KPI sandbox — OTIF rate and safety stock, side by side.
Two working planner's scratchpads on one page. Switch tabs to keep each tool open in its own state: results land straight in the KPI Excel template or the SOP pack from the Cratepost shop.
Inputs
Plug in the four numbers.
Safety Stock = z × σd × √L — the textbook σ-based formula. We also show the practitioner shortcut z × D̄ × √L and the simpler no-buffer D̄ × L demand figure for context.
Units sold or consumed per day.
Typical day-to-day swing, in units.
Days from PO to receipt. Minimum 0.5.
1.65 ≈ 95%, 2.33 ≈ 99%.
Defaults mirror the safety-stock blog worked example — 50 u/day · σ 12 · 7 d · z 1.65.
Recommended buffer
σ-based
Safety stock at z = 1.7 (95% service level) — σ_demand = 12· lead time = 7 d · avg = 50 u/day.
52.4units
Buffer protects against 52.4 units of demand variability over the lead-time window. Reorder when on-hand drops to 402.4 units.
z × D̄ × √L practitioner shortcut: 218.3 units · no-buffer D̄ × L: 350 units.
Avg daily demand
50 u/day
Demand std dev
12 σ
Lead time
7 days
z-score
1.7 σ
Safety stock
52.4 units
Practitioner
218.3 units
Demand in LT
350 units
Reorder point
402.4 units
Demand profile
How the five numbers stack up.
Daily demand, demand during lead time, the practitioner-shortcut buffer, the textbook σ-based safety stock, and the reorder point that triggers the next PO.
At z 1.65, you have a friction-fit buffer against multi-week demand surges. Demand has moderate week-to-week variability, so the σ-based buffer is doing useful work. With a typical 7-day lead time, the buffer is sized around a standard reorder cadence.