Par levels (minimum and maximum stock on hand) are how hospitals, hotels, restaurants, and parts rooms decide when to reorder. Most online par-level calculators use max-usage × lead time. This one also lets you size the buffer for consumption variance, which is the difference between a par level that works on a busy Tuesday and one that works on a long weekend.
Par level (short for "periodic allocation replacement" or, in hospitality, "par stock") is the simplest replenishment policy in use. You set a maximum (when you stop ordering) and a minimum (when you start ordering). Stockroom staff fill the bins up to max when they hit min.
This works well for:
This calculator sizes both the min and max with a variance buffer. The variance buffer is the addition that online calculators usually skip: it accounts for the fact that consumption on a holiday weekend is very different from consumption on a Tuesday.
MAX (par) = (avg daily usage × lead time in days × review period in days) + safety stock
MIN = avg daily usage × lead time in days (i.e., enough to cover until next order arrives)
Safety stock = Z × std dev of usage during review period + lead time
Mark bin locations so staff can see current stock and the MIN/MAX lines. When stock falls to MIN, place an order for MAX − MIN units. If you have a small fixed-order-cost supplier, round the order quantity up to a case pack.
Re-evaluate quarterly. If usage patterns change, the par levels drift out of date and either overstock (max too high) or stockout (min too low) result.