Kanban Sizing Calculator & Buffer-policy Worksheet

{ "Title": "Kanban Sizing Calculator & Buffer-policy Worksheet", "IntroductionHtml": "

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.

", "Fields": [ { "Key": "avgDailyDemand", "FieldType": "number", "Label": "Average daily demand (units)", "HelpText": "Typical units consumed or produced per operating day. Use the same unit as container size.", "Required": true }, { "Key": "dailyStdDev", "FieldType": "number", "Label": "Daily demand standard deviation (units)", "HelpText": "Enter the standard deviation of daily demand. If unknown, leave blank and provide CV% instead, or estimate using the guidance above.", "Required": false }, { "Key": "cvPercent", "FieldType": "number", "Label": "Coefficient of variation (CV %) — optional", "HelpText": "Enter a percent (e.g., 25 for 25%). If provided and daily SD is blank, SD will be estimated as avgDailyDemand * (CV/100).", "Required": false }, { "Key": "leadTimeDays", "FieldType": "number", "Label": "Supplier/production lead time (days)", "HelpText": "Number of days between a replenishment trigger and receipt of material.", "Required": true }, { "Key": "reviewIntervalDays", "FieldType": "number", "Label": "Review interval (days)", "HelpText": "How often you review or pull inventory per container (e.g., daily = 1). Use 0 if continuous pull. This affects the in-system quantity needed.", "Required": true, "DefaultValue": 1 }, { "Key": "serviceLevelPercent", "FieldType": "number", "Label": "Desired service level (%)", "HelpText": "Percentage probability you want to avoid stockout during lead time (common choices: 90, 95, 99).", "Required": true, "DefaultValue": 95 }, { "Key": "containerSize", "FieldType": "number", "Label": "Container size (units per kanban container)", "HelpText": "How many units fit in one kanban bin, box, or container.", "Required": true }, { "Key": "rounding", "FieldType": "select", "Label": "Rounding method for containers", "HelpText": "How to convert fractional container counts into whole containers.", "Options": [ { "Value": "up", "Label": "Round up (recommended)" }, { "Value": "nearest", "Label": "Nearest container" }, { "Value": "down", "Label": "Round down (not recommended)" } ], "Required": true, "DefaultValue": "up" }, { "Key": "teamNotes", "FieldType": "textarea", "Label": "Team notes or saved computed results", "HelpText": "Paste your computed safety stock, reorder point, and final kanban container count here, or record decisions and risk checks. Useful for audits and continuous improvement.", "Required": false } ], "SubmitLabel": "Save parameters & notes", "SuccessMessage": "Configuration saved. Use the formulas in the guidance section to compute safety stock, reorder point, and container counts. Paste computed results into the Team notes field if you want them saved with this submission.", "DataType": "kanban_sizing_submission", "SchemaVersion": "1.0" }