Once a commercial airliner lands and taxis to the gate, the pressure is on to get it ready for the next flight. Teams of specialists — cleaning crews, baggage handlers, fueling agents and more — work in concert to meet the next scheduled departure time. What does that have to do with warehouse wave picking? Both are built on a principle known as short interval scheduling (SIS), intended to maximize productivity and minimize inactivity by bundling tasks into a short window of time. True, 737s are not warehouses, and there are some fundamental considerations when determining whether wave picking is right for your warehouse.

What Is Wave Picking (or Cluster Picking)?

Wave picking, also known as cluster picking, is one of several order picking systems used in warehouses to improve efficiency. It involves releasing specific orders to the floor for fulfillment, based on a common factor such as shipping date, like items, warehouse zone, etc. Rather than scheduling a number of pickers per shift and then hoping that orders flow accordingly, wave picking helps teams to meet specific commitments, such as filling a set number of orders per shift or meeting a shipping deadline.

To do so, wave picking focuses on when orders are picked. Management aligns short picking intervals, or waves, that correspond with other warehouse variables, such as the transportation plan or departure schedule. The result is that orders are grouped and then picked, but only at certain times of day. Teams gain efficiency primarily by reducing (or eliminating) picker idle time. In other words, a wave might not be scheduled until all orders up to a certain deadline have come in, so pickers don’t have to spend time waiting for instruction.

Wave Picking vs. Zone Picking

Wave picking contrasts with another popular picking methodology, zone picking, which is defined by where the items are picked. But the two approaches are not mutually exclusive — some warehouses use both together. Depending on the size of the warehouse and its product mix, zones may be set up in various ways. The choices include organizing by:

  • Product type (non-perishables in one zone and fresh produce in another)
  • Risk factors (controlled narcotics in a secure zone)
  • Packing considerations (hazardous materials in one zone)
  • Sales volume (fastest sellers in one zone or zones and slowest sellers in another)

However zones are configured, pickers are assigned to one zone and only pick SKUs from that zone. This reduces worker travel time and congestion.

Key Takeaways

  • Wave picking can improve order picking efficiency by scheduling waves according to shipping schedule, carrier and other factors.
  • Wave picking doesn’t describe a single, defined process. There are several variations of wave picking, and it is often combined with other picking methodologies.
  • Advantages include timely shipping, fewer bottlenecks and less travel time, but it can be hard to process urgent or last-minute orders.
  • Effective wave picking relies on complex data analysis that is best done by a warehouse management system (WMS).

Wave Picking Explained

Establishing wave picking as a methodology helps keep workers moving at an efficient pace, ensuring that there’s a set plan. Staff collect multiple orders in specific inventory zones based on their item grouping during specific times of the day. Each wave lasts from one to four hours, breaking up shifts into manageable pieces. Shorter waves can help managers identify scheduling issues in the same day, meaning waves can be adjusted as the day goes on, if needed. This agility is a hallmark of SIS.

Without a defined methodology, order picking can become a highly inefficient process with a lot of down time. Pickers commonly spend time waiting for clear instructions, and warehouse traffic and poor planning can waste time as well. For example, a picker might need to wait for another picker who is blocking product locations with a forklift. Wave picking aims to cut idle time by focusing pickers on specific orders within a finite timeframe — a form of short interval scheduling.

Wave duration is usually determined by how many orders are being picked.

How Does Wave Picking Work?

Although the concept is straightforward, executing wave picking can be complicated because it requires a collaborative effort between multiple roles involved in the order fulfillment process, including receiving, shipping, freight companies and others. Because of this, wave picking is most effective when seen as a three-step process:

  • Pre-wave picking is the work of scheduling the waves according to specific variables. As a business processes orders, they must be logically grouped and scheduled. If they’re grouped by shipping time, for example, picking must have enough lead time to pick the orders and get them packed before the shipping partner’s scheduled departure time. This planning is much easier with the help of a warehouse management system (WMS) that can factor in all necessary variables to create an optimal picking schedule; done manually, it’s laborious and time-consuming.

  • Performing wave picking is the act of picking. It’s made more efficient with technology like hand-held mobile scanners that provide digital pick lists and direct pickers to product locations, instead of paper pick slips. These technologies can be linked to a WMS and chart optimal pick routes while tracking each step of the picking process. Using a hand-held picking device, wave picking typically works like this:

    1. A picker receives the pick list for 4-12 orders per wave.
    2. The picker uses a multi-tote cart to keep the orders separate.
    3. Pickers are sent to each storage location in sequence, and the mobile device tells the picker the SKU and quantity to pick. Pickers pull the designated product and scan its barcode to confirm the pick.
    4. Pickers place the product in its appropriate tote and scan the tote’s barcode to confirm. Pickers might also enter the quantity on the mobile device.
    5. Pickers are then directed to the next pick and the process repeats until all orders are complete.
  • Post-wave picking occurs after the items are picked. Often, orders are kept separate as they’re picked; mobile scanners and discrete totes or cartons can make this easy. But if orders are not separated, the product must be organized for sorting and packed for shipping afterward. Scheduling waves must allow time for the added sorting and packing step if necessary. Finally, orders are loaded and shipped.

infographic wave picking

How Are Waves Grouped?

