Days onHand.Explained for people who hate math

Picture order day. You open the inventory report and two lines jump out. Demo Day Reserve, the premium eighth: 60 units on hand. Always Gone Gardens, the value quarter: 12 units on hand. Your gut does the math your gut always does. Sixty is a lot. Twelve is a little. Reorder Always Gone Gardens, relax about Demo Day Reserve, go get a coffee.

Now add one more column. Always Gone Gardens sells about 30 units a week. Demo Day Reserve sells about 2.

That changes the story completely. Always Gone Gardens has roughly three days left before the shelf goes bare on your busiest rung. Demo Day Reserve has thirty weeks. Thirty. That eighth will still be sitting there at Christmas, and it has a decent shot at being there next spring, quietly losing terpenes and gaining a reputation.

“Units on hand” is a number with no context. It’s like asking how far away a city is and being told “400.” Miles? Minutes? Dollars? Units on hand only becomes useful when you put it next to how fast the thing actually moves. That’s all weeks of supply is: inventory, measured in time instead of units.

In the ladder piece, I said a ladder shows coverage, not performance. This is the performance half. The ladder tells you where things sit on the shelf. Weeks of supply tells you how long they’re going to sit there.

If it helps, think of it as the “miles to empty” number on a car dashboard. The gas in the tank is your units on hand. How hard you’re driving is your sales rate. Miles to empty combines the two into the only thing you actually care about: how long until you’re stuck on the side of the road.

Let’s go back to the small flower category from the ladder piece. Same fictional brands as the ladder diagram, now with names that match their personalities (each still starts with its old letter), plus The Big Bag, the value ounce that filled the gap. The numbers below are made up for illustration, but the patterns are ones every buyer will recognize.

A few things jump out once the numbers are in time instead of units.

Boring But Beautiful and Copycat Cultivars both have 40 units. On a units report they look like twins. In weeks they’re not even in the same zip code: Boring But Beautiful turns over in a month, while Copycat Cultivars, which has the personality of a photocopy, sits for a season. This is the “two near-identical SKUs” circle from the ladder exercise, now with a price tag attached. If they’re splitting the same shopper, the copy is losing, and your money is sitting in its box.

Fancy Pants Reserve has the smallest pile on the shelf and still has twelve weeks of supply. Small numbers can hide long tails. A top-shelf SKU that sells one unit every two weeks doesn’t need a reorder; it needs a conversation about whether that rung is working or just present.

And Always Gone Gardens, the one with 18 units that looks fine at a glance, is the actual emergency. The name was a warning. Fast movers on the value rung are where empty shelves happen first, and an empty value rung is the exact gap the ladder piece was about. You fill a missing rung, then forget to watch it, and you’ve rebuilt the hole with extra steps.

The formula is simple. The bottom half of it, “average units sold per week,” is where the trouble lives. Here are the usual suspects.

Here’s where weeks of supply stops being a report and starts doing work. Instead of asking “how many should I order?”, ask “how many weeks do I want on the shelf after this order lands?” That target has three ingredients: lead time (how many weeks from placing the order to having it sellable), order cycle (how many weeks until you’ll place your next order for this vendor) and a cushion (a little extra for the busy weekend you didn’t see coming).

Say your vendor delivers in about a week, you order from them every two weeks, and you like one week of cushion. That’s a target of four weeks.

Now the order basically writes itself:

Always Gone Gardens sells 24 a week. Four weeks of that is 96 units. You have 18 on hand and nothing on order, so you order 78. Copycat Cultivars sells 3 a week. Four weeks is 12 units, and you have 40. You order zero, and you now know you’re carrying about 28 units of money that would rather be somewhere else.

The target won’t be the same on every rung. Fast value SKUs punish you hard for running out, so a little extra cushion there is cheap insurance. Slow top-shelf SKUs punish you slowly, by tying up cash and aging on the shelf, so a leaner target usually makes more sense. The point isn’t to find the one perfect number. It’s to decide your number on purpose instead of letting the last rep who visited decide it for you.

The ladder and weeks of supply are better as a pair. The ladder asks whether something is in each spot. Weeks of supply asks whether that something is moving. An empty rung is a question. A full rung with fifteen weeks of supply is a question too, just a more expensive one.

None of this takes a math degree. It takes one division problem and the habit of doing it before you trust your gut about a pile of boxes. Sixty units can be nothing to worry about. Twelve units can be an emergency. The number that tells you which is the one measured in weeks.