Inventory turnover formula
Inventory turnover — often called "inventory turns" — is the number of times per year you sell through your average inventory. The formula is Turns = COGS / Average Inventory. If you did $500,000 in cost of goods sold last year and your average inventory balance was $100,000, you turned inventory five times — every 73 days on average.
Turns is the single most important operational metric for retail, ecommerce, and distribution businesses. Faster turns mean less capital tied up, fresher product, less markdown risk, and better cash flow. Slower turns mean dead stock, storage cost, and products that may not sell at full price. Most failing retailers have inventory problems before they have revenue problems.
Days of inventory — the other way to see it
Days of inventory is 365 / Turns. A five-turn business holds about 73 days of inventory. A fifteen-turn grocery store holds about 24 days. The more perishable or seasonal the product, the fewer days you want to hold. Fashion runs 4–6 turns because trends shift quickly; electronics runs 6–10 turns because new models replace old; groceries run 14–20 because food spoils.
Industry benchmarks
- Grocery / supermarket: 14–20 turns.
- Apparel / fashion: 4–6 turns.
- Electronics: 6–10 turns.
- Furniture: 2–4 turns.
- Auto parts retail: 4–6 turns.
- Hardware stores: 3–5 turns.
- Jewelry: 1–2 turns.
- Ecommerce DTC (consumables): 8–12 turns.
- Ecommerce DTC (durable goods): 4–8 turns.
- Office supplies / MRO: 6–8 turns.
Compare your turns number to your industry. Running well below the range means cash is tied up in stock and carrying cost is eating margin; running well above could mean you're stocking out and losing sales to competitors who have product in stock.
Reorder points and safety stock
The reorder point is the inventory level at which you place a new order from your supplier. The formula is Average Daily Usage × Lead Time + Safety Stock. If you sell 10 units per day of a product and your supplier takes 14 days to deliver, you need to reorder when you have 140 units left plus some safety margin. The calculator above shows the core reorder level; add 20–30% safety stock to cover demand spikes and supply delays.
For A-class SKUs (top 20% of revenue), err high on safety stock — the cost of a stockout is higher than the carrying cost. For C-class SKUs (bottom 50%), err low — most C-class items don't justify tight safety stock and you're better off with an occasional stockout. See our EOQ calculator for optimal order quantity given holding and ordering costs.
Why slow turns are expensive
Slow-moving inventory is expensive three ways. First, it ties up cash that could be earning a return elsewhere — typically 15–25% opportunity cost at a small business's WACC. Second, it costs storage: warehouse rent, shrinkage, handling, and insurance typically add 20–30% per year to the cost of inventory held beyond a reasonable turn rate. Third, slow items are discount risk — the longer it sits, the higher the chance you mark it down to move it, and the markdown usually exceeds the carrying cost you've already paid.
If you have inventory that hasn't turned in 12 months, it's almost certainly worth discounting 30–50% to convert to cash. Accountants call this "carrying cost" and most small businesses underestimate it by at least half. Our cash flow calculator helps you see the impact on bank balance when you convert slow stock to cash.
Inventory velocity vs profitability tradeoff
Higher turnover doesn't always mean higher profit. You can increase turns by stocking less, but that risks stockouts and lost sales. You can increase turns by cutting prices, but that hurts margin. The right target is "highest turns at full margin" — push turns up without discounting, through better forecasting and more disciplined SKU management. Turns bought by markdowns is a false win.
SKU-level analysis beats aggregate
Whole-business inventory turns can mask huge variation at SKU level. Most businesses follow a Pareto rule: 20% of SKUs drive 80% of turns. The other 80% of SKUs often turn 1–2 times/year and eat carrying cost disproportionately. Run turns by SKU at least quarterly and consider dropping or consolidating the bottom quartile. Most retail businesses carry 30–50% more SKUs than they should.
Seasonality and turns
Seasonal businesses need seasonal reorder points. A pool-supply store reorders chlorine heavily in March–May and minimally in November. If you apply a flat reorder point year-round, you'll either stock out in peak or carry dead stock in off-season. Simplest handling: recalculate reorder points once per quarter using the trailing 90-day usage rate, not the annual average. Pre-season buy reviews 60 days before peak prevent the classic "ordered too little / ordered too much" swing.
Just-in-time vs safety stock
Just-in-time inventory — holding minimal stock and relying on fast supplier turnaround — minimizes capital tied up but creates risk when supply chains hiccup. Post-2020 most businesses have moved back toward holding more safety stock. Reasonable middle ground: hold enough safety stock to cover 120–150% of lead time for A-class SKUs, tighter for B/C-class. Multi-source critical SKUs where possible — single-supplier dependency has become a meaningful operational risk.
Tools that make this easier
Shopify, Square, Lightspeed, and most inventory-management platforms track turns natively. If you're running on spreadsheets, pull COGS from your P&L and calculate average inventory as the average of beginning and ending balance for the period. Pair this calculator with the working capital calculator to understand the cash-tie-up angle lenders care about, and with the EOQ calculator for order-size optimization.