Kanban Sizing Calculator & Buffer-policy Worksheet

Purpose

Use this worksheet to capture the numbers your team agrees on, save them for repeatability, and follow clear formulas to size kanban containers and reorder points so you can reduce inventory without increasing stockout risk.

Quick formulas (how the calculator works)

1. Average demand per day = µ (units/day).
2. Daily demand standard deviation = σ (units/day). If you only have coefficient of variation (CV), use σ = µ * CV.
3. Demand variability over lead time: σ_LT = σ * sqrt(lead time in days).
4. Find z for your desired service level (example values below).
5. Safety stock = z * σ_LT.
6. Reorder point (units) = µ * lead time + safety stock.
7. Number of containers (kanban cards) = ceil((µ * (lead time + review interval) + safety stock) / container size).

Common z (normal) values

• 90% → z = 1.28
• 95% → z = 1.645
• 97.5% → z = 1.96
• 99% → z = 2.33

Practical notes

- If you don’t know daily SD, estimate CV: 10–20% low variability, 20–50% medium, 50%+ high. Use CV% as percentage (e.g., 25 → 0.25).

- Always round kanban container counts up to avoid hidden stockouts unless you deliberately accept risk.

- Review cadence: if lead time < 2 days, daily review is common; 2–7 days consider twice-weekly; >7 days consider weekly or align with supplier frequency.

The form below saves the configuration and team notes. Use the formulas above (or paste computed results into the notes field) and save a record of the decision.