How to understand economic order quantity

Definition

Economic order quantity is the purchase size that keeps ordering cost and holding cost as low as they can be together. On the books, this is a buying-size rule, not an account named EOQ.

Each order you place costs time and fees. Each unit you hold costs space, insurance, and tied-up cash.

The quantity you pick sits between those two pressures. Too small, and you order constantly; too large, and the stockroom stays full.

This number tells you how many units to put on a purchase order. It does not tell you which day to send it.

Where it shows up

Balance Sheet: Related to the inventory line, which is larger when orders are bigger.

P&L: Related to ordering and holding costs, not to a named EOQ account.

See also: Reorder Point · Inventory · Purchase Order

When you look at your Balance Sheet, EOQ is not a line. Bigger orders leave more inventory in current assets between deliveries.

The profit and loss statement does not say EOQ. You will see freight, labor to place orders, storage, and similar costs, which this rule is trying to keep down as a pair.

Cash does not move when you calculate the number. Cash moves when you pay for a purchase of that size.

A shop that always orders a huge pile will show a heavier inventory balance. A shop that orders tiny piles will show a lighter one, and will place orders more often.

How it works

You estimate how many units you will need over a year. You also estimate what it costs to place one order, and what it costs to hold one unit for a year.

Ordering cost includes time, paperwork, and inbound fees that hit per order rather than per unit. Holding cost includes space, insurance, spoilage risk, and cash sitting in stock.

The classic picture balances those two. As order size rises, you place fewer orders and ordering cost falls, while holding cost rises because average stock is higher.

The quantity in the middle is the economic order quantity. It is a planning number you then put on a purchase order.

Vendor wait time does not set this size. That wait belongs to when you order; this rule belongs to how many you order.

Freight that rides with each order can change the math if it is truly a per-order cost. If freight is per unit, it belongs with unit cost instead.

When the goods arrive, you receive them at cost like any other buy. You debit inventory and credit accounts payable, not an EOQ account.

You can still order a different size when a season changes. The formula is a starting point, not a lock on every purchase order.

Example

A shoe store sells about 800 pairs of a school sneaker each year. It costs about $25 to place one order with the brand, and about $4 a year to hold one pair in the back room.

A common way to pick the size is to take annual unit demand, multiply by twice the cost of one order, divide by the cost of holding one unit for a year, and take the square root. For this shop that comes out to 100 pairs.

Each pair costs the store $30, so a 100-pair order is $3,000. When the cartons arrive on credit, the store records:

Debit: Inventory $3,000

Credit: Accounts payable $3,000

Inventory goes up by $3,000. There is no EOQ account on that entry.

The Balance Sheet is larger on both sides until the sneakers sell. Ordering 100 pairs at a time, rather than 20 or 400, is the size this shop chose to keep combined ordering and holding costs down.

If they ordered 20 pairs each time, they would place many more orders. If they ordered 400, the stockroom and the inventory line would stay heavy for months.

Common mix-ups

Economic order quantity is not the reorder point. EOQ is how many to buy; the reorder point is when to buy.

EOQ is not a general-ledger account. The size only shows up later as ordinary inventory when the order arrives.

EOQ is not a promise that demand will stay flat. It is a planning size; you can still order sooner or later if sales change.

Related terms

• Reorder Point: The stock level that triggers a new purchase order.
• Safety Stock: Extra inventory held as a buffer against demand or supply swings.
• Inventory: Goods held for sale or used to produce goods for sale.
• Purchase Order: The document authorizing a purchase from a vendor at agreed terms.
• Inventory Turnover: How many times inventory is sold and replaced in a period.
• Landed Cost: The full cost of getting a purchased item to your door, including freight and duties.
• Days Inventory Outstanding: The average number of days inventory sits before it sells.
• Working Capital: Current assets minus current liabilities, showing short-term operating cushion.