Calculating Economic Order Quantity to Optimize Inventory Costs

Every business that buys and stores materials faces the same tension: order too little, and you’re placing orders constantly, racking up administrative and shipping costs. Order too much, and your money is tied up in stock sitting on a shelf. Economic Order Quantity (EOQ) is the formula that resolves this tension – it tells you exactly how much to order at a time to keep your total inventory costs as low as possible. Originally developed by Ford W. Harris in 1913, the EOQ model has remained a foundational tool in inventory management for over a century, and it’s just as relevant for a small craft enterprise as it is for a large manufacturer.

What is economic order quantity (EOQ)? 🔗

At its core, Economic Order Quantity is the ideal number of units a business should order at one time to minimize two competing costs: the cost of placing orders and the cost of holding inventory. These two costs move in opposite directions. When you order in large batches, you place fewer orders per year, so ordering costs go down – but your average stock level rises, pushing holding costs up. When you order in small batches frequently, holding costs drop – but you’re placing more orders and spending more on each ordering cycle. EOQ finds the sweet spot where the sum of both costs is at its lowest.

According to the EOQ model, this calculation works best when annual demand is relatively stable and consistent, each order is delivered in full, and costs per order and per unit remain constant over the period being measured. These assumptions make EOQ especially practical for businesses that deal in standardized raw materials with predictable usage – exactly the kind of inputs common in micro-enterprises like handcraft production.

Two types of costs EOQ addresses 🔗

Ordering costs are the expenses incurred every time a purchase order is placed – regardless of how many units are in that order. These include the time spent creating and processing the order, communication with suppliers, transportation or delivery charges, and inspection of received goods. The more frequently you order, the higher your total annual ordering costs.

Carrying costs (or holding costs) are the expenses of storing inventory over time. As explained by EazyStock, these include storage space, rent, insurance, deterioration of materials, and the opportunity cost of capital tied up in stock. The more inventory you hold at any given time, the higher these costs climb.

The EOQ formula 🔗

The standard EOQ formula is straightforward:

EOQ = √ (2DS / H)

Where:

D = Annual demand (total units required per year)
S = Ordering cost per order (cost incurred each time an order is placed)
H = Holding/carrying cost per unit per year (cost to store one unit for one full year)

The result gives you the optimal order quantity – the number of units you should order each time you restock a particular material. As CFI notes, this formula is derived by minimizing the total annual cost function – the point where the ordering cost curve and the holding cost curve intersect is the EOQ.

Balancing order size and carrying costs 🔗

The relationship between order size and cost is inverse and interdependent. If you increase your order quantity, you need to place fewer orders annually, so your ordering costs fall. But a larger order also means more inventory sitting in storage at any time, which raises your carrying costs. If you reduce your order quantity, you order more frequently and carrying costs fall – but ordering costs increase. NetSuite explains that this tension means businesses that don’t calculate EOQ often end up unknowingly over-ordering or under-ordering, both of which erode profitability.

EOQ resolves this by mathematically identifying the exact quantity where total cost – the sum of ordering and carrying costs – is at its minimum. It doesn’t minimize either cost in isolation; it minimizes both together. This is what makes it a genuinely useful decision tool rather than a rough estimate.

What ordering frequency follows from EOQ? 🔗

Once you know your EOQ, you can calculate how many orders to place per year using this formula:

Number of orders per year = Annual demand (D) ÷ EOQ

And the time between orders:

Time between orders = Working days in a year ÷ Number of orders per year

These follow-on calculations help translate the EOQ figure into a concrete restocking schedule, which is particularly useful for micro-enterprise owners managing multiple raw materials simultaneously.

Total minimum cost calculation 🔗

You can also verify that your EOQ is correct by computing the total annual inventory cost at that quantity:

Total Cost = (D/EOQ) × S + (EOQ/2) × H

The first term is the total annual ordering cost; the second is the total annual holding cost. At the EOQ quantity, these two terms will be equal to each other – a useful check to confirm your numbers are right.

Practical application of EOQ in micro-enterprises 🔗

For a small or micro-enterprise – a home-based craft business, a small food producer, a local artisan workshop – the EOQ formula is one of the most accessible ways to introduce cost discipline into purchasing decisions. CIPS notes that smaller businesses face particular financial and logistical limitations in managing inventory, making it critical to choose the most effective method for their situation. EOQ gives small business owners a data-driven answer to a question they often answer by instinct: how much should I order this time?

