Most merchants track revenue and profit. Almost none track the inventory metrics that actually predict whether stockouts and overstock are coming. Here are the 9 numbers that matter.
You cannot manage what you do not measure.
Shopify gives you plenty of revenue and orders data. What it does not surface by default is the layer of inventory metrics that tells you whether your operations are healthy or quietly accumulating problems.
These are the nine numbers you need to review regularly — what they mean, how to calculate them, and what good looks like.
What it measures: How many times you sell and replace your full inventory in a given period.
Formula: Cost of Goods Sold / Average Inventory Value
Example: £240,000 COGS / £60,000 average inventory = 4× inventory turns
What it tells you: Higher is generally better — it means capital is cycling quickly rather than sitting idle. But very high turns can indicate you are running too lean and risking stockouts.
Benchmarks by category:
| Category | Good turns | Concerning |
|---|---|---|
| Fashion / Apparel | 4–6× | Below 3× |
| Health & Beauty | 6–10× | Below 4× |
| Electronics | 4–8× | Below 3× |
| Home & Garden | 3–5× | Below 2× |
| Food & Perishables | 12–20× | Below 8× |
How to improve it: Reduce dead stock, tighten safety stock levels, improve demand forecasting.
What it measures: How many days of sales your current stock can cover.
Formula: Current Stock / Average Daily Sales
Example: 420 units on hand / 15 units per day = 28 days of stock
What it tells you: The forward-looking view of stockout risk. A product at 5 days of stock with a 14-day lead time is already in trouble. A product at 180 days of stock is capital tied up in slow-moving inventory.
Target range: 30–60 days for most ecommerce categories. Seasonal products may intentionally run higher before peak season.
Days of stock is your most actionable daily metric. Run it for every SKU, sort descending, and your biggest inventory problems surface immediately at both ends — the near-zero SKUs at risk of stockout and the 200+ day SKUs costing you cash to hold.
What it measures: What percentage of your starting inventory you have sold in a given period.
Formula: Units Sold / (Starting Inventory + Units Received) × 100
Example: 180 units sold / (200 starting + 100 received) = 60% sell-through
What it tells you: How effectively demand converted your available inventory into revenue. Used heavily in fashion and seasonal categories to evaluate how a buying decision performed.
Benchmarks: - 80%+ sell-through: strong - 60–80%: acceptable, watch for end-of-season excess - Below 60%: overbought; likely to require markdowns
How to use it: Compare sell-through across products at the same stage of their season. Products significantly below the average need attention — either more promotion, a price reduction, or a flag to reduce next season's buy.
What it measures: What percentage of your SKUs are currently out of stock.
Formula: SKUs with zero inventory / Total SKUs × 100
Example: 23 out-of-stock SKUs / 340 total SKUs = 6.8% stockout rate
What it tells you: At the portfolio level, how often demand is hitting a wall. Industry benchmarks suggest a stockout rate above 5% is causing meaningful lost revenue.
A more useful variant: Lost sales value from stockouts — multiply the average daily sales rate of each stocked-out SKU by its price and the number of days it was unavailable.
What it measures: What percentage of your SKUs have a physical count that matches the Shopify record.
Formula: SKUs with zero variance / Total SKUs counted × 100
Example: 312 accurate SKUs / 340 total = 91.8% accuracy
What it tells you: How trustworthy your inventory data is. Every decision made with inventory data — reorders, safety stock levels, available-to-promise — degrades in quality as accuracy falls.
Benchmark: 95%+ is considered good. Below 90% indicates a systemic process issue.
How to improve it: Regular cycle counts, receiving audits, and anomaly detection to catch discrepancies before they compound.
What it measures: What percentage of your inventory value is lost to theft, damage, or administrative error.
Formula: (Recorded Value − Physical Count Value) / Recorded Value × 100
Example: (£82,000 recorded − £79,500 physical count) / £82,000 = 3.0% shrinkage
What it tells you: The direct cost of inventory loss. The UK retail average is approximately 1.3%; ecommerce tends to be lower (less physical theft) but damage and administrative errors compensate.
Benchmark: Below 1.5% is well-managed. Above 3% warrants a process audit.
What it measures: What percentage of customer orders you fulfilled completely from available stock without any backorders or substitutions.
Formula: Orders shipped complete / Total orders × 100
Example: 1,847 complete orders / 1,920 total orders = 96.2% fill rate
What it tells you: The customer-facing impact of your inventory management. A fill rate below 95% means roughly 1 in 20 customers is experiencing a fulfilment issue — a significant retention risk.
How to track it: You need order management data alongside inventory data. Flag any order that was shipped incomplete, required a substitution, or was cancelled due to stock unavailability.
What it measures: How much gross profit you generate for each pound of inventory investment.
Formula: Gross Margin / Average Inventory Cost × 100
Example: £120,000 gross margin / £60,000 average inventory = GMROI of 2.0
What it tells you: Whether your inventory is generating an acceptable return on the capital deployed. A GMROI below 1.0 means you are losing money on the inventory investment. Above 2.0 is healthy for most categories.
Why it matters: GMROI captures both margin and turns in a single number. A high-margin product that turns slowly may have a lower GMROI than a lower-margin product that turns quickly. It is the most complete single measure of inventory productivity.
What it measures: What percentage of SKUs were reordered before hitting their reorder point (proactively) versus after (reactively or in stockout).
Formula: Proactive reorders / Total reorders × 100
What it tells you: Whether your purchasing process is systematic or reactive. High reactive reorder rates indicate that reorder points are not set, not monitored, or not actioned in time.
Target: 85%+ of reorders should be triggered before stockout risk, not after.
You do not need to track all nine KPIs daily. A practical review cadence:
Daily: Days of stock per SKU, stockout rate Weekly: Fill rate, reorder cycle compliance Monthly: Inventory turnover, sell-through, accuracy rate Quarterly: GMROI, shrinkage rate
The daily metrics keep you out of immediate trouble. The monthly and quarterly metrics tell you whether your inventory strategy is working over time.
CoreCaptain's dashboard surfaces the most critical metrics automatically — days of stock, stockout risk, anomaly flags, and reorder alerts — so the information you need to act on is visible without having to run reports manually.
CoreCaptain detects phantom stock, sync errors, and inventory discrepancies automatically. 14-day free trial, no credit card required.
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