Putaway & Storage

Where inventory lives determines how efficiently every picker in the building works. Putaway strategy is a long-lived decision — poor choices compound into ghost inventory, failed cycle counts, and irreversible cube waste.

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Directed vs. Undirected Putaway

Undirected putaway: Worker decides where to put product based on personal memory. Works briefly in tiny operations. Destroys accuracy and cube utilization over time. Common symptom: same SKU in 6 locations across 3 zones, none of which are the designated slot.

Directed putaway: WMS assigns every location. The sequence:

1. SKU Profile Lookup — velocity class, dimensions, weight, temperature, hazmat, lot/expiration
2. Slot Availability Check — real-time: open, correctly sized, not at capacity, storage-compliant
3. Business Rule Application:
   • ABC zone assignment (A-items near outbound, C-items in far aisles)
   • FIFO/FEFO for dated product (food, pharma)
   • Family grouping (co-picked SKUs stored adjacent)
   • Hazmat segregation
4. Task Assignment — operator receives: “Put pallet 001234 in location A-01-03-02.” RF scan or voice confirmation. Instant WMS update.

Result: receiving accuracy above 99.9% because every put is confirmed, not assumed.

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Task Interleaving: Free Productivity

The problem: Without interleaving, a forklift completes putaway and drives back to staging empty. Deadhead travel — moving but producing nothing.

The fix: WMS routes operator directly from putaway completion to the nearest open pick or replenishment task before returning to staging.

Result: 15-25% lift truck productivity gain. On a 50-truck fleet, that’s 7-12 trucks of additional productive capacity — no new equipment, no new hires. It’s a WMS configuration decision.

Task interleaving is free productivity. The truck moves either way — the WMS decides whether it moves productively or empty.

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Four Storage Strategies

Strategy	Selectivity	Space Efficiency	WMS Dependency	Best For
Fixed Location	100%	Low (reserved slots sit empty)	None	<3,000 SKUs, manual systems, stable assortments
Random (Dynamic)	100%	Maximum	Complete	High-SKU 3PLs, constantly changing product mix
Class-Based (ABC)	100% within zone	High	Moderate	Most modern DCs — best balance
Combination	Variable	Variable	Moderate-high	Mixed operations with distinct channels

Class-Based storage is the standard in modern DCs:

• A-items in Zone 1 (near outbound/packing), B-items in Zone 2, C-items in far aisles
• Within each zone: random location assignment for cube efficiency
• Gets travel efficiency of fixed-zone + cube efficiency of random

Random storage warning: Complete WMS dependency. If WMS goes down, picking and putaway stop. Plan for system redundancy.

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The 85% Cube Rule

Warehouse cube utilization should not exceed 85% of theoretical capacity under normal operating conditions. Above 85%:

• Pick face replenishment becomes congested
• Overflow inventory blocks travel paths
• Put-away errors spike (no good location available, operators improvise)
• Cycle count accuracy degrades

The 15% buffer absorbs seasonal peak inventory without operational breakdown. When designing storage capacity, always size to peak inventory (not average) and maintain the 85% ceiling at that peak.

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Slotting Optimization

Moving fast-moving SKUs closer to outbound/packing is the highest-ROI non-capital improvement in most DCs.

ABC classification inputs:

• Basic velocity: units sold / days (default for most operations)
• Weighted velocity: (units sold × order frequency) / days (for sporadic demand)
• Volume-based velocity: (units sold × unit volume) / days (space-constrained ops)

Standard ABC split:

• A items: ~20% of SKUs, ~80% of picks → prime pick locations, golden zone
• B items: ~30% of SKUs, ~15% of picks → secondary locations
• C items: ~50% of SKUs, ~5% of picks → high-density storage, less-accessible locations

Re-slot frequency: Monthly at minimum for fast-changing SKU velocity profiles (e-commerce, fashion). Quarterly for stable operations.