Order Size Calculator
How much to order at a time is the half of the inventory problem that hides in plain sight. Order sizes are usually a habit, and the habit ages while the business changes around it. This runs the standard answer from three numbers you mostly already know.
Everything happens in your browser, and nothing you type is sent anywhere or saved. The other half of the problem, when to place the order, is the reorder point calculator.
Order this many
427 units
42.7 orders a year, about every 9 days
The two costs at that quantity
$2,133 + $2,133
Ordering + carrying, $4,266 a year in all
Why these two numbers always come out equal
Annual demand: 18,200 units.
How it decides
Each order costs you something fixed, and everything you hold costs you something ongoing. One falls as orders get bigger, the other climbs, and this finds the quantity where their sum bottoms out.
What it will not tell you
It assumes your price per unit stays the same at any order size. A real volume discount changes the math, sometimes decisively — run the total both ways rather than assuming. Perishables cap the order size before the arithmetic does. And a seasonal business should run its busy and slow stretches separately, because an average of two different businesses describes neither.
The part the math misses
Most order sizes start as a guess that survived. A shortage teaches a bigger number, a crowded storeroom teaches a smaller one, and after a few years the habit feels like knowledge. The math above prices that habit one item at a time. What it cannot weigh is your afternoon. Repricing a whole storeroom, item by item, is the kind of work that pays and never gets scheduled.
If that sounds like your operation, that is the kind of thing worth a conversation.