What inventory turnover ratio means in FBA
Inventory turnover ratio tells you how many times per year you cycle through your entire stock. It is a financial efficiency metric: unlike sell-through rate (which uses units), turnover ratio uses dollar values, making it the right metric for comparing inventory efficiency across SKUs with different costs and price points.
For Amazon FBA sellers, turnover ratio connects your inventory decisions to your cash flow. A turnover of 6 means your capital is locked in inventory for about 60 days per cycle. A turnover of 3 means 120 days. Since FBA sellers typically finance inventory with working capital or loans, faster turnover directly reduces your cost of capital.
Turnover ratio is also the inverse of days sales of inventory (DSI). If you know one, you can calculate the other: DSI = 365 ÷ Turnover Ratio.
Inventory turnover ratio formula
Example: a $2.8M private label seller
A private label seller doing $2.8M in annual revenue with 25 SKUs (average selling price $45, average landed cost per unit $14).
- Annual COGS: ~62,222 units sold × $14 = $871,111
- Beginning inventory value (Jan 1): $126,000 (9,000 units × $14)
- Ending inventory value (Dec 31): $154,000 (11,000 units × $14)
- Average inventory value: ($126,000 + $154,000) ÷ 2 = $140,000
Inventory turnover ratio = $871,111 ÷ $140,000 = 6.2 turns/year
This means the seller replaces their entire inventory roughly every 59 days (365 ÷ 6.2). For a private label FBA business with 60 to 75 day lead times, 6.2 turns is solid.
| Turnover | Days per cycle | Assessment for FBA |
|---|---|---|
| > 12 | < 30 | Possibly understocked / frequent stockouts |
| 6 to 12 | 30 to 60 | Excellent for most FBA categories |
| 4 to 6 | 60 to 90 | Acceptable with long lead times |
| < 4 | > 90 | Slow; excess inventory likely |
FBA-specific considerations
Inventory turnover ratio in FBA requires adjustments that traditional retail does not:
FBA storage fees punish low turnover directly. Amazon charges monthly storage fees of roughly $0.87 per cubic foot (standard) and $2.40 (Q4). If your turnover drops below 4, the per-unit storage cost starts eating into your margins significantly. The financial penalty for slow turnover is built into the FBA fee structure in a way it is not in a self-managed warehouse.
COGS must include all landed costs. Many FBA sellers undercount COGS by using only the factory price. Your true COGS includes product cost, ocean freight, duties, tariffs, prep/labeling, and drayage. Undercounting COGS overstates your turnover ratio and gives you a falsely optimistic picture.
SKU-level turnover varies wildly. A catalog-wide turnover of 6 might hide a top SKU turning at 15 and three tail SKUs turning at 1.5. The slow SKUs drag down your IPI score and accumulate storage fees while the fast movers mask the problem. Always calculate turnover at the SKU level, not just the account level.
Common mistakes
- Using revenue instead of COGS. Revenue inflates the ratio because it includes your margin. A $45 ASP product with $14 COGS would show 19.6 turns using revenue vs. 6.2 turns using COGS. The COGS-based number is the correct one for inventory efficiency.
- Ignoring inventory in transit. If you have $50,000 in inventory on a container ship, that capital is committed but does not appear in your FBA on-hand inventory. For a true picture of cash tied up in inventory, include in-transit inventory in your average inventory value.
- Chasing high turnover without considering stockout risk. A turnover above 12 (under 30 days per cycle) with a 60-day lead time means you are constantly at risk of stockouts. The goal is to match turnover to your lead time plus a safety buffer, not to maximize the number blindly.