The inventory turnover formula tells you how fast your stock turns into sales. On its own it can't tell you which products deserve your cash or your ad budget. Here's the formula, worked examples, and the metrics that close that gap.
On this page
- What is inventory turnover?
- The inventory turnover formula
- How to calculate inventory turnover: a worked ecommerce example
- Days sales in inventory and days inventory outstanding
- Sell-through rate and days of cover
- What is a good inventory turnover ratio for ecommerce?
- Why inventory turnover alone misleads a DTC brand
- How to improve inventory turnover without killing margin
- Inventory turnover calculator: the 4 numbers you need
- Make turnover a daily number, not a year-end one
The inventory turnover formula is cost of goods sold (COGS) divided by average inventory at cost, where average inventory is beginning inventory plus ending inventory, divided by 2. The answer tells you how many times you sold through and replaced your stock in a period. A brand with $1.2m of COGS in a year and $300k of average inventory turned its stock 4.0 times, which means each dollar of stock sat on the shelf for about 91 days before it sold.
You'll also see a sales-based version, net sales divided by average inventory. Avoid it. Inventory sits on your balance sheet at cost, while sales include your markup, so dividing sales by stock mixes two different units and inflates the ratio. On a 60% gross margin, the same brand above looks like it turns 10.0 times a year instead of 4.0. That's why Investopedia, the Corporate Finance Institute and most accountants use COGS on top.
For a DTC brand, inventory is usually the biggest pile of cash in the business that isn't in the bank. But turnover looks backwards, it averages across every SKU, and a stock-out can make it look better while you lose sales. That's why this guide puts turnover next to margin and ad spend.
What is inventory turnover?
Inventory turnover, also called stock turn or the inventory turnover ratio, measures how many times a business sells and replaces its stock over a period, usually a year. Higher means stock converts to cash faster. Lower means stock is sitting, costing you storage, cash and, later, markdowns.
The inventory turnover formula
Here is the inventory turnover ratio formula and the two that sit next to it:
- Inventory turnover = COGS ÷ Average inventory at cost
- Average inventory = (Beginning inventory + Ending inventory) ÷ 2
- Days sales in inventory (DSI) = 365 ÷ Inventory turnover, or (Average inventory ÷ COGS) × days in the period
If your stock swings a lot during the year, as it does for most brands heading into Q4, average the 12 month-end balances instead of just the opening and closing ones. Whatever you pick, COGS and inventory must cover the same period.
How to calculate inventory turnover: a worked ecommerce example
Take an illustrative DTC brand with $3.0m of net sales and a 60% gross margin, so $1.2m of COGS. The numbers are made up to show the maths.
Annual inventory turnover
- Find COGS for the year: $1,200,000. Use landed product cost (unit cost plus inbound freight and duties), the same basis your books use for inventory.
- Find inventory at cost at the start and end of the year: $260,000 on 1 January and $340,000 on 31 December.
- Average them: ($260,000 + $340,000) ÷ 2 = $300,000.
- Divide: $1,200,000 ÷ $300,000 = 4.0x. The brand turned its stock 4 times.
- Convert to days: 365 ÷ 4.0 = 91 days of stock on hand, on average.
Monthly inventory turnover, and annualising it
Most founders want this monthly. In September the same brand had $100,000 of COGS, with stock at cost of $300,000 on 1 September and $320,000 on 30 September. Average inventory is $310,000, so turnover is $100,000 ÷ $310,000 = 0.32x, about 3.9x annualised, or 93 days ($310,000 ÷ $100,000 × 30). The slight slowdown is normal in September, when brands build stock for Black Friday.
If the number on your dashboard looks too good, check the top line. Net sales ÷ inventory on a 60% gross margin is 2.5 times higher than COGS ÷ inventory, for exactly the same stock.
Days sales in inventory and days inventory outstanding
Days sales in inventory (DSI), also called days inventory outstanding (DIO), turns the ratio into days: average inventory ÷ COGS × the number of days in the period, or 365 ÷ inventory turnover, as the Corporate Finance Institute sets out.
DSI is a cash number. At 91 days, about a quarter of a year's COGS sits in a warehouse instead of your bank account. Get to 61 days (6 turns) on the same $1.2m of COGS and average inventory falls from $300k to $200k, freeing $100k of cash without selling an extra unit.
Sell-through rate and days of cover
Sell-through rate formula
Sell-through rate is units sold ÷ units received × 100. Buy 1,000 units of a new colourway, sell 800 in the first 8 weeks, and sell-through is 80%, which Shopify's sell-through guide treats as strong for in-season stock. Use it for drops, seasonal buys and launches, where the question is whether the buy worked.
