Days of Inventory on Hand

Days of inventory on hand is the most physical way to talk about working capital trapped in stock. The number maps to bins and shelves and trucks. Forty-five days on hand means a month and a half of bins sitting in the stockroom. Fifteen days is two and a bit weeks. The intuition is much easier than the turns version, which is why operations conversations usually default to days while finance defaults to turns. Both numbers point at the same problem.

"Every day of inventory on hand is a day of cash sitting still."

How days of inventory on hand works

The calculation takes the average value of inventory you carry, in dollars at cost, and divides by daily cost of goods sold. A shop with $750,000 of average inventory and $5 million of annual COGS is burning about $13,700 a day, which works out to roughly 55 days on hand. The arithmetic is easy; the discipline lives in what you include.

What to include in the count

• Raw material. Bar stock, resin, components, packaging waiting to be consumed.
• Work-in-process. Material that has started its journey but is not yet finished.
• Finished goods. Completed product waiting to ship.
• Average, not snapshot. Inventory bounces with shipments and receipts. A single point-in-time count can mislead by 20 percent or more.

The decomposition by category is where the diagnostic value lives. A shop with 60 days overall might be 20 days of raw, 10 days of WIP, and 30 days of finished goods. The finished goods bucket tells a different story than the raw bucket: too much raw means the buyer is over-ordering; too much finished means the shop is producing ahead of demand. The shop-wide number cannot tell you which conversation to have.

Where days of inventory on hand fits on the shop floor

Imagine a 25-person packaging shop running corrugated cases for two beverage customers. The shop carries about $400,000 in inventory: $200,000 in liner and corrugating medium, $80,000 in glue and ink, $90,000 in WIP, $30,000 in finished cases waiting to ship. Annual COGS is $2.8 million, so daily burn is about $7,700. Overall days on hand is 52.

The owner is comfortable with 52 days because the supplier lead time for liner is two weeks and there is no obvious problem. The breakdown tells a more useful story. The liner alone is 25 days, which is more than safety needs require, because a previous shortage left the buyer cautious. The glue category is 35 days because a discontinued color is sitting on the shelf. The finished goods bucket is fine. The actionable conversations are with the buyer about liner sizing and with the customer about the dead glue.

The shop moves liner from 25 to 15 days through a weekly delivery agreement with the supplier instead of monthly. The dead glue is sold back to the supplier at a discount. Overall days on hand drops from 52 to 38. The shop has freed about $100,000 of working capital without changing anything about how it produces. The metric did its job: it surfaced the cash trapped on shelves so it could be released.

Common mistakes with days of inventory on hand

• Reading the shop-wide number in isolation. The diagnostic value is in the category and SKU breakdown. The total alone hides where the cash actually sits.
• Treating low days on hand as inherently better. A shop running 12 days is great until it stocks out and loses a customer. Service has to keep pace with the trim.
• Ignoring the trend. A snapshot can be misleading. The same metric over four quarters tells you whether the operating system is improving or sliding.
• Comparing across industries. A precision parts shop and a food processor cannot use each other's days-on-hand benchmarks. Compare against your own history.
• Conflating days on hand with availability. Higher days does not mean safer supply if the wrong items are sitting on the shelf. A pull system with smaller, faster cycles can run with fewer days and better availability at the same time.

Days of inventory on hand and related Lean tools

Days of inventory on hand is the duration-side companion of inventory turns. They are reciprocals of each other once the time base is matched. Most days on hand growth points at excess inventory, the lean waste that hides in slow-moving SKUs. Properly sized safety stock is the deliberate part of days on hand; the rest is usually opportunity. DOH belongs on the lean KPI dashboard alongside throughput and on-time delivery.