Reorder Quantity: Simple Formula and Clear Examples

Reorder quantity is one of the most useful tools for keeping your inventory in check. If you run out of stock, you lose sales. If you order too much, you tie up cash and storage space. Getting it right means knowing exactly how much product to reorder and when.

That’s where the reorder quantity formula comes in. It helps you decide the right number of units to buy from your supplier so you don’t overstock or run out. The goal is to stay ready for demand without spending more than you need to.

You’ll learn what reorder quantity is, the formula to calculate it, and how to use it to keep your inventory levels steady. Whether you manage a few products or hundreds of SKUs, this guide will help you make smarter reordering decisions.

What Is Reorder Quantity?

Reorder quantity is the number of units you choose to buy when it’s time to restock. It’s the amount you send to your supplier so you can refill your inventory before it runs out.

The goal is to order just enough, not too much, and not too little. If you order more than you need, you tie up cash and pay more for storage. If you order too little, you risk selling out before new stock arrives.

Reorder quantity helps you find that balance. It’s based on how fast your products sell and how long it takes to get new inventory. When used correctly, it keeps your shelves stocked and your business moving without overspending.

This is different from the reorder point, which tells you when to place an order. Reorder quantity tells you how much to order. Both work together to help you avoid stockouts and overstock.

Reorder Quantity Formula

The reorder quantity formula is simple:

Reorder Quantity = Average Daily Usage × Average Lead Time

This tells you how many units to reorder based on how fast your product sells and how long it takes to restock.

For example, if you sell 15 units per day, and your supplier takes 20 days to deliver, your reorder quantity is:

15 × 20 = 300 units

This means you should reorder 300 units when your stock hits the reorder point. That way, you’ll have enough inventory to last until the new shipment arrives.

If you’re planning a sale or expect a spike in demand, you may need to increase your reorder quantity. The formula is flexible, and it should reflect your current sales pace and supplier timelines.

How to Calculate Reorder Quantity in 3 Quick Steps

Calculating reorder quantity doesn’t have to be complicated. Just follow these three steps:

Step 1: Find Your Average Daily Usage (ADU)

Look at how many units you sell per day. Use recent sales data to get a clear average. A 30-day period is a good starting point, but you can adjust it depending on seasonality or upcoming sales.

Example: If you sold 600 units in the past 30 days, your ADU is 600 ÷ 30 = 20 units per day.

Step 2: Find Your Average Lead Time (ALT)

This is how many days it takes to receive new inventory after placing an order. Count the days from the time you order to the day stock is ready for use or sale.

Example: If it takes 18 days from order to delivery, your ALT is 18 days.

Step 3: Multiply ADU × ALT

Once you have both numbers, multiply them to get your reorder quantity.

Example:
ADU = 20 units
ALT = 18 days
Reorder Quantity = 20 × 18 = 360 units

This means you should order 360 units when it’s time to restock.

Tip: Recheck your numbers often—especially if your sales change or lead times shift. A small change can make a big difference in staying in stock without overspending.

When to Adjust Your Reorder Quantity

Reorder quantity isn’t set in stone. It should change as your business changes.

Here are the most common times to update it:

During sales spikes

If you’re running a promotion, launching a new product, or expecting more traffic, your sales will likely go up. Increase your reorder quantity so you don’t run out of stock early.

During seasonal demand

Certain times of the year—like holidays or back-to-school—may drive higher sales. Use past data to estimate demand and adjust your numbers ahead of time.

When lead times change

If your supplier starts taking longer (or shorter) to deliver, your reorder quantity should change too. A longer lead time means ordering more units to cover the delay.

When product velocity shifts

If a product starts selling faster or slower than usual, update your average daily usage. That way, your reorder quantity stays accurate and reflects real demand.

Checking your reorder quantity regularly helps you keep inventory levels just right, so you’re not overstocked or at risk of running out.

Reorder Quantity vs. Reorder Point (Briefly)

Reorder quantity and reorder point are often confused, but they’re not the same.

• Reorder quantity is the number of units you order when it’s time to restock.
  
• Reorder point is the stock level that tells you it’s time to place that order.
  

Think of it this way:
When your inventory hits the reorder point, it’s your signal to reorder. The reorder quantity tells you how many units to buy.

You need both to keep your inventory flowing smoothly. Reorder points prevent stockouts. Reorder quantities help you order the right amount each time.

For a deeper breakdown of reorder points, check out our dedicated article on how to calculate them.

Benefits of Using Reorder Quantity

Reorder quantity helps you stay in control of your stock. It brings structure to your restocking process and keeps your operations running smoothly.

Here’s how it helps:

Avoid stockouts

Running out of stock means missed sales and disappointed customers. Reorder quantity helps make sure you have enough inventory on hand until the next shipment arrives.

Lower storage costs

When you only order what you need, you avoid overstocking. That means less money tied up in extra stock and less space wasted in your warehouse.

Improve cash flow

Ordering the right amount keeps your inventory lean. You’re not spending more than you need, and your capital stays available for other parts of the business.

Make data-driven decisions

With a clear formula, you’re not guessing. You base restock decisions on real numbers—sales trends and lead times—so your supply matches your demand.

Support growth

As your business grows, managing inventory gets harder. Reorder quantity gives you a repeatable process that scales with you.

Automating the Process

As your order volume grows, tracking reorder quantity manually gets harder. That’s where automation helps.

Inventory management software can calculate reorder quantities for each SKU, alert you when stock hits the reorder point, and even generate purchase orders. This saves time, reduces human error, and keeps your stock levels accurate.

You also get real-time data on sales trends, lead times, and stock movements. With these insights, you can adjust reorder quantities quickly as your business changes.

If you’re working with a fulfillment partner or using multiple warehouses, automation makes it easier to manage everything from one dashboard—no spreadsheets, no guesswork.

Automation helps you stay stocked, lean, and focused on growth.

Conclusion

Reorder quantity gives you a simple way to manage inventory with confidence. By using the formula—Average Daily Usage × Average Lead Time—you can stay ahead of stockouts, reduce waste, and keep your operations running smoothly.

It’s not just about ordering more products. It’s about ordering the right amount at the right time, using data you already have. Whether you’re managing a few SKUs or scaling fast, setting the right reorder quantity helps you plan better and grow smarter.

Review your numbers often, adjust as needed, and consider using inventory software to automate the process. The more accurate your inputs, the better your results.

With reorder quantity in place, you’ll spend less time worrying about inventory and more time focusing on your customers.