Suppose a SKU has been assigned to the forward area; how many pallet locations should be devoted to it?

    The “minimum practical number of locations”, which we shall write as li , is determined by several factors, including the need to avoid stockout while awaiting restock.For example, if the time to restock a SKU is large or unpredictable, it might be preferable to store two pallets of that SKU in the forward-pick area. The extra pallet gives some flexibility to the timing of restock, so that when one pallet has been picked empty, the order-pickers can continue to pull product from the remaining pallet. Sometimes it is preferable to defer all restocks until the end of the pick wave (scheduled chunk of work), after which the forward area could be restocked without interfering with picking. In this case, each forward SKU would be stored in quantity sufficient to satisfy customer requests during the wave. In effect, the extra pallets allow scheduling of restocks rather than simply reacting to need. The cost is forfeiture of some of the value of the forward area, because the extra pallets take up space that could be used by other SKUs.

    Another reason to store more than one pallet of a SKU forward is to avoid congestion among the order-pickers, especially if they are picking to pallet jack or truck. By storing popular products in multiple forward locations there is less chance that a picker has to wait for  a colleague to move out of the way.

Example 7.1. Suppose that, to avoid stockout, SKU i must have at least three pallets forward if any and to avoid congestion it must occupy at least two locations. Then if the forward pick area is the ground floor of 1-deep pallet rack, holding one pallet of SKU i per location, SKU i would require at least 

which, in this case, would hold three pallets. On the other hand, if the forward pick area is 2-deep pallet flow rack, SKU i would require at least

li = max （ 3 pallets/2 pallets per location  , 2 locations）= 2 locations,

     Once a SKU has been allocated its minimum required number of pallet locations,

there is no benefit to be gained from giving it additional space — unless one has decided to store every pallet of this SKU forward, in which case both less-than-pallet and fullpallet picks are faster, and there are no internal replenishments.