Reorder Quantity: How Much Stock to Order

You hit your reorder point. The purchase order screen is open, the supplier is selected, and there's one blank field left: quantity. The reorder point told you when to order. It has nothing to say about how much.

What reorder quantity answers

Reorder quantity is the number that goes in that field: how many units you buy this time, now that your reorder point has told you it's time to buy at all. It's a separate calculation from the reorder point, worked out from a different question: not "is it time?" but "how much gets me through until the next order without leaving cash sitting on a shelf?"

The reorder point formula already covers when to trigger an order, with a worked example on "Cedar & Fig, 250g." This post picks up from there. For a shorter side-by-side of the two concepts, see reorder point vs. reorder quantity.

The formula

Reorder quantity = Target stock level − (Stock on hand + Stock on order)

Three ingredients:

• Target stock level: the total you need on hand or on order to reach your next planned purchase, covered in full in how much inventory you should keep. This post treats that number as an input, not something to recalculate here.
• Stock on hand: what's physically on the shelf right now, which at the moment you cross the reorder point is roughly the reorder point itself.
• Stock on order: units already on a purchase order that hasn't arrived yet. If nothing is currently on order, this is zero.

Order enough to close the gap between what you have and what you'll need. Not more: that's cash tied up in shelf space. Not less: that's a smaller second order later, usually at a worse shipping rate.

A worked example

Back to Cedar & Fig, 250g. Its reorder point is 90 units, and its target stock level is 240 units, the same sales velocity and lead time extended out to the 30 days until the next planned order. Stock just dropped to 90, and nothing else is on order.

Reorder quantity = 240 − (90 + 0) = 150 units. That's the number the formula wants — the next section covers what actually gets typed into the purchase order.

MOQs and case packs

150 is rarely the number you actually order, because suppliers sell in fixed units of their own: a minimum order quantity (MOQ), a case pack, or both.

Say this candle ships in cases of 20. 150 ÷ 20 = 7.5, and a supplier won't cut a case in half: round up to 8 cases, or 160 units, and you're carrying 10 extra units decided by the case pack rather than a guess. If the supplier's MOQ were 200 units regardless of case size, you'd order 200, not 150, and the surplus becomes safety stock for a future cycle rather than waste.

Doing this by hand means knowing every supplier's rounding rule and reapplying it to a different number every reorder cycle, across however many SKUs you carry. That's the part that gets skipped as a catalog grows — StockCue's buying planner applies each supplier's MOQ and case-pack size automatically once you've entered their terms, on Starter and up.

Why not the EOQ formula?

If you've read a supply-chain textbook, you may expect a different formula here: Economic Order Quantity, Q* = √(2aK / h), where a is a constant demand rate, K is the fixed cost of placing an order, and h is the cost of holding one unit for one period.

EOQ is a real, well-established formula, and the operations-research textbook it comes from is explicit about what it assumes: a known constant demand rate, an order that arrives all at once after a fixed lead time, and no planned shortages. The same source says those assumptions "seldom are satisfied completely in practice," and a seasonal or promo-driven SKU is exactly the case where constant demand doesn't hold. It also notes EOQ tends to stay roughly accurate even when its assumptions are only approximate, but its own guidance is to sanity-check the model first when the assumptions are badly off, not apply it blind.

There's a more practical reason it doesn't show up above: EOQ needs an ordering cost and a holding cost per unit, and almost no small merchant tracks either one with any precision. The target-stock-level formula uses numbers you already have (sales velocity, lead time, safety stock) and gets you a workable order quantity without estimating costs you don't measure.

Once you have a quantity, turn it into an actual order — see the Shopify purchase orders guide for creating and sending one.

Frequently Asked Questions

What is reorder quantity?

Reorder quantity is how many units to order once your reorder point has told you it's time to place an order. It's the "how much" question, separate from the reorder point's "when" question, though both use similar inputs.

How do you calculate reorder quantity?

Reorder quantity = target stock level − (stock on hand + stock on order). Take the total you need to reach your next planned purchase, subtract what you already have on the shelf and what's already coming, and the remainder is what to order now.

Is reorder quantity the same as EOQ?

No. EOQ (Economic Order Quantity) minimizes ordering and holding costs using a formula that assumes constant demand and a fixed lead time: assumptions a seasonal or promo-driven small-store SKU usually breaks. The target-stock-level approach above uses inputs a small merchant actually tracks instead of estimated cost figures.

What happens when a supplier's MOQ is bigger than your calculated reorder quantity?

You order the MOQ, not the calculated number. If your formula says 30 units but the supplier's minimum is 50, you order 50, and the extra 20 units become buffer for a future cycle. That's only a problem if the SKU is slow enough that 50 units represents months of cover; if so, it's worth negotiating a smaller MOQ or sourcing elsewhere.