One of the underpinnings of materials handling system design is the unit load principle – handle as large a load as possible to reduce the total number of moves. Pallet load handling has been synonymous with this principle for years.

But since the debut of just-in-time, we have pulled back from the unit-load-is-always-a-pallet-load concept. We have pulled back not because the concept is bad but because our needs have changed. For many products, a full pallet represents several weeks of supply. And good inventory management dictates that we get better at handling not just large quantities but smaller quantities too.

Now we've moved on to other units such as the half pallet. That is often a better unit for production, replenishment and filling orders. Even if a production run needs multiple half-pallets, the smaller load provides a better balance between inventory control and minimal case handling.

Other handling units deserve similar scrutiny. For instance, how many units should be packed in a case? Presumably, it should be a quantity that is, or could be, a common ordering increment. The beverage industry is an example.

Traditionally, beverages were offered in 6-packs and full cases of 24. But, the full case was just a little more than consumers could comfortably handle. How many case handling moves did they eliminate when they introduced the intermediate sized 12-pack?

Years ago, we developed an approach toward unit load design for manufacturing processes with a capacity that matched the number of pieces that were loaded in a staging rack or fixture for a machine cycle. This eliminated partial loads and the extra handling that went with them.

The same principle could be applied to totes and containers that stage materials. We should choose unit load sizes that match their capacities.

For products that require multiple pallets a day, double stacking them for transport and storage saves both handling moves and space.

When inventories of a single product reach the 100-plus pallet level, the unit load principle moves up the scale. They might be left on trailers and pallets transferred at the dock to fill outbound orders. The key is to put only one stock keeping unit in the trailer, and bring it to the dock only once. The warehouse gets significantly smaller. And, the handling distance for the fastest moving products is reduced to a simple crossdock move.

In a project involving the movement of automobiles through several steps of cleaning and re-conditioning with storage in-between, the handling unit might be determined by the number of drivers that fit in a shuttle van. Consequently, storage lanes for the cars should be in those increments.

Similarly, good engineering principles and analysis apply to the selection of the capacity of a shuttle bus serving remote rental car and parking lots at the airport. How fast do the customers arrive, and how long is it reasonable to ask them to wait?

As you can see, unit load theory is not limited to the classic pallet dimensions. There are many different definitions and configurations. The question is; what are the right unit loads for your operation?