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Inventory Optimization Basics: Reducing Costs Without Stockouts

Learn the fundamental techniques for optimizing inventory levels, including EOQ, safety stock, and ABC analysis.

· 2 min read

Why inventory optimization matters

Inventory is usually one of the three largest line items on a distributor's balance sheet. Carry too much and you tie up cash, warehouse space, and risk obsolescence. Carry too little and you stock out, lose sales, and pay expedite fees to recover.

Optimization is the discipline of finding the smallest amount of inventory that still meets your service level target.

The three numbers every operator should know

1. Reorder point (ROP)

ROP = (Average daily demand x Lead time in days) + Safety stock

The reorder point tells you when to place a new purchase order. Hit this level and you reorder, no debate.

2. Safety stock

Safety stock = Z x sigma_LT

Where Z is the service-level factor (1.65 for 95%, 2.33 for 99%) and sigma_LT is the standard deviation of demand during lead time. Safety stock is the buffer that absorbs demand and lead time variability.

3. Economic order quantity (EOQ)

EOQ = sqrt( (2 x annual demand x order cost) / holding cost per unit per year )

EOQ tells you how much to order. It balances the fixed cost of placing an order against the cost of holding the resulting inventory.

ABC analysis: where to focus

Not every SKU deserves the same attention. Classic Pareto split:

  • A items (~20% of SKUs, ~80% of revenue): tight cycle counts, low safety stock, frequent review.
  • B items (~30% of SKUs, ~15% of revenue): standard policies, monthly review.
  • C items (~50% of SKUs, ~5% of revenue): higher safety stock is fine, quarterly review.

Run an ABC report quarterly. Items move between buckets as the business changes.

Inventory turnover and days on hand

Inventory turnover = COGS / Average inventory value
Days on hand = 365 / Inventory turnover

A jump in days on hand is the earliest warning sign of demand softening or over-ordering. Trend it monthly by category.

Five low-effort wins

  1. Kill dead stock. Anything with zero movement in 12 months is cash on the floor. Liquidate, donate, or scrap.
  2. Tighten lead time data. Most ROP calculations use the supplier's quoted lead time, not the actual measured one. Measure it.
  3. Differentiate service levels. Not every SKU needs 99%. Drop C-items to 90 to 95% and reclaim safety stock.
  4. Consolidate suppliers. Fewer POs, larger batches, lower order cost in the EOQ formula.
  5. Cycle count weekly. Annual physical inventory is too late to catch shrink and process errors.

Try the math

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