Maintenance · Updated 4 October 2026
Spare parts reorder levels and stock coverage
Separate stock physically available today from inventory position and incoming purchase orders.
Agree the item and the demand basis
Use one part code and one unit of issue. Derive average daily usage from a representative period, recording whether calendar or working days were used. Demand for a critical spare can be intermittent, so a small historical average does not automatically justify holding no spare.
Separate three stock quantities
On-hand stock is physically received stock. Inventory position adds confirmed incoming orders and subtracts reserved or backordered quantities. Available coverage uses physical stock after commitments, divided by usage. Incoming orders may reduce a purchase gap, but they cannot support an immediate repair before arrival.
Calculate the reorder point
With daily usage of 2 units, lead time of 10 days and safety stock of 5 units, the reorder point is 25 units. On-hand stock of 20, incoming stock of 5 and commitments of 2 give an inventory position of 23. The reorder threshold has therefore been reached even though a purchase order is already open.
Choose a target and review supplier constraints
For an additional 5-day coverage period, target stock is 2 multiplied by 15, plus 5: 35 units. The target gap from an inventory position of 23 is 12 units. This is a planning suggestion rather than an economic order quantity. Check minimum order quantities, packs, shelf life, substitution, delivery dates and equipment criticality before ordering. Review lead time after late deliveries and distinguish obsolete parts from essential standby spares.