What Is Economic Order Quantity (EOQ)? Formula + When It Actually Applies
EOQ is the order size that minimizes the combined cost of ordering and holding inventory. The formula is simple — the catch is that its assumptions rarely hold for a real multi-channel ecommerce brand. Here's the math and the honest limits.
Quick Answer
Economic Order Quantity (EOQ) is the order quantity that minimizes total inventory cost — the trade-off between ordering too often (high order/setup costs) and ordering too much at once (high holding costs).
Where D = annual demand (units), S = cost per order, H = holding cost per unit per year. Example: D = 12,000, S = $80, H = $3 → EOQ = √(2×12,000×80 / 3) = √640,000 = ~800 units per order. EOQ is a useful starting reference — but it assumes steady demand, fixed costs, and no MOQs or volume discounts, which is why most ecommerce brands use it as a sanity check, not a rule.
How EOQ works, step by step
The two costs EOQ balances
Order more frequently in small batches and your ordering costs (PO processing, inbound, per-shipment fees) climb. Order rarely in big batches and your holding costs (storage, capital, obsolescence, on Amazon the storage + aged fees) climb. EOQ is the quantity where those two curves cross — the lowest total cost.
Plug in the three inputs
D — annual demand in units (use your forecast, not last year blindly). S — the fixed cost to place one order (admin time + inbound/freight + per-shipment fees). H — annual holding cost per unit (storage + cost of capital + risk; often estimated as 20–30% of unit cost). Get H right — it's the input brands most often lowball.
Solve and sanity-check
EOQ = √(2DS/H). With D = 12,000, S = $80, H = $3, EOQ ≈ 800 units. That implies ordering 12,000 ÷ 800 = 15 times a year, roughly every 24 days. Now sanity-check against reality: does your supplier's MOQ allow 800? Is there a volume break at 1,000 that beats EOQ on landed cost? Does 24-day cadence fit your lead time?
Where EOQ breaks for ecommerce
The classic formula assumes constant demand, a fixed order cost, no quantity discounts, no MOQs, and a single location. Real ecommerce violates all five: demand is seasonal and promo-driven, suppliers impose MOQs and tiered pricing, and you're fulfilling across FBA, AWD, Shopify, and Walmart. EOQ gives you a reference point; it does not give you a reorder plan.
EOQ assumptions vs ecommerce reality
| EOQ assumes… | Ecommerce reality |
|---|---|
| Demand is constant + known | Seasonal, promo-driven, varies by channel |
| Order cost is a fixed number | Varies with freight, IPS placement, container fill |
| No minimum order quantities | Suppliers impose MOQs that override EOQ |
| No volume discounts | Tiered pricing often beats EOQ on landed cost |
| One stocking location | FBA + AWD + 3PL + Shopify + Walmart at once |
The honest caveat
EOQ is a 110-year-old formula built for a factory ordering raw materials with steady demand. It's genuinely useful as a mental model — it teaches you that there's a cost-minimizing batch size and that ordering too often or too rarely both cost money. But running your ecommerce reorders straight off EOQ will fight your supplier's MOQs, ignore your Q4 seasonality, and miss the per-channel split. Use EOQ to understand the trade-off; use a demand forecast with real constraints to actually decide order quantities.
Frequently asked questions
What is the economic order quantity (EOQ)?
EOQ is the order quantity that minimizes total inventory cost — the balance between ordering costs (which rise the more often you order) and holding costs (which rise the more you hold). It tells you the cost-optimal batch size under steady-demand assumptions, and is best used as a sanity-check reference rather than a literal reorder rule for ecommerce.
What is the EOQ formula?
EOQ = the square root of (2 × D × S ÷ H), where D = annual demand in units, S = cost per order, and H = holding cost per unit per year. Example: D = 12,000, S = $80, H = $3 → EOQ = √(2×12,000×80/3) = √640,000 = ~800 units per order.
What are the inputs to EOQ?
Three: annual demand (D, in units — use your forecast), the fixed cost to place one order (S — admin time + freight + per-shipment fees), and annual holding cost per unit (H — storage + cost of capital + obsolescence risk, often ~20–30% of unit cost). Holding cost is the input brands most often underestimate, which inflates the calculated EOQ.
What are the limitations of EOQ?
EOQ assumes constant, known demand, a fixed order cost, no minimum order quantities, no volume discounts, and a single stocking location. Real ecommerce violates all five — demand is seasonal and channel-specific, suppliers impose MOQs and tiered pricing, and you fulfill across FBA, AWD, Shopify, and Walmart. So EOQ is a reference point, not a reorder plan.
Should ecommerce brands use EOQ?
As a mental model, yes — it teaches the real trade-off between ordering too often and holding too much. As a literal order-quantity rule, rarely — it will fight your supplier's MOQs and ignore seasonality and per-channel demand. Use EOQ to understand the cost curve, then set actual quantities with a demand forecast that includes your real constraints.
What’s the difference between EOQ and reorder point?
EOQ answers how much to order (the cost-minimizing batch size). The reorder point answers when to order (the stock level that triggers a new PO, = lead-time demand + safety stock). They're complementary: EOQ sizes the order, the reorder point times it. Most ecommerce brands need both, adjusted for real-world constraints. See the reorder-point breakdown here.