Warehouse Layout, Design, and Slotting
Warehouse layout, design, and slotting tests whether you can configure flow, space, and product placement to reduce travel and increase throughput. Expect questions on U-flow versus I-flow, slotting by cube movement, forward-reserve areas, aisle design, and cross-docking.
Core rules
- Flow patterns: U-flow shares docks and consolidates receiving and shipping; I-flow separates them and suits high-volume, one-direction product flow; L-flow suits a corner site.
- Slotting places SKUs where pick travel and replenishment cost are lowest. Rank by cube movement, not just pick frequency: cube movement = picks per period x cube per pick.
- The golden zone is the waist-to-shoulder area. Reserve it for high-velocity, small-cube items that can be replenished efficiently.
- Forward pick areas hold a small number of days of supply; reserve storage holds the rest. Size forward areas from replenishment frequency and cube, not from total inventory.
- Cross-docking works when product is already allocated, inbound and outbound flows are synchronized, and staging space is controlled.
- Space utilization must respect aisle width, fire code, rack capacity, and safe equipment clearances.
Worked example
Three SKUs: A has 400 picks per day and 0.1 cubic feet per pick; B has 100 picks and 0.5 cubic feet; C has 20 picks and 2.0 cubic feet. Cube movement: A = 40, B = 50, C = 40. B should be slotted closest, even though A has the most picks, because B moves more cube through the pick path. A and C tie on cube movement; A wins on pick frequency and B's replenishment burden must still be checked. Slotting by picks alone would wrongly put A first.
Traps that cost marks
- Slotting by unit pick count and ignoring cube, weight, or replenishment.
- Placing slow-moving items in the golden zone because they are expensive.
- Designing aisle widths from equipment catalog dimensions without turning, clearance, and safety margins.
- Sizing forward pick areas from total inventory rather than days of supply and replenishment frequency.
- Treating cross-docking as free staging; it requires synchronized inbound and outbound schedules.