Key Takeaways
- Inventory accuracy is measured at the unit level, not the SKU level — 99.9% unit accuracy is the practical industry benchmark.
- 99.9% unit accuracy still means ~1 missing or miscounted unit per 1,000 — over a year, that's real money for high-value SKUs.
- Cycle counting (rolling daily counts of a subset of bins) catches drift before a full annual count does.
- A good 3PL writes inventory accuracy into the SLA and reimburses for shrinkage above an agreed threshold.
How is inventory accuracy measured?
There are two common definitions, and the difference matters:
- Location accuracy — Does the WMS-reported quantity in each bin match the physical count? Industry benchmark: >99%.
- Unit accuracy — Of all units in the building, what % are in the right place with the right count? Industry benchmark: >99.9%.
What does cycle counting look like in practice?
Instead of shutting down for an annual physical inventory, a mature 3PL counts a slice of the warehouse every day on a rolling cycle. Typical cadence: A-velocity SKUs (top movers) counted monthly, B-velocity counted quarterly, C-velocity counted annually.
Discrepancies trigger a root-cause investigation: was it a put-away error, a pick error, damage write-off, or theft? A 3PL that just adjusts the number without finding the cause has a deeper accuracy problem.
What should you demand in the contract?
- A written inventory accuracy SLA at the unit level (99.9% or better).
- A weekly or monthly inventory variance report shared with you automatically.
- A shrinkage reimbursement clause above an agreed threshold (e.g., the 3PL covers shrinkage above 0.1% of units received).
- An end-of-year inventory reconciliation, with the 3PL covering the cost of the count.
What can you do to keep inventory accurate on your side?
- Send accurate ASNs (advance ship notices) for every inbound, with case-pack quantities and lot/batch info.
- Use unique, machine-readable barcodes on every unit — not the manufacturer's UPC if it scans inconsistently.
- Reconcile your Shopify on-hand to the 3PL's WMS weekly, not monthly.
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