Safety stock calculator for spare parts
How many extra units of a part to keep so a slow delivery or a busy week doesn’t leave a machine waiting, and the reorder point that goes with it.
Your numbers
How fast you use itHow long it takes to arrive See your resultResult
Safety stock 34 units Reorder point 48 unitsorder again when stock falls to this Used during an average delivery 14.0 units Days of cover from safety stock 17.0 Stop working this out by handFleetZap counts parts in and out on every work order and alerts you when stock drops to its reorder point.
See FleetZap Maintenance · Try the demoThe formula
Safety stock = (Most used per day × Longest delivery) − (Average used per day × Average delivery)
This is the max-minus-average method, which needs no statistics and suits spare parts. With the defaults: (4 × 12) − (2 × 7) = 34 units, and a reorder point of 2 × 7 + 34 = 48. The spare parts inventory guide covers which parts deserve it.
Using the numberWhat to do with it
- Keep safety stock on parts whose shortage stops a machine; for the rest, a lower buffer or none frees up cash.
- Use real numbers from the last 6 to 12 months of work orders and deliveries, not guesses.
- Review it when a vendor’s delivery time changes: lead time drives the result more than usage.
Guides behind this calculator
Spare parts inventory Parts inventory software Parts kitting for maintenanceMore free calculators
Downtime cost calculator MTBF calculator OEE calculator Equipment cost per hour calculator Equipment depreciation calculator Equipment rental rate calculator Next PM due calculator EOQ calculator Reorder point calculatorFleetZap Maintenance
The heart of FleetZap, and everything a maintenance team needs in one place: work orders and preventive maintenance, inspections and the field app, plus a parts store with purchasing, compliance and certificate tracking, multi-location assets with a full lifecycle, and the KPIs that prove it’s working.
- Work orders
- Preventive maintenance
- Procedures, inspections & field app
- Parts & purchasing
- Compliance
- Assets, reports & KPIs
Good to know
How do you calculate safety stock?A simple method for spare parts is (most units used in a day × longest delivery time) minus (average units used per day × average delivery time). With 4 and 12 against 2 and 7, safety stock is 34 units.
What is the difference between safety stock and reorder point?Safety stock is the buffer you keep for slow deliveries or busy weeks. The reorder point is when to order: average daily use times delivery time, plus the safety stock.
Which parts need safety stock?Parts whose shortage stops a machine, parts with long or unreliable delivery times, and parts you use every week. Rarely used, cheap or quickly delivered parts usually need little or none.
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