Maintenance Spares Optimizer
Optimize spare parts inventory using MTBF and Lead Time demand. Enter values for instant results with step-by-step formulas.
Formula
ROP = (LeadTime × UsageRate) + (Z × √LeadTimeUsage)
Reorder Point (ROP) ensures you have enough parts to survive the Lead Time. It combines Expected Demand (LeadTime × Usage) plus a Safety Buffer (Z × StdDev) to account for randomness in failure rates.
Worked Examples
Example 1: Critical Motor
Problem:MTBF 1000h, Lead Time 30 days, Usage 24h/day
Solution:High demand during long lead time requires significant buffer.
Result:Spares: 3 units
Example 2: Consumable Filter
Problem:MTBF 500h, Lead Time 2 days, Usage 8h/day
Solution:Short lead time minimizes risk.
Result:Spares: 1 unit
Example 3: Rare Failure
Problem:MTBF 50,000h, Lead Time 14 days
Solution:Demand is near zero. Keep 1 just in case (Insurance spare).
Result:Spares: 1 unit
Frequently Asked Questions
What about 'Insurance Spares'?
Parts that rarely break (MTBF > 10 years) but are critical. Standard formulas say 0 stock, but you keep 1 for insurance against catastrophic risk.
Why not just buy tons of spares?
Capital is tied up in inventory (holding cost). Parts degrade (rust, seals dry out). Efficient MRO balances risk vs cost.