7 Inventory KPIs Every Ecommerce Brand Should Track (2026)
Most brands track revenue and gross margin and call it a day. These seven inventory KPIs are the ones that actually tell you whether your stock is working for you or quietly bleeding cash — with the formula and a healthy range for each.
Quick Answer
The seven inventory KPIs that matter most for ecommerce brands in 2026 are: (1) inventory turnover, (2) days of supply, (3) sell-through rate, (4) in-stock / stockout rate, (5) GMROI, (6) aged / excess inventory %, and (7) forecast accuracy. Together they answer the four questions that decide profitability: Is cash moving (turnover, days of supply)? Are products selling at the planned pace (sell-through)? Are we losing sales to stockouts (in-stock rate)? And is our inventory actually earning (GMROI)? Track them per SKU and per channel, not just company-wide.
The 7 KPIs, with formulas + healthy ranges
Inventory turnover
Is cash moving?How many times you sell through and replace average inventory in a year. Formula: COGS ÷ average inventory (at cost). Healthy: ~4–8x for most ecommerce; higher for consumables, lower for high-AOV durables. Too low = overstock; too high = stockout risk. Full turnover guide here.
Days of supply (Days Inventory Outstanding)
How long will stock last?The turnover ratio expressed as days — far more actionable for planning. Formula: 365 ÷ inventory turnover (or current stock ÷ daily sales rate). Healthy: depends on lead time + safety stock, but it should comfortably exceed your replenishment lead time. This is the number that tells you when to reorder.
Sell-through rate
Selling at the planned pace?The percent of available inventory sold in a period. Formula: units sold ÷ (units sold + units on hand) × 100, over the period. Healthy: commonly 40–80% monthly depending on category and replenishment cadence. Low sell-through flags slow movers heading toward dead stock; very high flags under-buying.
In-stock rate (and its mirror, stockout rate)
Losing sales to stockouts?The percent of time (or SKUs) you're in stock and sellable. Formula: in-stock SKU-days ÷ total SKU-days × 100. Healthy: 95–98%+ on your A-items. On Amazon, stockouts cost double — lost sales and rank/Buy-Box damage that lingers after you restock. Stockout-prevention playbook.
GMROI (Gross Margin Return on Inventory Investment)
Is inventory actually earning?How many gross-margin dollars you earn per dollar invested in inventory — the KPI that ties inventory to profit. Formula: gross margin ÷ average inventory cost. Healthy: above 1.0 means you're earning more than the inventory costs to hold; many healthy brands target 2.0–4.0+. Reveals SKUs that turn well but barely make money.
Aged / excess inventory %
How much is dead weight?The share of inventory value sitting beyond a target age (e.g., 90/180/365 days). Formula: value of aged stock ÷ total inventory value × 100. Healthy: as low as possible — on Amazon, 181+ day stock triggers the aged-inventory surcharge, so this KPI maps directly to a fee. Watch it climb before Q4. Aged-surcharge math.
Forecast accuracy
Can you trust the plan?How close your demand forecast lands to actual sales. Formula: 100% − MAPE (mean absolute percentage error), tracked per SKU. Healthy: varies by demand volatility, but rising accuracy over time is the signal that matters. This is the meta-KPI: improve it and turnover, in-stock rate, and aged % all improve together. The forecasting process.
The 7 at a glance
| KPI | Formula | Healthy range |
|---|---|---|
| Inventory turnover | COGS ÷ avg inventory | ~4–8x (category-dependent) |
| Days of supply | 365 ÷ turnover | > replenishment lead time |
| Sell-through rate | sold ÷ (sold + on hand) | ~40–80% monthly |
| In-stock rate | in-stock days ÷ total days | 95–98%+ on A-items |
| GMROI | gross margin ÷ avg inv cost | >1.0; target 2.0–4.0+ |
| Aged / excess % | aged value ÷ total value | As low as possible |
| Forecast accuracy | 100% − MAPE | Rising over time |
Ranges are directional — benchmark against your own category, margin, and lead times.
The honest caveat
Don't track all seven from day one — you'll drown in dashboards and act on none of them. Start with two: days of supply (so you reorder on time) and in-stock rate (so you catch lost sales). Add GMROI and aged % once those are habit. And remember the trap: a company-wide average can look perfectly healthy while masking a hero SKU stocking out and a dog SKU rotting — the value is entirely in the per-SKU, per-channel cut.
Frequently asked questions
What are the most important inventory KPIs for ecommerce?
The seven that matter most: inventory turnover, days of supply, sell-through rate, in-stock/stockout rate, GMROI, aged/excess inventory %, and forecast accuracy. Together they tell you whether cash is moving, products are selling at the planned pace, you're losing sales to stockouts, and your inventory is actually earning. Track them per SKU and per channel, not just company-wide.
What is a good inventory turnover ratio?
Roughly 4–8x a year for most ecommerce brands — higher for fast-moving consumables, lower for high-AOV durables. Below ~4x usually signals overstock; above ~10–12x can mean you're too lean and risking stockouts. It's category- and margin-dependent, so benchmark against your own. Full turnover guide.
What is GMROI and why does it matter?
GMROI (Gross Margin Return on Inventory Investment) = gross margin ÷ average inventory cost. It measures how many margin dollars you earn per dollar tied up in stock. Above 1.0 means inventory earns more than it costs to hold; many healthy brands target 2.0–4.0+. It's the KPI that catches SKUs that turn quickly but barely make money — high turnover hides low GMROI.
How do you measure forecast accuracy?
The common method is 100% minus MAPE (mean absolute percentage error) — the average absolute gap between forecast and actual sales, tracked per SKU. The absolute number depends on how volatile your demand is; what matters is the trend. Rising forecast accuracy is the meta-KPI: improve it and turnover, in-stock rate, and aged-inventory % all improve together.
Which inventory KPIs should I start with?
Start with two: days of supply (so you reorder before stockouts) and in-stock rate (so you catch lost sales). Those two prevent the most expensive mistakes. Add GMROI and aged/excess % once the first two are a habit, then layer in the rest. Tracking all seven from day one usually means acting on none of them.
Why track inventory KPIs per channel instead of company-wide?
Because a company-wide average hides the truth. The same SKU can be perfectly healthy on Shopify and stocking out on Amazon — the blended number looks fine while you lose sales on one channel and sit on dead stock in another. Inventory KPIs only become a decision system when measured per SKU per channel.