Days of cover (the forward-looking one)
Days of cover looks forward: units on hand ÷ average daily units sold. A best seller with 420 units left selling 45 a day has about 9 days of cover. If your supplier needs 30 days to deliver, you'll be out of stock for about 3 weeks, whatever the annual turnover says. That's the number to check before you raise budget on the ad set that sells it.
What is a good inventory turnover ratio for ecommerce?
There's no single good number. Investopedia says many businesses aim for 4 to 10 turns a year, with fashion and apparel retailers closer to 9. Walmart's fiscal 2024 filings work out at roughly 8.8x, or around 41 days of stock.
Category matters more than any average. In the U.S. Census Bureau's monthly inventories and sales report for July 2026, clothing stores held 2.11 months of sales in stock (about 5.7 turns a year on a sales basis), against 1.60 for furniture and electronics and 0.77 for food and beverage stores. These are store-based retailers, so treat them as a sense check, not a DTC target.
For DTC, consumables (supplements, coffee, pet food, refills) turn fastest because people reorder. Fashion turns slower than founders expect, because every style needs a run of sizes and the buy lands a season ahead. Durables (furniture, cookware, mattresses, jewellery) vary widely by SKU. Compare yourself with your own category and your own last 12 months.
Why the SKU-level number matters more than the blended one
A blended 4.0x can hide a hero product turning 10 times a year next to a tail of colourways turning once, and the blended number rises as the hero sells while the tail ages. Track days of cover per SKU and check the bottom 20% as often as the top. That's where cash gets stuck and a dead stock problem starts.
Why inventory turnover alone misleads a DTC brand
A high-turnover SKU can be a low-margin SKU
A $12 add-on with a 25% gross margin can turn 12 times a year because it rides along in carts, while a $90 gift set with a 70% margin turns twice. Rank by turnover and the add-on wins. Rank by gross profit per dollar of stock and the gift set wins: $2.33 back for every $1 of cost, against 33 cents.
Stock-outs inflate turnover
Turnover rewards having less stock. A best seller that was out of stock for 5 weeks carries a tiny average inventory, so its turnover looks spectacular while you lost the sales you couldn't fulfil. If a SKU's turnover jumps, check its days at zero stock first.
Turnover × margin: GMROI is the better lens
Gross margin return on investment (GMROI) puts the two together: gross profit ÷ average inventory at cost, or how many dollars of gross profit each dollar of stock earns in a year. It's also turnover × markup: GMROI = inventory turnover × (gross profit ÷ COGS). Our example brand earns $1.8m of gross profit on $300k of average stock, a GMROI of 6.0 (4.0 turns × 1.5). Investopedia cites a retail rule of thumb of 3.2 or higher.
Plot your SKUs on those two axes. Fast and high margin: scale, if days of cover can take it. Fast and thin: protect the margin. Slow and high margin: push it. Slow and thin: clear it before it becomes a write-off.
Connect it to contribution margin and ad spend
GMROI stops at gross margin. A DTC brand still pays shipping, fulfilment, payment fees and the ad spend that won the order, so the real test of a SKU is its contribution margin after marketing. A product that looks great on GMROI can still lose money if it only sells with heavy prospecting or a deep discount (see when to discount). Run the numbers through the contribution margin calculator to get your breakeven ROAS per product.
Then put stock next to spend. Two rules cover most of the money:
- Don't scale ads on a SKU with 9 days of cover. If the restock is 30 days away, extra spend buys customers you can't serve. Pull prospecting back first, keep retargeting for the stock you have, and keep the Google Shopping availability attribute accurate.
- Push overstocked, high-margin SKUs. Stock you've already paid for, with a fat margin and 120+ days of cover, is the cheapest growth you have. Move budget, homepage space and email towards it before you reorder anything else.
This is the gap StoreHero's inventory view closes. It reads your Shopify stock next to your margins and ad spend, grades every product by days of cover (stockout, low, healthy, overstocked or dead), flags ads to pull before a sell-out and overstocked high-margin lines to push, and gives reorder-by dates from your supplier lead times. See our inventory alerts post, or run the free Daily inventory actions prompt in Claude or ChatGPT.
How to improve inventory turnover without killing margin
Discounting until stock moves lifts the ratio and lowers the margin on every unit. The ways that keep the margin are mostly about buying better.