Let’s work through two realistic examples drawn from a micro-enterprise that produces handcrafted jute bags and dyed fabric goods – a business that relies on jute string and synthetic colors as core raw materials.

Example 1: EOQ for jute string 🔗

Suppose a small jute bag enterprise uses jute string throughout the year. Here are the known figures:

Annual demand (D): 1,200 kg
Ordering cost per order (S): ₹300
Carrying cost per kg per year (H): ₹6

Applying the EOQ formula:

EOQ = √ (2 × 1,200 × 300 / 6)
= √ (720,000 / 6)
= √ 120,000
= 346 kg (approximately)

This means the enterprise should order approximately 346 kg of jute string per order to minimize total inventory costs.

Number of orders per year = 1,200 ÷ 346 ≈ 3.47 orders, or roughly one order every 3.5 months.

Total annual cost at EOQ:
= (1,200/346) × 300 + (346/2) × 6
= ₹1,040 + ₹1,038
= ≈ ₹2,078

Notice that ordering cost and carrying cost are nearly equal at the EOQ – this is always the case, and it’s how you verify the calculation is correct.

Example 2: EOQ for synthetic colors 🔗

The same enterprise also uses synthetic colors for dyeing. These are more expensive to store (they require dry, temperature-controlled conditions) and are ordered more frequently due to higher usage.

Annual demand (D): 600 units (bottles)
Ordering cost per order (S): ₹250
Carrying cost per unit per year (H): ₹10

Applying the EOQ formula:

EOQ = √ (2 × 600 × 250 / 10)
= √ (300,000 / 10)
= √ 30,000
= 173 units (approximately)

So the enterprise should order approximately 173 bottles of synthetic color per order.

Number of orders per year = 600 ÷ 173 ≈ 3.47 orders, or roughly once every 3.5 months.

Total annual cost at EOQ:
= (600/173) × 250 + (173/2) × 10
= ₹867 + ₹865
= ≈ ₹1,732

Again, the near-equal split between ordering and holding costs at this quantity confirms the EOQ is correctly calculated.

What these calculations tell the business owner 🔗

For both materials, the EOQ model reveals an ordering rhythm that the business owner can build into a calendar. Rather than guessing when to reorder or responding reactively when stock runs low, they now have a specific quantity and approximate schedule for each material. This prevents both overstocking – which ties up cash in slow-moving inventory – and stockouts, which can halt production entirely.

As Unleashed Software points out, EOQ is especially important for any business trying to reduce overall inventory costs while still meeting demand. For a micro-enterprise operating on tight margins, even modest savings on carrying and ordering costs across two or three materials can meaningfully improve monthly cash flow.

Assumptions and limitations to keep in mind 🔗

EOQ works best when demand is consistent and predictable. If a business faces seasonal spikes – for example, higher orders for dyed fabric goods during festival seasons – the standard EOQ formula will underperform during peak periods. In those cases, the model can be adjusted or supplemented with safety stock calculations to create a buffer. MRPeasy notes that EOQ also assumes costs remain fixed throughout the year, which may not reflect real-world price fluctuations from suppliers.

Additionally, supplier minimum order quantities (MOQ) can sometimes be higher than the calculated EOQ, meaning the business has no choice but to order more than the model recommends. In such cases, the EOQ still provides a useful reference point – even if you can’t order exactly that quantity, knowing it helps you negotiate with suppliers or choose between competing vendors based on whose MOQ most closely aligns with your optimal order size.

Despite these limitations, EOQ remains one of the most practical, low-cost tools available to any business managing physical inventory. It doesn’t require software or advanced training – just three accurate data points and a calculator.

What do you think? If you run or manage a small business, how do you currently decide how much raw material to order – and do you think applying the EOQ formula would change that decision? For materials with seasonal demand, what adjustments would you make to the basic EOQ model to account for fluctuating usage throughout the year?

References

1. https://corporatefinanceinstitute.com/resources/accounting/what-is-eoq-formula/
2. https://en.wikipedia.org/wiki/Economic_order_quantity
3. https://www.eazystock.com/uk/blog-uk/calculating-economic-order-quantity-formula/
4. https://www.netsuite.com/portal/resource/articles/inventory-management/economic-order-quantity-eoq.shtml
5. https://www.cips.org/intelligence-hub/operations-management/economic-order-quantity
6. https://www.unleashedsoftware.com/blog/economic-order-quantity-explained-formulas-how-to-use-them/
7. https://www.mrpeasy.com/blog/economic-order-quantity-eoq/