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12 guides liveHow do I find the optimal order quantity?
What Is Economic Order Quantity (EOQ)?
A plain-English explanation of EOQ — what it measures, why ordering and holding costs must be balanced, and how to interpret the result.
Read guide →What is the EOQ formula and how is it derived?
The EOQ Formula Explained
A complete walkthrough of the EOQ formula — every variable defined, the derivation shown step-by-step, and a worked example with real numbers.
Read guide →When should I place my next order?
What Is Reorder Point (ROP)?
The reorder point is the inventory level that triggers replenishment. Learn how lead-time demand and safety stock combine to set the right trigger.
Read guide →How do I calculate the reorder point?
Reorder Point (ROP) Formula (With Example)
A complete walkthrough of the ROP formula — every variable defined, four formula variants, and a step-by-step worked example with real numbers.
Read guide →How much buffer inventory do I need?
What Is Safety Stock?
Safety stock is extra inventory held to prevent stockouts from demand and lead-time variability. Learn what drives it and how to calculate it.
Read guide →How do I calculate safety stock?
Safety Stock Formula (With Example)
A complete walkthrough of SS = Z × σd × √LT — every variable defined, z-score reference table, four variants, and a step-by-step worked example.
Read guide →How long does replenishment actually take?
What Is Lead Time?
Lead time is the total time from placing an order to receiving it. Learn what drives it, how it affects your reorder point and safety stock, and common measurement mistakes.
Read guide →How do I calculate total lead time?
Lead Time Formula (With Example)
A complete breakdown of LT = T_op + T_sp + T_tr + T_rc — every stage defined, a worked example, and how lead time feeds into the reorder point and safety stock formulas.
Read guide →How do I know if my stock is moving efficiently?
What Is Inventory Turnover?
Inventory turnover measures how many times you sell and replace your stock in a period. Learn benchmarks by industry, what high vs low turnover means, the DIO relationship, and how to improve your ratio.
Read guide →How do I calculate inventory turnover and DIO?
Inventory Turnover Formula (With Example)
A complete breakdown of COGS ÷ Average Inventory — every variable defined, DIO conversion (365 ÷ Turnover), four formula variants, and a step-by-step worked example.
Read guide →Do I have enough stock to cover my lead time?
What Is Days of Supply?
Days of Supply measures how many days your current inventory will last at your demand rate. Learn the lead time rule, Target DOS formula, DOS vs DIO, and how to reduce excess inventory.
Read guide →How do I calculate Days of Supply and Target DOS?
Days of Supply Formula (With Example)
All formula variants defined — DOS = On-Hand ÷ Daily Demand, the annual demand conversion, Target DOS = Lead Time + Safety Stock Days, and the financial DIO alternative.
Read guide →Coming Soon
Ready to Run the Numbers?
Each guide has a free calculator that does the maths for you — no spreadsheet needed.
Frequently Asked Questions
What is the difference between a definition guide and a formula guide?
Definition guides explain what a concept is, why it matters, and how it fits into a broader inventory management system — they are best read before using a calculator for the first time. Formula guides go one level deeper, walking through the mathematical derivation, every variable, and a step-by-step worked example. Both complement the calculators but serve different needs.
Do I need to read the guides before using the calculators?
No — the calculators include inline help text that explains each input as you enter it. The guides are for when you want to understand the underlying theory: why the formula works, what assumptions it makes, and how to interpret the result in the context of your business.
Where should I start if I am new to inventory management?
Start with What Is EOQ? to understand order-quantity optimisation, then read What Is Reorder Point? to learn when to trigger each order. Together they define a complete replenishment policy. Once you understand both concepts, use the linked calculators to apply them to your own numbers.
Are the formulas in these guides industry-standard?
Yes. All formulas are drawn from standard operations management and supply chain literature. Where there are common variants — such as the EOQ model extended for quantity discounts — the guides note them explicitly and explain when to use each version.