The Calculator Is Not the Feature
We publish a free economic order quantity calculator. It is indexed, it works, and it tells you how many units to order each time. If you then buy our product, there is nowhere to put that number — because our reordering does a subtraction, and a subtraction is not a policy.
On our site there is a calculator that will work out an economic order quantity for you. Feed it your annual demand, what it costs you to place an order and what it costs to hold a unit for a year, and it returns a number with the note: order roughly this many units each time.
It is a real calculator, it does the arithmetic correctly, and we built it partly because people search for one. That is worth admitting rather than dressing up.
Here is the part we would rather you heard from us than discovered in month three: our product cannot use the number it gives you.
What our reordering actually does
When stock falls to the reorder point, a rule can raise a purchase requisition automatically. That much is real and it works. The question is what quantity it asks for, and there are exactly two answers.
Either a fixed number you typed into the rule once, which never changes. Or, if you did not type one, the reorder point minus whatever stock you currently have — which is to say, just enough to get back to the line you were trying not to cross, and never one unit more.
Ordering exactly enough to return to your reorder point means arriving back at the threshold you set to warn you. The next order is already due on the day this one lands.
That second behaviour is the default, and it is the one worth understanding, because it is not a small approximation of a good policy. It is a different thing entirely: it replenishes to the warning line rather than to a sensible stock position, so it guarantees the maximum possible number of orders, each as small as possible — which is the precise opposite of what an economic order quantity is for.
What the calculator tells you, and what the product does with it
The calculator says The product does
Order this many each time Type a fixed number, or accept a subtraction
A fixed quantity can hold the calculator's answer, but it is frozen — it cannot move when demand, order cost or holding cost move, which is the whole reason the formula has three inputs.
Balances ordering cost against holding cost Considers neither
Nothing in the product records what an order costs you to place or what a unit costs to hold. The two quantities the formula trades off are not stored anywhere.
Assumes steady annual demand Reads no demand at all
The reorder quantity is computed from the reorder point and current stock. Consumption history exists in the system and is not consulted.
Produces a number to reorder on Raises a requisition against a department
And no supplier. Sourcing stays manual, so the automatic part ends before the part with money in it.
The honest summary of this table is that the calculator and the product were built by people solving different problems, and nobody joined them up. The calculator is on the marketing site. The reordering is in the application. They have never met.
Why this is a European post
Not because the arithmetic is different here. Because the expectation is.
A buyer evaluating stock software in the UK, Ireland or the Netherlands has usually met inventory planning as a discipline before they meet us — through a previous system, a consultant, a supply chain qualification, or simply because their sector has been optimising this for thirty years. The vocabulary is familiar and the questions are specific: what is the ordering policy, is it periodic or continuous, how is the order quantity determined, does it respect pack sizes and price breaks.
Those are exactly the right questions, and a vendor demonstrating an automatic reorder rule can answer them very badly by simply showing the rule firing. The rule does fire. It is what it asks for that matters, and nobody sees that in a demo.
In fairness to the subtraction
It would be dishonest to argue that everybody needs an economic order quantity. The formula rests on assumptions that are wrong more often than its popularity suggests: that demand is steady, that placing an order costs a fixed amount regardless of what is on it, that the unit price does not change with quantity, and that stock can be held without a shelf-life constraint.
Break any of those and the answer stops being economic. A business ordering perishables, or buying against price breaks, or consolidating many lines onto one supplier delivery, is right to ignore it. For plenty of operations, a simple top-up to a sensible level is a better policy than a formula whose assumptions their business violates.
The criticism is narrower and survives all of that: we offer one policy, it is the crudest available, and we publish a calculator implying otherwise.
If
you reorder a few dozen lines by judgement
The subtraction is fine and the automation is a convenience. Set a fixed quantity per rule where it matters and you have lost nothing.
If
your suppliers sell in cases, pallets or price breaks
Set a fixed quantity that matches the pack, and know that it will not adapt. The system will never round an order up to a full case on its own.
If
you plan properly and expect the system to hold the policy
We are not there. Ask us before you buy rather than after — and ask any vendor showing you an automatic reorder to tell you the quantity it asks for, not just that it fired.
