Inventory KPIs: the 8 metrics actually worth tracking
Most inventory dashboards surface thirty numbers; you need three of them on a given Tuesday. These are the eight inventory KPIs that explain whether your stock is working — turnover, days on hand, shrinkage, sell-through, GMROI, carrying cost, stockout rate, and fill rate — each with its formula and what a healthy number looks like.
What is an inventory KPI?
An inventory KPI is a key performance indicator — a single measured number that tells you how well your inventory is doing one specific job, like turning cash over, staying in stock, or staying accurate. The distinction from a plain metric is intent: you can measure a hundred things about your stock, but a KPI is a number you have decided to watch because it changes a decision. A KPI you review but never act on is trivia, not management.
Inventory KPIs fall into three broad jobs: cash efficiency (is money moving or trapped on a shelf?), service level (are you in stock when a customer wants to buy?), and accuracy (can you trust the records the first two depend on?). The eight KPIs below are grouped by those three jobs. Track all eight, but as the closing sections explain, only three of them earn a monthly review — the rest move slowly enough for a quarterly look.
Cash-efficiency inventory KPIs
1. Inventory turnover. Turnover measures how many times you sell through your average inventory in a period — the headline read on whether cash is moving or sitting. Formula: inventory turnover = COGS ÷ average inventory. Good looks like a figure that beats your own trailing 12 months; a rising trend matters more than any generic industry number (grocery runs 12–25 turns a year, general retail 4–8, furniture 2–4).
2. Days inventory outstanding (DIO). DIO restates turnover in days instead of times per year — how long, on average, a dollar of stock sits before it sells. Formula: DIO = 365 ÷ inventory turnover. Good looks like falling DIO on stable sales; a sudden jump usually means overbuying or slow movers before it shows up as a cash problem.
3. GMROI (gross margin return on inventory investment). GMROI answers what turnover alone cannot: for every dollar tied up in stock, how many dollars of gross margin does it earn back? Formula: GMROI = gross margin dollars ÷ average inventory cost. Good looks like above 1.0 at minimum — the stock earns back more than it costs to hold — with most healthy retail categories running 2–3.
4. Carrying cost. Carrying cost is the annual cost of simply owning inventory — capital tied up, storage, insurance, and obsolescence risk — as a share of inventory value. Formula: carrying cost rate = annual holding cost ÷ average inventory value. The typical range is 15–30% per year; good looks like the low end and stable, since a rising rate usually signals aging stock, not a bigger storage bill.
Service-level inventory KPIs
5. Stockout rate. Stockout rate is the share of time a SKU sat unavailable to sell — every day at zero is a sale you cannot recover. Formula: stockout rate = stockout days ÷ total days, per SKU. Good looks like under 2–5% for your high-value A items; low-value C items can tolerate more.
6. Sell-through rate. Sell-through tells you what share of what you bought actually sold in a window — the fastest signal that you over- or under-bought something. Formula: sell-through rate = units sold ÷ units received × 100. Good looks like 80% or more within your normal reorder window for regularly stocked items; well below that and cash is tied up in slow movers.
7. Fill rate. Fill rate measures how often you ship a customer’s order complete on the first attempt — no backorders, no partial shipments. Formula: fill rate = orders shipped complete ÷ total orders × 100. Good looks like 95% or higher; below 90% and stockouts are costing you repeat customers, not just single sales.
Accuracy inventory KPIs
8. Shrinkage rate. Shrinkage is the gap between what your records say you hold and what a physical count finds — theft, damage, admin error, and supplier shortfalls in one number. Formula: shrinkage rate = (recorded − physical) ÷ recorded × 100. Good looks like under roughly 2% and trending down, not up.
Accuracy earns its own category because it sits underneath the other seven. Turnover, GMROI, and fill rate are all computed from your recorded quantities; if shrinkage is high, those records are wrong, and every KPI built on them is wrong too. That is why shrinkage rate makes the short list of KPIs to review monthly — not because stock walking out the door is common, but because an untrustworthy record quietly poisons the whole dashboard.
Which three inventory KPIs to start with
If you only review three of the eight, make them the three that map to the three jobs. Inventory turnover is your read on cash — the fastest signal that money is trapped in unsold stock rather than moving. Stockout rate is your read on sales — it tells you directly what demand you are failing to capture, in close to real time. Shrinkage rate is your read on accuracy — without it, every other number on the list is built on records you cannot fully trust.
Review those three monthly. The remaining five — DIO, sell-through, GMROI, carrying cost, and fill rate — are genuinely useful diagnostics, but they move slowly enough that a quarterly review catches problems in time. This is the whole discipline: track all eight so the picture is complete, but act on the three that move first, so a review turns into a decision instead of a dashboard you scroll past.
How StockZip surfaces these inventory KPIs
Most of these KPIs already live in data you are generating. Every add, remove, move, and adjustment is written to StockZip’s movement history with a timestamp and an actor, so turnover, shrinkage, and sell-through fall out of that audit trail rather than a spreadsheet you maintain by hand. Per-item minimum levels and low-stock alerts — both available on the Free plan — keep stockout rate down by warning you before a SKU hits zero.
The honest caveat is the reporting layer. StockZip’s inventory valuation, profit-margin, and activity reports — the tools that compute turnover, GMROI, and carrying cost into finished numbers — are a paid feature, available from the Starter plan up. The Free plan does not include reports, so on Free you would still be exporting movement data to calculate these KPIs yourself. What Free gives you is the clean, timestamped movement history the calculations depend on; a paid plan turns that history into the finished KPI without the spreadsheet step.