Inventory Turnover: Formula, Calculator and Benchmarks
Inventory turnover tells you how many times you sell and replace your stock over a period — a core measure of how hard your working capital is working. This guide explains the inventory turnover formula, walks through a worked example, gives you a fill-in calculator table you can complete with your own numbers, and shows how to read benchmarks sensibly rather than chasing a single “good” figure. Copy the calculation table below and drop in your cost of goods sold and average inventory.
The inventory turnover formula
The standard formula is:
Inventory turnover = Cost of goods sold (COGS) ÷ Average inventory
Where average inventory = (opening inventory + closing inventory) ÷ 2, both measured at cost. COGS and inventory must be on the same basis — use cost, not retail price, for both. Some businesses substitute net sales for COGS, but that mixes retail value with cost value and inflates the ratio, so cost-based is the more reliable measure. Choose a consistent period — usually a year, but a quarter or month works if your business is seasonal — and annualise if you want to compare like with like.
Days sales of inventory (the companion metric)
Turnover is easier to feel as a number of days. Days sales of inventory (DSI) = 365 ÷ inventory turnover (use the number of days in your period). A turnover of 6 means you hold roughly 61 days of stock; a turnover of 12 means about 30 days. DSI is often more intuitive for planning because it answers “how long would current stock last at this rate of sale?” Report both: turnover for the headline, DSI for the operational conversation.
Worked example
These figures are illustrative. Bright Retail’s cost of goods sold for the year is S$1,200,000. Opening inventory at cost was S$180,000 and closing inventory was S$220,000, so average inventory is (180,000 + 220,000) ÷ 2 = S$200,000. Inventory turnover is 1,200,000 ÷ 200,000 = 6.0 times a year. Days sales of inventory is 365 ÷ 6.0 = about 61 days. In plain terms, Bright Retail sells through its entire stock roughly six times a year and holds about two months of cover. Whether that is healthy depends on its sector, supplier lead times and how much safety stock its demand variability justifies.
Calculate yours: a fill-in table
Copy this table and complete the right-hand column with your own figures. Follow the steps in order; the last two rows are your results.
| Step | Input / calculation | Your figure |
|---|---|---|
| 1. Cost of goods sold (period) | From your P&L, at cost | [S$ ________] |
| 2. Opening inventory (at cost) | Value at start of period | [S$ ________] |
| 3. Closing inventory (at cost) | Value at end of period | [S$ ________] |
| 4. Average inventory | (Step 2 + Step 3) ÷ 2 | [S$ ________] |
| 5. Inventory turnover | Step 1 ÷ Step 4 | [____ times] |
| 6. Days in period | 365 for a year, 90 for a quarter | [____ days] |
| 7. Days sales of inventory (DSI) | Step 6 ÷ Step 5 | [____ days] |
How to read benchmarks sensibly
There is no universal “good” turnover, and quoted benchmarks vary widely by sector and by how they were measured, so treat any single number with caution unless you know its source and basis. As general guidance: fast-moving, low-margin categories such as groceries and fashion basics tend to turn stock many times a year, while high-value or slow-moving categories such as furniture, machinery or jewellery turn far fewer times and still trade profitably. What matters more than an industry average is your own trend and the trade-off behind it. A rising turnover frees cash and cuts obsolescence risk, but pushed too far it causes stockouts and lost sales; a falling turnover may signal overbuying, weak demand or ageing stock. Compare yourself to your own past periods and to close competitors on the same basis rather than to a headline figure of unknown origin.
Turnover by SKU, not just overall
A single company-wide ratio hides the items that matter. Calculate turnover at SKU or category level and you will usually find a familiar pattern: a small share of SKUs drives most of your sales and turns quickly, while a long tail sits for months tying up cash and shelf space. Ranking SKUs by turnover (or by DSI) is how you decide what to reorder aggressively, what to discount and clear, and what to stop stocking. This is far more actionable than the aggregate number, which can look healthy while slow movers quietly accumulate.
Common mistakes to avoid
- Mixing cost and retail values. Using sales in the numerator and cost inventory in the denominator inflates the ratio; keep both at cost.
- Using a single point-in-time inventory. A snapshot on one date can be unusually high or low; average opening and closing, or better, average several points.
- Ignoring seasonality. Measuring across a peak or trough distorts the picture; annualise or compare the same season year on year.
- Chasing a benchmark blindly. Maximising turnover without watching stockouts trades lost sales for a prettier ratio.
- Only looking at the total. The aggregate can mask dead stock; always drill to SKU level.
How WhiteBox helps
WhiteBox calculates inventory turnover and days sales of inventory from your real transactions, at overall, category and SKU level, so you can see your fast movers and dead stock without exporting to a spreadsheet. Reorder points and forecasting then act on those numbers, helping you lift turnover without stocking out. Explore our inventory features, see pricing, or get in touch.
Frequently asked questions
What is the inventory turnover formula? Inventory turnover equals cost of goods sold divided by average inventory, where average inventory is opening plus closing inventory divided by two, both measured at cost.
Should I use sales or COGS in the formula? Use cost of goods sold. Substituting net sales mixes retail value with cost value and inflates the ratio, making it hard to compare or trust.
What is a good inventory turnover ratio? It depends heavily on your sector and how the benchmark was measured. Fast-moving categories turn many times a year; high-value slow movers turn few times and still profit. Compare to your own trend and close competitors.
How is days sales of inventory related to turnover? DSI equals the number of days in your period divided by turnover. A turnover of 6 over a year is about 61 days of stock; it is often the more intuitive figure for planning.
Why calculate turnover by SKU? The company-wide ratio can look healthy while a long tail of slow movers ties up cash. SKU-level turnover shows exactly what to reorder, discount or drop.
Related reading: Inventory Management Guide (pillar), Stock Card and Bin Card Templates, Inventory Audit Checklist, Best Inventory Management Software in Singapore.
