What is economic order quantity (EOQ)
Economic order quantity (EOQ) is the unit quantity per order that minimises total inventory cost — the combined sum of ordering costs (what you pay to place and receive each order) and holding costs (what you pay to store inventory between orders). It doesn’t minimise either cost in isolation. It finds the quantity where costs are lowest.
Why businesses use EOQ
Without a model, founders tend toward one of two defaults: large batches, chasing volume pricing, or small orders, keeping cash free. Both cost more than a calculated middle ground. The EOQ model gives you a specific, defensible order size anchored in your actual cost structure — one you can put on a PO, share with a supplier, and audit when costs shift.
What is the economic order quantity formula
The EOQ formula is EOQ = √(2DS / H)
The EOQ calculation is simple: Take your annual demand, multiply it by 2, then multiply that by the cost of placing one order. Divide that number by your annual holding cost per unit, and take the square root. That is units per order.
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Understanding the EOQ variables
Annual demand (D)
This is the total number of units you sell or consume in a year. Use actual sales data, not projections, and adjust seasonally if your demand spikes — for example, if you move 4,000 units in November and December alone out of 10,000 annually.
Ordering cost (S)
This is the cost of placing and receiving a single order — freight, supplier processing fees, and your team's time. If each purchase order costs your business SGD $75 in total administrative and logistics costs, that's your S value.
Holding cost (H)
It's also called the EOQ formula's carrying cost. This is what it costs to hold one unit in inventory for a full year — warehousing, insurance, obsolescence risk, and the opportunity cost of the cash tied up. Carrying cost typically runs between 20% and 30% of unit value for physical-goods businesses.
Note: If a unit is worth SGD $20 and your carrying rate is 25%, H = SGD $5.
Does the EOQ formula include lead time
No. The standard EOQ formula only calculates the optimal order quantity. It does not account for lead time because lead time affects when you should place an order, not how much you should order.
Instead, lead time is used to calculate your reorder point (ROP). A reorder point tells you the inventory level at which you should place your next order so new stock arrives before you run out.
Without safety stock:
ROP = Average daily demand × Lead time
With safety stock:
ROP = (Average daily demand × Lead time) + Safety stock
In practice, businesses use EOQ and reorder points together. EOQ helps determine the most cost-effective order size, while the reorder point ensures that inventory is replenished at the right time.
How to calculate EOQ
- Determine annual demand
Get sales or usage data over the past 12 months. If you are pre-revenue, apply your best conservative estimate, and then review the calculation after you have some real data. Seasonal products should be weighted by real monthly volume rather than a flat average for the year.
- Calculate ordering costs
Calculate the total costs of placing a single order: inbound freight, customs and brokerage if importing, the time your ops or procurement team spends processing, and any supplier minimum order fees. If that total is SGD $120 per order, utilise that figure.
- Calculate holding costs
Start with your annual warehousing cost per unit, then add insurance, shrinkage, and the opportunity cost of capital. If you're paying 18% annually on a credit line to fund inventory, that's a real carrying cost. Add it to your storage fees and express the total as a cost per unit per year.
- Apply the EOQ formula
Plug your values into √(2DS / H). You can run this in a spreadsheet — the EOQ formula Excel version is simply =SQRT((2*D*S)/H), where D, S, and H reference the cells holding your values. The output is your optimal order quantity in units.
EOQ calculation example
Say you sell 6,000 units per year of a product. Each order costs SGD $90 to place and receive. Holding one unit in your warehouse for a year costs SGD $6.
- EOQ = √(2 × 6,000 × 90 / 6)
- EOQ = √(1,080,000 / 6)
- EOQ = √180,000
- EOQ ≈ 424 units per order
That means placing an order for 424 units, roughly 14 times a year, minimises your total inventory cost. Assuming demand is steady throughout the year, that's about one order every 26 days. Order 200 units, and you're placing orders too frequently. Order 1,000 and you're paying more in carrying costs than you're saving on logistics.
Why economic order quantity matters
Lower inventory carrying costs
The EOQ model directly reduces the amount of cash tied up in inventory. If your current practice is ordering 1,000 units at a time and your EOQ is 400, you're buying 600 extra units with every order. On average, that also means more cash tied up in cycle stock between orders.
