Reorder Quantity Formula: How Much Inventory Should You Order?

Reorder quantity is the number of units you buy when replenishment is triggered. It answers “how much should I order?” Reorder point answers a different question: “when should I order?”

Simple reorder quantity formula

For a target-stock or min-max system, a practical formula is:

Reorder Quantity = Target Stock Level − Inventory Position

Inventory position should reflect the stock that is realistically available to cover demand. A useful operating definition is:

Inventory Position = On-Hand Inventory + Reliable On-Order Inventory − Committed Demand

Reorder quantity example

Assume a retailer wants a target stock level of 120 units. It currently has:

• 40 units on hand
• 20 units already on a reliable purchase order
• 5 units committed to customer demand

Inventory position is:

40 + 20 − 5 = 55 units

The reorder quantity is:

120 − 55 = 65 units

Before placing the order, the buyer should still check supplier minimums, case packs, shelf life, storage space, and budget.

Reorder quantity vs reorder point

Metric	Question answered	Typical inputs
Reorder point	When should I order?	Demand during lead time + safety stock
Reorder quantity	How much should I order?	Target level, inventory position, supplier and storage constraints

The standard reorder-point formula is:

Reorder Point = Average Daily Demand × Lead Time + Safety Stock

See the full reorder point guide.

Method 1: target-stock reorder quantity

This is often the easiest method for small and midsize physical businesses. Set a target inventory level that reflects expected demand, lead time, safety stock, and your preferred review cycle. When replenishment is triggered, order enough to restore inventory position toward the target.

This method is especially practical when supplier constraints and demand patterns matter more than mathematically minimizing ordering cost.

Method 2: min-max reorder quantity

In a min-max system, the minimum level usually acts as the reorder trigger and the maximum level acts as the replenishment target.

Reorder Quantity = Maximum Inventory Level − Current Inventory Position

If the maximum is 350 units and the current inventory position is 150, the reorder quantity is 200 units.

See min-max inventory for the full method.

Method 3: economic order quantity (EOQ)

EOQ estimates an order size that balances modeled ordering and holding costs:

EOQ = √(2DS ÷ H)

• D = annual demand in units
• S = fixed cost per order
• H = annual holding cost per unit

EOQ can be useful when demand is stable, ordering costs are measurable, and products do not have severe shelf-life or capacity constraints. It is less useful when demand is highly volatile or supplier case packs dominate the actual buying decision.

See the EOQ guide.

Reorder quantity is not the same as MOQ

A minimum order quantity (MOQ) is a supplier constraint. Reorder quantity is the amount your inventory plan says you need.

If your calculated need is 65 units but the supplier's MOQ is 100, you must decide whether to buy 100, negotiate the MOQ, combine demand across locations, choose another supplier, or delay the purchase. Do not silently replace demand-driven planning with the supplier's preferred order size.

Factors that should change reorder quantity

Open purchase orders

Do not order the same demand twice. Include inbound inventory only when the order is reliable and expected to arrive in time.

Committed demand

Customer orders, reservations, or other commitments reduce the inventory available for future sales.

Supplier lead time

Longer or more variable lead times may require a higher target inventory position.

Supplier MOQ and case packs

You may need to round a calculated order to a carton, case, pallet, or supplier minimum.

Storage capacity

A mathematically valid order can still be operationally impossible if it does not fit the location.

Shelf life and obsolescence

Perishable and trend-sensitive products should not be replenished to the same coverage targets as stable nonperishables.

Seasonality and promotions

Historical averages can understate demand before a peak or overstate it after a promotion.

Transfers from other locations

Surplus at another store may satisfy demand faster and more cheaply than a new supplier order.

How lead time and safety stock affect order size

Lead time primarily affects when the reorder is triggered, but it can also affect the target inventory level used to calculate order size. If replenishment is slow or unreliable, the business may need more coverage.

Use actual supplier performance where possible instead of relying only on quoted lead times. See inventory lead time and safety stock.

Reorder quantity for multiple locations

Do not calculate a companywide quantity and divide it equally across stores. Demand, shelf capacity, supplier access, and existing stock can vary significantly by location.

A better process is:

1. Calculate inventory position by location.
2. Estimate each location's target stock.
3. Check whether another location has excess inventory.
4. Use transfers where practical.
5. Combine the remaining supplier demand if centralized purchasing creates better terms.

See multi-location inventory management.

Common reorder quantity mistakes

• Ignoring inventory already on order
• Using on-hand stock without subtracting committed demand
• Ordering the same fixed quantity for every SKU
• Letting supplier MOQ become the inventory strategy
• Ignoring shelf life and storage limits
• Using annual averages for strongly seasonal products
• Failing to recalculate targets after lead-time changes
• Buying new stock when another location already has excess

How reorder quantity fits into a replenishment system

A complete replenishment workflow combines:

• demand forecasting
• reorder points
• safety stock
• inventory position
• reorder quantity
• supplier constraints
• purchase orders
• receiving

See inventory replenishment methods and best practices.

How Stash helps

Stash inventory management software brings stock, sales context, suppliers, purchase orders, forecasting, lead times, and multiple locations into one workflow. That helps teams calculate replenishment needs with a clearer view of what is on hand, what is already on order, and where demand is occurring.

Frequently asked questions

What is the simplest reorder quantity formula?

A practical starting point is target stock level minus inventory position. Inventory position should account for on-hand stock, reliable inbound inventory, and committed demand.

Is reorder quantity the same as reorder point?

No. Reorder point tells you when to order. Reorder quantity tells you how much to order.

Should open purchase orders reduce reorder quantity?

Usually yes, if those orders are reliable and will arrive in time. Otherwise you risk duplicate purchasing.

What if my supplier MOQ is higher than my calculated reorder quantity?

Compare the cost of excess inventory with alternatives such as negotiating the MOQ, combining demand, transferring inventory, or using another supplier.

How often should reorder quantities be recalculated?

Review them whenever demand, lead time, supplier terms, shelf life, storage capacity, or location behavior changes materially.

Next steps

First set a reliable reorder point, then choose the order-size method that fits your operating model. For ongoing purchasing, continue with inventory replenishment and open-to-buy planning.