How a company groups waves will depend on a variety of factors and can change from business to business or even from one day to another. This agility is a primary benefit of wave picking. Here are some ways waves might be grouped:

  • Like products. The most common way to wave pick is by selecting items that are of like kind, typically grouped in a shared space in the warehouse.

  • Shipping schedules. Many warehouses ship products using different delivery schedules, such as ground shipping, express delivery or next-day delivery — all of which may have different pickup times. Grouping waves based on shipping schedule can ensure orders are ready on time so carriers can stay on schedule and customers can receive orders on time.

  • Carriers. Different carriers have different pickup times, pricing and shipping guidelines. Warehouses that rely on multiple carriers may find that grouping all orders for a specific carrier saves time and money.

  • Replenishment picking. In a large or high-volume warehouse, it can make sense to free up valuable floor space by storing quantities of fast-selling SKUs off the floor or even off-site. When that’s done, those SKUs must be replenished — typically in their own wave — before other waves are scheduled. To prevent worker downtime, it’s useful to schedule picking waves after all SKUs have been replenished.

  • Shift changes and available workforce. Waves can be grouped to take full advantage of peak staffing, or to ensure that picking is complete before it’s disrupted by a shift change. Businesses should avoid shift changes in the middle of a picking cycle. If workers are interrupted and replacement staff must pick up where the previous shift left off, it can increase errors.

  • Product locations and similarities. Business can plan waves to pick all products in the same location, which can be particularly useful when combined with zone picking. For example, waves may be planned around similar products, such as bulky and heavy items or hazardous materials.

  • Warehouse priorities. Warehouse priorities vary depending on business needs, which change from time to time. For example, a warehouse might prioritize orders from the largest customer, or orders that have a lot of perishable products. Waves can be scheduled to tackle orders with utmost priority.

Note that none of the above options need to be all or nothing. They can be combined — maybe the wave considers priority orders and shift changes. And grouping variables can change day to day or can shift as the day progresses. No matter what, it’s important to always consider the most logical way to group waves at any given time.

Wave Picking Methods

As with other picking methodologies, there are variations: fixed wave picking and dynamic wave picking.

  • In fixed wave picking, all orders are held for packing until workers have picked all the items to fulfill all individual orders in the wave.
  • In dynamic wave picking, individual orders are sent to be packed as they are completed.

Key Differences

There are pros and cons to both approaches. Fixed wave picking makes it easier to schedule packing and shipping staff because it’s generally easier to anticipate when the wave will be complete. However, more staff may be required because all orders will then need to be assembled for picking.

Dynamic wave picking eliminates the added final step because orders are sent to packing and shipping as soon as they’re completed. This means the packing team may get by with fewer people. However, order flow may be less predictable, creating a potential for bottlenecks in the packing process.

Advantages of Wave Picking

Wave picking has become a popular methodology because it offers several advantages over traditional single order picking. Consider these plusses:

  • On-time shipping: By analyzing orders, resources and shipping schedules, wave picking makes it possible to build in the necessary lead time to pick and complete orders before shipping cut-off times.

  • Fewer bottlenecks: In single order picking, there is always the risk that too many people, too much equipment or both will end up in the same aisle at the same time. Wave picking can direct those same people and/or the same equipment to the aisle at different times, resulting in less congestion and greater productivity.

  • Faster picking: Integrating multiple variables when planning a wave makes it possible to have pickers pull higher quantities of the same SKU or to pick several SKUs in the same location. It’s also possible to plan the most efficient route through the warehouse. Both steps slash pickers’ travel time, which makes it possible to pick more in less time.

  • Increased accuracy: Once orders are picked and go to sorting, the sorting and packing team can double-check SKU count and ensure all orders are accurately fulfilled.

  • Improved tracking: A set schedule makes it easier to estimate picker progress throughout a wave, especially when handheld scanning devices are linked to a WMS. This provides managers a real-time overview of how much progress has been made and what tasks remain.

  • Good for high-value items or fresh goods: With wave picking, these items can be picked just-in-time right before shipment. This translates to less idle time, meaning less chance for high value items to be broken or stolen, and less time for perishable items to lose freshness.

Disadvantages of Wave Picking

Despite the advantages of wave picking, no order picking method is perfect. Here are some potential downsides to wave picking:

  • Possible downtime: Although eliminating downtime is a primary goal of wave picking, downtime can still occur if waves aren’t well-planned or if labor and resources are unequally deployed. For example, pickers may be slowed if they have more to pick than the pickers behind them, who may be forced to wait for the bottleneck to subside.