Improve purchasing efficiency
When procurement runs on intuition, purchase orders pile up inconsistently, and suppliers get erratic demand signals. EOQ gives your team a repeatable framework — a specific order size tied to real cost data, not whoever had time to place an order that week. For businesses processing 200+ purchase orders per year, that consistency reduces admin load and supplier friction.
Support healthier cash flow
Inventory is one of the largest working capital drains for product businesses. This is particularly relevant for Singapore businesses importing inventory from overseas suppliers, where upfront payments, shipping costs, and longer lead times can place additional pressure on working capital.
Using EOQ means you're not tying up SGD $50,000 in stock when SGD $20,000 worth would cover your cycle. That freed capital covers payroll gaps, early supplier discounts, or seasonal demand spikes without needing a credit line.
If you're balancing numerous suppliers and currencies, that focus on cash flow becomes even more vital. Aspire expense management and payable management tools help founders track purchase commitments, vendor payments, and working capital in one place.
Reduce overstocking and stockout risks
A founder who orders 3,000 units of a product in advance of a promotional push that doesn’t perform. Now they have to deal with overstock costs, such as storage fees, markdowns, and a warehouse full of slow-moving SKUs. EOQ doesn’t eliminate that risk, but it grounds your order size in demand realities, not hope.
Assumptions behind the EOQ model
Demand remains constant
The standard EOQ model assumes demand is stable across the year. That works well for commodity inputs or steady-state subscription products. It works less well if your business has a strong seasonal pattern or if you're still in a high-growth phase where volumes change quarter to quarter.
Ordering and holding costs remain stable
Freight rates change. Warehouse lease renewals shift carrying costs. The EOQ formula uses static inputs, so the output is only as accurate as the cost data you feed it. Treat it as a living number, not a one-time calculation.
Inventory is replenished immediately
The basic EOQ formula with lead time adjustments exists precisely because standard EOQ assumes zero replenishment delays. If you're importing inventory from suppliers in Vietnam, China, or other regional markets, lead times can stretch to several weeks. Your businesses must account for these delays when setting reorder points and planning inventory replenishment.
No quantity discounts exist
EOQ assumes a flat per-unit cost. Many suppliers offer tiered pricing — order 500 units, and you pay SGD $12 each; order 1,000, and you pay SGD $10. In those cases, the raw EOQ number may not be your optimal quantity once discount savings are factored in.
No inventory shortages occur
The EOQ model assumes inventory is replenished before the stock gets exhausted. In practice, companies will carry safety stock to lessen the chance of running out due to demand surges or supply delays.
Limitations of EOQ
Demand can fluctuate
For most businesses, demand is not flat. If you're running promotions around major sales events such as 11.11, 12.12, Black Friday, or Lunar New Year, demand can change significantly from one period to the next. EOQ works better as a baseline than as a hard-and-fast rule. Use it as a guide for your order size, then go up or down depending on your forecast.
Lead times aren't always predictable
Your merchandise doesn’t always arrive when you think it would due to supply chain hiccups, customs delays, and supplier capacity concerns. EOQ doesn't factor in variability in lead time. You need safety stock and a reorder point computation running alongside it.
Bulk discounts may change the optimal order quantity
Say a supplier has a 15% price cut at 1,000 units, and your EOQ is 400. You have to do the math on both sides. Sometimes the discount savings can be more than the extra carrying cost. Sometimes they do not. The EOQ gives the starting point, and the discount decision is another cost comparison.
Real-world inventory is more complex than the model assumes
The EOQ model is a single-product framework. If you carry 200 SKUs with different demand rates, holding costs, and supplier minimum order quantities, you're running 200 separate calculations — and those outputs may conflict with each other logistically. Software helps, but the model still requires clean inputs per SKU.
Applying EOQ in different industries
EOQ in manufacturing
Supply chain EOQ applications in manufacturing focus on raw material inputs. A Singapore-based manufacturer sourcing aluminium sheets from regional suppliers uses EOQ to determine how many sheets to order per batch. The goal is to balance procurement and shipping costs against the cost of holding raw materials in inventory. For manufacturers operating across ASEAN supply chains, EOQ can help improve purchasing efficiency and production planning.
