EOQ Calculator: Find the Order Size With the Lowest Total Cost
Every order you place costs money to process, ship, and receive. Every unit you store costs money to keep. Order small and often, and the order fees pile up. Order big and rarely, and storage eats your margin. This free EOQ calculator finds the order size where the two costs balance, so your total cost is as low as it can be.
Your numbers
Your result
What the EOQ calculator tells you
Your EOQ is the number of units to buy each time you restock. Get it right and you spend less on both ordering and storage. This economic order quantity calculator gives you four numbers you can act on straight away.
How many to buy
The best order size is the number of units to put on each purchase order. Round it to the nearest case or pallet your supplier ships in.
How often to buy
Orders per year and days between orders turn the result into a simple buying rhythm. That makes it easy to plan your cash and your team's time.
What it costs
Total yearly cost adds your ordering costs and storage costs at the best order size. Any other order size costs more, as the chart shows.
A worked example
A hardware store sells 5,000 boxes of screws a year. Each order costs $50 to place and receive. Storing one box for a year costs $5. The EOQ calculator says the best order size is about 316 boxes, placed around 16 times a year, or every 23 days.
The table shows why. Ordering 100 boxes at a time means 50 orders a year, and the order fees alone hit $2,500. Ordering 1,000 boxes means just 5 orders, but the store pays $2,500 a year to keep the extra boxes on the shelf. At 316 boxes, the two costs are equal and the total drops to about $1,581. That's a saving of more than $1,100 a year on one product.
| Order size | Orders per year | Ordering cost | Storage cost | Total cost |
|---|---|---|---|---|
| 100 boxes | 50 | $2,500 | $250 | $2,750 |
| 200 boxes | 25 | $1,250 | $500 | $1,750 |
| 316 boxes (best) | 15.8 | $791 | $791 | $1,581 |
| 500 boxes | 10 | $500 | $1,250 | $1,750 |
| 1,000 boxes | 5 | $250 | $2,500 | $2,750 |
Finding your three inputs
You don't need perfect numbers. Close estimates still give a useful answer, because small errors in the inputs only shift the result a little. Here's where to look.
Yearly sales
Check your sales reports for the last 12 months. If the product is new or growing fast, use a forecast instead.
Cost per order
Add the time spent creating and checking the order, any flat shipping fee, and the time to receive and shelve the goods.
Cost to store a unit
Include rent for the space, insurance, damage and loss, and the return you could earn on the cash. Many firms use 20% to 30% of the unit's price.
When the answer needs tweaking
Suppliers may have minimum orders or bulk discounts. Use the result as a starting point, then adjust to fit those rules.
When to use a reorder quantity calculator like this
This tool works best for products with fairly steady sales across the year. Think of everyday items like packaging, spare parts, cleaning supplies, or staple stock in a shop. Use it when you set up a new supplier, when prices or fees change, or once a year as a check-up. For seasonal or fast-changing products, run the reorder quantity calculator for each season instead of the whole year. That keeps your order sizes in line with real demand.
Many buyers also use a reorder quantity calculator when they move a product to a new supplier. The order fee, shipping cost, and pack sizes often change, and so does the best order size.
One more tip: the EOQ calculator answers how much to buy. It doesn't tell you when to buy. Pair it with a trigger level based on your sales and delivery times, so each order goes out at the right moment and in the right size.
Common mistakes to avoid
The math is simple, so most errors come from the inputs. Watch out for these when you use the EOQ calculator.
Leaving out hidden order costs
Staff time counts. If someone spends an hour on each order, checking stock, emailing the supplier, and unpacking boxes, that time belongs in your cost per order.
Counting only rent as storage
Rent is just one part. Insurance, damage, theft, and the cash locked in stock all add to the cost of keeping a unit for a year. Leaving them out makes big orders look cheaper than they are.
Never updating the numbers
Sales grow, fees rise, and rent goes up. An order size that was right two years ago may now cost you money. Check it at least once a year.
Frequently asked questions
Quick answers about using this tool. For the theory behind it, read our plain-English guide.
What does an EOQ calculator do?
It finds the order size that keeps your total yearly cost of ordering and storing a product as low as possible. It also shows how many orders that means per year and how many days to leave between them.
Is an economic order quantity calculator the same thing?
Yes. EOQ is just the short name. An economic order quantity calculator and an EOQ calculator do the same job and give the same answer.
How is the best order size worked out?
The tool multiplies 2 by your yearly sales and by your cost per order. It divides that by the cost to store one unit for a year. Then it takes the square root. The result is the order size where ordering and storage costs are equal.
What if my supplier has a minimum order?
Order the larger of the two numbers. If the minimum is much higher than your result, ask whether the supplier offers smaller packs, or check if the per-unit savings make the bigger order worth it.
Can I use this as a reorder quantity calculator for many products?
Yes, but run it for each product on its own. Every product has its own sales, order costs, and storage costs, so each one has its own best order size.
Does InventorysHub work out order sizes for me?
InventorysHub stores the order size you choose for each product and fills it into new purchase orders, so your team orders the right amount every time.