  • Urgent orders may be delayed: Wave picking relies on strict schedules, so it can be hard to account for emergency orders or high priority orders that come in at the last minute when a wave has already begun. If customer satisfaction is the No. 1 priority, the only way to process these new orders is to disrupt the current workflow. Neither disrupting the wave nor delaying the urgent order is an appealing option, but it is a choice management must prepare to make.

  • Can add an extra step: When orders aren’t picked directly into a shipping carton, they must be sent to sorting and packing to be correctly separated and prepared for shipping. This adds an extra step to the order fulfillment process, potentially adding more time and more room for error.

  • Multiple pickers can cause confusion: Because wave picking may require more employees, that can create more traffic and confusion in the warehouse without an effective WMS.

Five Tips to Optimize a Wave Picking Strategy

Much of the value of a wave picking strategy lies in how well each wave is planned and executed. Here are some tips that can help optimize the wave picking process:

  1. Choose an effective WMS. There are so many variables in wave picking — type of product, product location, staffing, warehouse flow, shipping considerations and so on — that humans cannot quickly and effectively distill them all to devise a plan, especially on the fly. Wave picking demands a strong WMS that can handle complex data analysis to derive the most efficient way to batch waves and pick orders.

  2. Determine delivery commitment. Setting expectations for when customers will receive their orders is a key business practice. Whether orders are sent out for same-day delivery, next-day delivery or standard ground, the wave-picking strategy must determine how those orders can be picked and processed in time to meet shipping deadlines.

  3. Consider delivery zones. If a substantial proportion of orders are all going to the same area (such as office supplies going to midtown Manhattan), it may pay to plan waves around those orders to maximize shipping efficiency.

  4. Consider cart handling strategies. What equipment do pickers need to be the most efficient? Small items can be grabbed by hand and transported within a tote on a cart, whereas large, heavy items may require forklifts or similar equipment. And if a forklift is required, staff must be trained to use it.

  5. Determine the optimal picking strategy. Reviewing all the above factors can help devise optimal waves that include the most logical picking strategy. For example, if a large, urgent order with heavy items must be picked, schedule the wave such that someone with a forklift license is available. It’s also important to remember that wave picking is not ideal in all situations, and warehouse operations must be flexible. If the warehouse is experiencing a light season, it may not be necessary to create concise coordinated schedules and single order picking or batch picking may work just fine. A WMS can help managers pick the most efficient picking strategy.

How Does a Warehouse Management System (WMS) Help?

Planning an effective wave picking strategy requires keen data analysis that accounts for numerous variables, making a warehouse management system invaluable. For example, a WMS can plan waves based on different factors like:

  • Delivery times. Waves may be planned based on when a product is promised to the customer. Products planned for ground delivery to the other side of the country would be picked at a different time than products marked for same-day delivery, for example.

  • Delivery address. Waves may be planned to pull products with the same or similar destination, such as the same zip code. Scheduling waves based on delivery address increases shipping efficiencies that save carriers time and fueling costs.

  • Shipment number. A shipment number is used to help identify a shipment, for example with a bill of lading. One shipment might include 10 crates of products, and each crate may be labeled with a distinct shipping number. A WMS can easily plan waves based on orders that must be lumped together.

  • Shipment number, shipment start loading time and shipment end loading time. Shipment numbers may also be used in a more sophisticated structure that incorporates the cut-off time for either when the shipment must start loading or when the loading must be complete. The WMS can then schedule backward by grouping orders that have the same (or similar) cut-off times.

When calculating any of these approaches, the WMS will consider delivery and transportation schedules, labor schedules, the location of each product and other variables. To do so more effectively, a WMS can connect to an enterprise resource planning (ERP) system, which can compile data from all of a business’s key functions in real time, such as order management from incoming orders to shipping management to customer service.

Many warehouses stand to benefit from wave picking thanks to its concise, clear way of scheduling short picking intervals that correspond with other key warehouse fulfillment processes, like shipping. To get the most out of the wave picking strategy, it’s important to have a WMS that can automatically analyze order data, shipping data, staffing data and warehouse organization to devise the most logical waves and picking sequences.

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Wave Picking FAQs

What is wave picking in a warehouse?

Wave picking is a commonly used order picking system. Picking is scheduled to occur within specific intervals of time, or waves, to better correspond with other important warehouse processes, such as shipping. For example, a warehouse might schedule a wave that focuses on getting a high-priority order from its largest customer out the door in time to meet the carrier’s deadline for next-day shipping.

What is the wave picking process?

The wave picking process can be broken down into three steps:

  1. Pre-wave picking, in which waves are established and scheduled.
  2. Performing wave picking, in which items are picked to fulfill customer orders.
  3. Post-wave picking, in which items are sorted and packed for shipping.

What is one drawback of wave picking?

One drawback of wave picking is that it does not leave room for last-minute urgent orders or emergency order changes. Wave picking relies on following strict schedules to meet certain demands or goals. When emergency, last-minute orders crop up, warehouse managers must decide between interrupting the scheduled wave or delaying the urgent order.