EOQ in retail
A Singapore retailer managing 50 SKUs across seasonal and year-round product categories can calculate EOQ separately for each product line. High-demand essentials may require one order quantity, while slower-moving seasonal items require another. This helps retailers balance inventory costs against limited storage space and working capital constraints.
EOQ in ecommerce
Ecommerce businesses selling through marketplaces and third-party logistics (3PL) providers face a distinct version of the EOQ problem. Inventory may be stored across multiple warehouses, while storage fees increase the longer products remain unsold. In these environments, EOQ helps businesses determine order quantities that support sales demand without unnecessarily increasing storage costs.
EOQ vs. reorder point
What EOQ tells you
EOQ answers: How many units should I order at a time? It's a quantity decision, not a timing decision. It tells you the batch size that minimises your combined ordering and carrying costs.
What a reorder point tells you
The EOQ reorder point, or ROP, answers the question: When should I place the next order? It's calculated based on your average daily demand multiplied by your supplier lead time, plus safety stock. ROP and EOQ work as a pair: EOQ defines the order size, ROP defines the trigger.
Why businesses often use both
Running EOQ without a reorder point means you know how much to order, but not when. Running a reorder point without EOQ means you know when to order but risk ordering the wrong quantity. Together, they give you a complete replenishment system: order X units every time stock drops to Y units remaining.
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EOQ vs. MOQ
EOQ vs MOQ is a common source of confusion. EOQ (economic order quantity) is what your cost model says you should order. MOQ (minimum order quantity) is the minimum quantity your supplier asks you to buy. If your EOQ is 300 units and your supplier’s MOQ is 500, then you will order 500 and incur the extra carrying cost.
For Singapore businesses sourcing from overseas manufacturers, negotiating lower MOQs can help reduce inventory carrying costs while preserving working capital, especially during periods of uncertain demand.
For example, if your EOQ is 300 units but a supplier’s minimum order quantity (MOQ) is 500 units, you will need to decide if the increased carrying costs are worth the supplier pricing, availability, or strategic reasons.
Conclusion
EOQ is one of those tools that looks simple until you try to apply it accurately. The formula takes 30 seconds. Getting the right input data — actual demand, fully loaded ordering costs, realistic carrying rates — takes longer. That's where the value is. Founders who run the numbers with clean inputs find that their current order quantities are often 30–50% off optimal, and the correction pays for itself within a few months in reduced carrying costs and freed-up cash.
Use EOQ as a quarterly exercise, not a one-time setup. As your volumes grow and supplier relationships evolve, your optimal order quantity shifts. Build it into your procurement review cycle alongside your reorder point and safety stock calculations, and you'll have a replenishment system that actually scales.
FAQs
When does EOQ work best?
EOQ is most successful when demand is generally consistent, supplier lead times are predictable, and inventory costs can be forecast with fair precision. For very seasonal demand or fast-changing sales patterns, EOQ alone may not be enough, and other forecasting methodologies may be required by the business.
How do you calculate EOQ?
Multiply 2 by your annual demand (D) and your cost per order (S), divide by your annual holding cost per unit (H), then take the square root. In Excel, enter =SQRT((2*D*S)/H) using cell references for each variable.
Why is EOQ important in inventory management?
The EOQ is a data-driven order quantity that minimises total inventory cost. Without it, most businesses either overstock and tie up cash or understock and pay premium freight on emergency reorders.
What costs does EOQ minimise?
EOQ minimises the sum of ordering costs (fixed cost per order) and holding costs (carrying cost per unit per year). It finds the quantity when the two expenses are the same.
Can EOQ be used when demand fluctuates?
Yes, but with modifications. The classical EOQ model is based on constant demand. If demand varies, use a weighted average demand number and utilise your EOQ with a safety stock calculation to absorb variations. Increase the frequency of EOQ recalculation in periods of high growth.
How often should businesses recalculate EOQ?
Recalculate EOQ each quarter or if there is a significant change in demand, supplier pricing, freight rates, or warehousing expenses. Annual calculations are the bare minimum. Quarterly keeps your replenishment model fresh.
Does EOQ account for quantity discounts?
The typical EOQ formula does not consider quantity discounts. For tiered pricing, compare the overall cost at the EOQ quantity to the total cost at each discount threshold, including the extra carrying cost from the larger order, and pick the lowest.
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