- Set reorder points and safety stock per SKU. Shopify's reorder point formula is daily sales velocity × lead time + safety stock. A SKU selling 45 a day with a 30-day lead time and 300 units of safety stock should be reordered at 1,650 units. Holding the right buffer stops stock-outs without parking months of cash.
- Clear genuinely dead stock, and leave seasonal stock alone. Christmas stock in September is early, not dead. Our dead stock guide covers how to tell the two apart and clear it without training customers to wait for sales.
- Get COGS right first. Every ratio here is only as good as the product costs behind it. Our guide to ecommerce profit margins covers what belongs in COGS.
Inventory turnover calculator: the 4 numbers you need
Pull 4 numbers for the same period: COGS (profit and loss statement), inventory at cost at the start and end (balance sheet or Shopify's inventory reports) and the days in the period. Then use the formulas above: in the example, $1.2m ÷ $300k = 4.0x and 365 ÷ 4.0 = 91 days. For days of cover per SKU you also need units on hand and average daily units sold.
Make turnover a daily number, not a year-end one
StoreHero connects your Shopify stock, product margins and Meta and Google spend, so you know which ads to pull before a sell-out and which high-margin lines to push.
Key takeaways
- Inventory turnover = COGS ÷ average inventory at cost, where average inventory = (beginning + ending) ÷ 2.
- Use COGS, not sales: sales include your markup, so a 60% gross margin brand looks 2.5 times faster than it is.
- Days sales in inventory = 365 ÷ turnover. It's the cash version: how long each dollar of stock sits before it sells.
- Turnover and DSI look back. Days of cover (units on hand ÷ daily sell rate) looks forward and should drive reorders and ad spend.
- GMROI (gross profit ÷ average inventory at cost) combines speed and margin. The fastest SKU is often not the most profitable.
- Don't scale ads on a SKU with 9 days of cover; push overstocked, high-margin lines first.
Frequently asked questions
What is a good inventory turnover ratio?
It depends on the category. Investopedia says many businesses aim for 4 to 10 turns a year, with fashion and apparel closer to 9. Consumables such as supplements or coffee should turn faster than that, while furniture, cookware and jewellery usually turn slower. Compare yourself with your own category and your own last 12 months, and look at the ratio per SKU rather than only the blended number.
What does an inventory turnover ratio of 1.5 mean?
It means you sold and replaced your average inventory 1.5 times in the period. Over a year that's about 243 days of stock on hand (365 ÷ 1.5). For most DTC categories that's slow and ties up a lot of cash, unless you sell high-value, slow-moving products such as furniture or fine jewellery.
How many times should inventory be turned over per year?
There's no universal target. Many businesses aim for 4 to 10 turns a year. Fast-moving consumables can run well above that, and durables well below it. The more useful goal is to stay in stock on your best sellers while keeping slow movers from piling up, which you track with days of cover per SKU.
Is 12 a good inventory turnover ratio?
12 turns a year means roughly 30 days of stock on hand. That's strong for most DTC brands and normal for fast-moving consumables. Check that it isn't being inflated by stock-outs, though: a product that was out of stock for weeks has a small average inventory, which pushes turnover up while you lose sales.
How do you calculate days sales in inventory?
Divide 365 by your inventory turnover ratio, or divide average inventory by cost of goods sold and multiply by the number of days in the period. A brand with $300,000 of average inventory and $1,200,000 of annual COGS has 4.0 turns and about 91 days sales in inventory.
What is a good GMROI number?
A GMROI above 1 means you sell stock for more than it costs. Investopedia cites a retail rule of thumb of 3.2 or higher, so that occupancy, staff costs and profit are covered. For a DTC brand, check the result against contribution margin as well, because GMROI stops before shipping, fulfilment and ad spend.
How do you improve days sales in inventory?
Set reorder points and safety stock per SKU, buy smaller quantities more often, bundle slow movers with best sellers, clear genuinely dead stock, and move ad spend from products about to sell out to products with deep stock and strong margins. Avoid relying on discounts, which lower DSI by giving away margin.
Sources
- Investopedia: Inventory Turnover Ratio
- Corporate Finance Institute: Inventory Turnover
- Investopedia: Days Sales of Inventory (DSI)
- Corporate Finance Institute: Days Sales in Inventory
- Wall Street Prep: Inventory Turnover Ratio
- Investopedia: Gross Margin Return on Investment (GMROI)
- IFRS Foundation: IAS 2 Inventories
- U.S. Census Bureau: Manufacturing and Trade Inventories and Sales, July 2026
- Shopify: Sell-through rate
- Shopify: Reorder point formula
- Google Merchant Center Help: Availability attribute
