LOGLogistics & transportationStop 9 of 10
Warehousing & throughput
How a warehouse works from dock to dock, and how slotting, picking methods and layout get more orders out of the same building.
Read atChange any time
A warehouse does five things, in order:
- Receiving: unload trucks, check what arrived against the advance shipping notice, record it.
- Putaway: move goods to a storage location (a bin) chosen by rules.
- Storage: hold stock, counted regularly so records stay accurate.
- Picking: collect the items for each order. This is usually the biggest labour cost, and much of it is walking.
- Packing and shipping: pack, label, load the right truck in the right order.
Most throughput gains come from cutting travel and touches:
- Slotting: put the fastest movers in the easiest, closest locations near the dispatch area, and slow movers further back. A velocity-based ABC on order lines tells you which is which.
- Picking method: single-order picking is simple but walks the most. Batch picking collects several orders in one walk; zone picking gives each picker a zone; wave picking releases orders in timed groups to match carrier departure times.
- Layout and flow: a clear one-way flow from receiving to shipping, with no crossing paths.
A WMS (warehouse management system) tracks every bin and quant, chooses putaway and picking locations, directs workers through handheld scanners, and records each move. Typical measures are lines picked per hour, order accuracy, dock-to-stock time and cost per order.
Automation, from conveyors and sorters to shuttles and robots, makes sense when volumes are high and steady, labour is scarce or expensive, or accuracy requirements are very high.
Words to use
- Slotting
- Assigning items to storage locations based on how often and how much they are picked.
- Wave picking
- Releasing orders in timed groups, often to match truck departure times.
- WMS
- Warehouse management system: software that directs and records every warehouse movement.
Where the time goes
In a manual picking operation, a large share of a picker’s time is spent walking between locations; the rest goes on searching, picking, scanning and paperwork. Reducing travel is therefore the biggest single lever.
A picker manages 100 order lines an hour, and travel takes half of the time.
- Moving the fastest movers into the locations nearest the packing area cuts travel by 30%.
- Time per line falls to 0.5 + 0.5 × 0.7 = 0.85 of what it was.
- Productivity rises to 100 / 0.85 ≈ 118 lines an hour, an 18% gain with no new equipment.
Slotting rules
- Velocity: rank items by how often they are picked (order lines, not units) and put the top movers closest to dispatch and at waist-to-shoulder height (the “golden zone”).
- Size and weight: heavy items low, light items high, large items where handling equipment can reach them.
- Affinity: items often ordered together placed near each other.
- Review regularly: seasonal items and new products change the ranking.
Batching and waves
- Batch picking: one picker collects several orders in one walk, sorting into separate totes. Travel per order falls sharply, but sorting is needed.
- Zone picking: each picker stays in a zone and orders pass between zones, which suits large warehouses.
- Wave picking: orders are released in timed groups so picking finishes in time for each truck’s departure.
Planning capacity
Two capacities matter:
- Storage: pallet and bin positions needed for average and peak stock. Warehouses run poorly when nearly full, because putaway slows and stock gets placed in temporary locations, so plan for headroom at peak.
- Throughput: lines, cases or pallets a day that labour, docks and equipment can handle. Peak days, not average days, set staffing and dock schedules.
Storage systems: density against access
| System | Density | Access | Suits |
|---|---|---|---|
| Selective pallet racking | Medium | Every pallet directly | Many SKUs, mixed movers |
| Drive-in or push-back racking | High | Last in, first out by lane | Few SKUs with many pallets each |
| Very narrow aisle racking | High | Every pallet, with special trucks | Large ranges in expensive space |
| Shelving and flow racks | High for cases and items | Fast hand picking | Case and each picking |
| Automated storage and retrieval | Very high | Machine-controlled | High volume, high labour cost, steady flows |
When automation pays
Conveyors, sorters, shuttles, goods-to-person systems and robots raise throughput and accuracy and reduce labour, but they cost a lot and are hard to change. The business case is strongest when volumes are high and fairly steady, labour is scarce or expensive, accuracy requirements are very high, or space is costly. Flexible options, such as mobile robots that bring shelves to pickers, reduce the risk when the future is uncertain. Automating a messy process only makes the mess faster, so fix the process first.
E-commerce fulfilment
Online orders are many and small: often one or two items each. That changes the warehouse:
- Each picking instead of cases and pallets.
- Batch picking with put walls, where items picked for many orders are sorted into order cubbies.
- Packing stations choosing box sizes to avoid shipping air.
- Cut-off times driven by carrier departures, with waves planned backwards from them.
- Returns processing as a regular flow, not an exception.
Routing pickers through aisles
Even with good slotting, the path through the aisles matters. Simple rules such as the S-shape (walk through every aisle that contains a pick) or the largest gap method (enter and leave an aisle from the same end when the picks are near it), and optimal routing in layouts with cross aisles, cut travel further. Roodbergen and de Koster (2001) compared such methods for warehouses with multiple cross aisles.
Measures that matter
Lines picked per labour hour, order accuracy, dock-to-stock time (how fast receipts become available for orders), order cycle time, inventory record accuracy from cycle counts, storage utilization, and cost per order or per unit shipped.
Interview kit
Practise it out loud
Answer each question yourself before opening the model answer.
A warehouse runs receiving, putaway, storage, picking, and packing and shipping, and picking usually dominates labour, mostly through walking. To raise throughput I’d slot fast movers near dispatch based on pick frequency, choose batch, zone or wave picking to fit the order profile, keep a one-way flow, and use a WMS to direct work. I’d measure lines per hour, accuracy, dock-to-stock time and cost per order, and consider automation where volume and labour economics justify it.
How would you increase a warehouse's picking productivity without new equipment?
Re-slot by velocity so fast movers sit near dispatch, switch from single-order to batch or zone picking, optimize pick paths, release work in waves aligned to carrier cut-offs, and fix stock-record accuracy so pickers don’t hunt for missing items.
What does dock-to-stock time measure, and why does it matter?
It’s the time from a truck arriving to the goods being available in a pickable location. Long dock-to-stock time means stock exists physically but can’t be sold or shipped, which causes stockouts and extra safety stock.
Connected stops
Where this idea feeds in, or gets its inputs from.
Sources and further reading
- Bartholdi, J. J. & Hackman, S. T. Warehouse & Distribution Science. Georgia Institute of Technology. Free online.
- Frazelle, E. H. World-Class Warehousing and Material Handling. McGraw-Hill.
- Bartholdi, J. J., & Hackman, S. T. Warehouse & Distribution Science. Georgia Institute of Technology.
- Roodbergen, K. J., & de Koster, R. (2001). Routing methods for warehouses with multiple cross aisles. International Journal of Production Research, 39(9), 1865–1883.