When should I reorder, and how many units?
Reorder when inventory position reaches the reorder point, then round the gap to your chosen coverage target up to a whole supplier case pack. Count committed and already-on-order units before acting.
Method
Safety stock uses maximum-use minus average-use during lead time. Reorder point adds average lead-time demand. Order quantity fills the chosen coverage target and rounds up to a case pack.
Important limitation
This simple method is not a statistical forecast. Promotions, intermittent demand, perishability, minimum orders, cash limits and stale stock counts require separate judgement.