What is the difference between reorder point and reorder quantity?
The reorder point is the inventory level that triggers an order (when to buy). The reorder quantity is how many units to buy once that trigger fires. You need both: one without the other leaves you ordering at the wrong time or in the wrong amount.
How do I calculate reorder quantity?
Start with the demand you need to cover until your next planned order arrives, add your safety stock, and subtract units already in transit. Then adjust to your supplier's minimum order quantity and the cash and storage you have. The economic order quantity formula gives the cost-efficient target before those adjustments.
Andrew Erickson is the founder of Inventory Hero. He has spent years working with Amazon FBA sellers on demand forecasting, restock planning, and the cash flow side of running a private-label brand. Inventory Hero exists because every spreadsheet-based inventory system he tried eventually broke — usually right before Q4.
No. It moves with sales velocity, lead time, and season. A SKU heading into its peak needs a larger reorder quantity than the same SKU in its slow months, which is why a fixed reorder amount quietly causes both stockouts and overstock.
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Reorder quantity is the number of units you order once a SKU hits its reorder point. The short version: order enough to cover demand from now until your next planned order arrives, add your safety stock, and subtract anything already in transit, then adjust to your supplier's minimum order quantity and the cash you have. Below is the working method, the more precise economic order quantity behind it, and a worked FBA example.
The practical formula most FBA sellers actually use is:
Reorder quantity = (demand until the next order lands) + safety stock - units already in transit
The first term is your sales velocity multiplied by the time between this order arriving and the next one. The second is your buffer. The third keeps you from double-ordering stock that is already on the water. The result is the working target before you adjust for real-world limits.
Say a SKU sells 15 units a day, you reorder on a roughly 60-day cycle, you carry 150 units of safety stock, and you already have 200 units inbound:
Input
Value
Daily sales velocity
15 units
Days to cover until next order
60
Safety stock
150 units
Already in transit
200 units
Reorder quantity = (15 x 60) + 150 - 200 = 850 units. Then you sanity-check it: if your supplier's MOQ is 1,000, you order 1,000. If you only have cash for 600 this cycle, you order 600, which simply covers fewer days, so your next reorder point fires sooner (that is what "shortening the cycle" means). Your cycle length is not a number you pick from the air: order your EOQ and the cycle is roughly that quantity divided by velocity, so a 600-unit order at 15 a day is about a 40-day cycle. The formula gives the target; your MOQ and cash set the real number.
The formula above tells you how much you need. The economic order quantity (EOQ) tells you how much is efficient to order at once. EOQ balances two costs that pull in opposite directions: the cost of placing and receiving an order, and the cost of holding the resulting inventory.
Order in large batches and you place fewer orders but carry more cycle stock and more holding cost, including FBA storage. Order in small batches and you save on holding but pay ordering costs more often and risk thinner cover. EOQ finds the batch size where those two costs are lowest combined. See EOQ explained for Amazon sellers for the formula, or run it in the EOQ calculator.
In practice your reorder quantity is the EOQ nudged up to meet your supplier MOQ and down to fit your cash and storage limits. The math gets you close; the constraints set the final number.
A reorder quantity built in a spreadsheet still has to survive three Amazon realities:
Restock and capacity limits. If Amazon caps how much you can send in, your reorder quantity may be limited by space, not demand. Prioritize the cap for SKUs that actually convert.
Storage cost on the batch. A bigger order means more units sitting in FBA paying monthly storage, and risking the aged-inventory surcharge if the SKU slows.1 The holding-cost side of EOQ is not abstract on Amazon; it is a real monthly bill.
Lead time and its variability. The longer and less predictable your lead time, the more cover each order has to carry, which pushes reorder quantity up. See lead time variability and reorder math.
A fixed reorder amount is one of the quietest causes of both stockouts and overstock. The right quantity moves with velocity and season: a SKU heading into Q4 needs a larger order than the same SKU in its slow months. Recalculate it on current velocity each cycle rather than reusing last quarter's number. For the full system this sits inside, see Amazon FBA restock planning, and pair it with when to reorder: the signals sellers miss.
To calculate reorder quantity, cover demand until your next order lands, add safety stock, subtract what is in transit, then adjust to your MOQ, cash, and storage. Use EOQ to find the efficient batch size, and recalculate on real velocity every cycle. Order quantity and reorder point together are the whole restock decision: when, and how much.