals a product that's tying up more capital than the margin it returns justifies, even if the turnover ratio alone looks reasonable.

The classic EOQ formula assumes constant demand, constant lead time, and a fixed per-unit cost regardless of order size. Assumptions that don't always hold. The most common real-world exception is a supplier offering a price break at a higher order quantity: even though ordering more than the calculated EOQ increases holding cost, a large enough per-unit discount can still make the bigger order cheaper in total. Checking the total cost: purchase price plus ordering plus holding, at both the EOQ and at the discount threshold is worth doing before assuming the formula's output is automatically the cheapest option available.

Days inventory outstanding is one of the three components of the cash conversion cycle, alongside days sales outstanding and days payable outstanding: CCC = DIO + DSO − DPO. A business holding inventory for 60 days, then collecting receivables for another 45 days, while paying its own suppliers on 30-day terms, has a 75-day cash conversion cycle. 75 days between paying cash out for inventory and getting cash back in from the eventual sale. Reducing DIO shortens that cycle exactly as directly as reducing DSO does, freeing up cash without touching sales or pricing at all. DSO itself is the inverse relationship of accounts receivable turnover, the same receivables data expressed as days instead of a turnover ratio, the same distinction that separates inventory turnover from DIO.

Cash spent on inventory that hasn't sold yet is cash that's left the bank but hasn't become revenue , it draws down the same cash balance a runway calculation tracks, even though it shows up as an asset, not an expense, on the balance sheet. A business ordering well above its EOQ "to be safe" is effectively choosing to tie up more cash in inventory than the math says is necessary. Worth weighing directly against how much runway that excess inventory represents, especially for a business watching its cash position closely.

The standard EOQ and reorder point formulas assume roughly constant demand throughout the year, a simplification that breaks down for a genuinely seasonal product. A single annual EOQ calculated from full-year demand can lead to over-ordering heading into the slow season and under-ordering right before the peak, since one blended average smooths over swings that matter a great deal in practice. The more reliable approach for a seasonal business is recalculating EOQ and reorder point separately for each season using that season's own demand rate, rather than relying on a single annual figure to guide ordering decisions across a demand curve that isn't actually flat.

Calculate your own turnover and EOQ above, free, or see how inventory connects to DSO and runway.