When should you reorder a spare part?
Use lead-time demand, a safety buffer and open orders to make a purchasing decision.
Define demand and lead time in matching units
Measure how much usable stock is normally consumed and how long replenishment really takes. If demand is measured per working day, express lead time the same way. Include receiving and inspection time when the part is not available immediately on arrival.
Calculate a starting reorder point
A practical starting rule is average demand during lead time plus safety stock. If average use is 3 units per day, lead time is 8 days and the buffer is 10 units, the reorder point is 34 units. This is an example, not a recommendation for every item.
Use inventory position, not the shelf count alone
Before ordering, consider usable stock plus confirmed incoming quantities minus outstanding commitments. Check whether a purchase order is still expected and whether reserved stock is truly available. Otherwise a low shelf balance can trigger a duplicate purchase.
Choose the buffer for the uncertainty
Demand and supplier lead time vary. Review how often the item runs out, the consequences of downtime, expiry risk and the cost of holding stock. Intermittent demand and critical spares may need a different policy from regular consumables. A simple average does not describe every risk.
Review thresholds after the facts change
Revisit the rule when equipment, demand or suppliers change. Dastyar’s inventory and project records help track quantities and movements. Use the recorded history in a purchasing review; do not present a manually set minimum as an automated forecast.
Further reading: Association for Supply Chain Management: inventory management.