What we would do about the calculator itself
One option is to take it down, and we considered it. We decided against it for a reason worth stating: the calculator is genuinely useful to somebody working out whether the formula suits them at all, and that is a real question that deserves a free tool.
What it should not do is imply that the product behind it will act on the answer. So it says so now, and this post exists partly to say it louder.
Four questions about any automatic reordering
When the rule fires, what quantity does it ask for and how was it derived?
What a straight answer sounds like
A formula or a field. Ours is a subtraction or a fixed number.
Why it matters
Every vendor can show you a rule firing. The quantity is the entire content of the feature and it is invisible in a demo.
Does the order quantity use consumption history?
What a straight answer sounds like
Yes with a demonstration, or no.
Why it matters
If demand is not an input, the policy cannot adapt to a business that grows or a season that arrives.
Will it round up to a full case or a price break?
What a straight answer sounds like
A demonstration on a real supplier's pack size.
Why it matters
Ordering seventeen of something sold in twenties produces a purchase order your supplier will change, which quietly breaks your matching later.
Does it choose a supplier?
What a straight answer sounds like
Usually no. Get it said plainly.
Why it matters
Automation that stops before sourcing saves the easy half of the work and leaves the half with money in it.
Three, in the order that would actually help
Notably, an economic order quantity engine is not first on this list, and we would push back on anyone who insisted it should be.
Pack sizes, minimums and multiples
Order in twenties because that is how it is sold. This is the least glamorous item here and the one that would improve the most purchase orders, because a quantity your supplier has to correct is a quantity that breaks receipt matching downstream.
An order-up-to level, distinct from the reorder point
Two numbers instead of one: the level that triggers, and the level you replenish to. This alone fixes the pathological behaviour of topping up to the warning line, and it is a far smaller build than a planning engine.
A calculated order quantity, with the inputs stored
Only worth doing once ordering cost and holding cost are recorded per item or per supplier, because without them any formula is guessing with extra steps. This is the one the calculator implies we already have, and it is genuinely third in usefulness.
If a planner tells you they need the third and cannot articulate the first two, they have been sold a formula rather than a policy. The first two are what make purchase orders arrive as agreed.
Tell us how you decide order quantitiesWhat AWRA OpsHub does today
- A reorder point per item, with an alert when stock crosses it.
- Automatic requisition raising, so crossing the line can create a purchase requisition without anybody watching a report.
- A fixed order quantity per rule, which can hold a number you calculated elsewhere.
- Requisition approval enforced before an order can be raised, so automation feeds a controlled process rather than bypassing it.
What it does not do
- No economic order quantity anywhere in the product. It exists as a public calculator on this website and nowhere else.
- No demand input to the order quantity. Consumption history is recorded and never consulted when sizing an order.
- No pack sizes, minimum order quantities or price breaks, so the system cannot round to a case or reach for a better price tier.
- No supplier selection. The requisition is raised against a department; who to buy from stays a human decision.
- No safety stock as a distinct concept from the reorder point, so lead-time risk and the reorder trigger are one number doing two jobs.
- No periodic review policy — reordering is triggered by crossing a level, never by a calendar.
Not ours, by choice
- We are not claiming an economic order quantity is the right policy for your business. Its assumptions are wrong for a great many operations, and a vendor selling it as universally correct is overselling a formula from the 1910s.
- We name no competitor and make no comparative claim about who does this better. What we can tell you precisely is what ours does, which is a subtraction.
The verdict
Publishing a calculator whose output your own product cannot accept is not a lie, but it is the kind of thing that erodes trust slowly if the buyer finds it themselves. So: the calculator is real and correct, the product reorders by subtracting stock from the reorder point, and those two facts have never been introduced to each other. If you reorder by judgement across a modest catalogue, none of this will cost you anything. If you expect the system to hold your ordering policy, ask the quantity question early — of us, and of everyone else. A demonstration of a rule firing answers a question nobody should be asking.
Bring us your ordering policy
Pack sizes, minimums, price breaks and how you decide what to order. We will tell you which parts we can hold today, which need a fixed number and a human, and whether the gap is small enough to live with.
Talk to us about reordering