A recent visit to a small facility reminded me that many warehouse operations do not have a location numbering system to identify specific storage and pick locations. The day I visited that warehouse, much of the staff spent a lot of time searching for merchandise because the key members who knew where the stock was were out sick. Relying on people’s memories of where merchandise is located works only as long as the same people come to work every day.
There is a point at which the number of locations or the number of items in the warehouse grows too large for human memory to manage effectively. Million square-foot warehouses must have numbering systems to enable workers to create a mental map of the storage areas. These numbering systems are not unlike the street names and addresses we use to navigate through a city or town. While we all agree that navigating through cities like New York, Boston, or San Francisco would be very difficult without an address system, thousands of warehouse operators attempt to run their operations that way.
The interesting part of this situation for me is when we begin to discuss location numbering (or addressing) with warehouse managers, I discover how difficult it can appear to develop a numbering system and get it installed.
There are many different location-numbering systems, and they are limited only by the range of logic patterns our creative minds can develop. There is no singular right way to create a location numbering system, but some practices work better than others. Still, each of these systems works, and if you do not have one, you must take the initiative to create and install one.
What follows here is a set of proven design guidelines/logic that we have used for location numbering in many facilities, suggesting first steps to consider as you begin to change your processes to use location numbers in your picking, stocking, and inventory management.
First, you should base your location numbering on simple and consistent logic. The logic must be easy for a new warehouse employee to learn and for seasoned employees to use when rushed. Following this rule, consider basing your storage location numbering system on the systems city planners use outside the warehouse to identify street and house addresses in a typical city.
There are three fundamental constructs to consider when developing the numbering logic:
⦁ I believe the location numbering system should not include alphabetic characters. Some people like to see location addresses include ABCs instead of 123s, and perhaps using the first part of the alphabet can work, but it probably doesn’t work as well beyond E, F, or G. If you feel strongly about using alphabetic characters, I suggest using alphabetic characters for elements of the location with no more than five or six options; for example, the levels in rack or shelving, or areas of a building, but not the aisles.
⦁ Operationally, never place more than one SKU in a location at one time.
⦁ Be as specific as possible, identifying each of the elements of each logical storage location; e.g., aisle, section or bay (between uprights in rack or shelving), shelf or level (starting at the floor level and ascending), and position on the level from left to right (on pallet rack could be two or three pallet positions).
The following recommendations focus on how you should think of the end, the outcome that you want to accomplish, with the numbering system. All of these are elements to think about when developing your numbering schemes.
⦁ Each aisle should have an aisle number.
⦁ Consider using a separate sequence of aisle numbers for each logical work area in the warehouse, e.g., repack, pallet rack, floor stack, etc.
⦁ In racked areas, assign numbers to aisles instead of rack or shelving rows. This design supports cross-aisle picking. Cross-aisle picking increases picking productivity by reducing the total travel distance. The picker selects all the material required in that aisle as part of a single trip through the aisle.
⦁ If your computer programmer finds it difficult to sequence picking documents using the odd-even section location number elements, or where a conveyor installed down the center of an aisle, you can assign addresses to rack rows instead of aisles. The Pick Sequence number function in many WMS packages often overcomes this obstacle.
Generally, assign numbers to aisles ascending from 01, beginning at one side of the building and continuing toward the other. This method supports spatial orientation, so it is easy to remember that the higher numbers are toward one end of the building and the lower aisle numbers are toward the other end.
Plan for growth and let the aisle numbers grow in whatever direction the building can expand. If you have room for more than nine aisles, then plan for a two-digit aisle number. In many cases, a three-digit aisle number makes sense. We have seen more than one warehouse operation constrained in its ability to expand by a two-digit aisle number.
⦁ Select the conventional entry end of the aisles (typically nearest to the receiving dock side of the building), and assign numbers to rack sections beginning with the number 01 to “N” with numbers ascending.
⦁ Place odd-numbered sections on the left side of the aisle and even-numbered sections on the right side as you are facing the back of the building.
⦁ A section is the area between the uprights. Some use the term “bay” to describe the same space. For example, 01-01-X-X
⦁ Assign an address from 1 to “N” to each level within each rack or shelving section.
⦁ Start from the floor as level 1 and go upward in the level count.
⦁ Each level would be a shelf or pair of beams. For example, 01-01-1-X.
⦁ Within each shelving or rack-section level, assign numbers to each position, ascending from 1 to “N,” from left to right as you face the section.
⦁ Separate each location from the next with a divider, bin box, or a painted or tape-marked line on the shelf deck and lip to help keep material in its assigned location.
⦁ In pallet rack, typically there would be two positions on each level, numbered 1 and 2. For example; Location 01-01-1-1 would be for the pallet in the left side of the first level of the first bay on the left of the first aisle.
Special use locations:
⦁ In rack used for the hand stack of small amounts of cases, the location numbers on a shelf usually range from four to eight locations. Most racking systems are eight feet between upright posts, and hand stacks less than a foot wide are hard to manage.
⦁ In repack shelving or carton flow rack, location numbers again usually do not exceed eight locations.
⦁ Some operators choose to use alphabetic characters to indicate position.
⦁ To accommodate small items in drawers, we have used two digits to describe the locations using a 9 X 9 grid locator; e.g., row and column. Again, some operators will deploy alphabetic character logic, mimicking the way Excel spreadsheets use columns and rows.
⦁ In bulk floor storage locations, assign one section number to each pallet row facing the aisle, odd numbers on the left and even numbers on the right.
Once you create guidelines that make sense, use a plan drawing of your layout to verify that it works. We actually write the numbers on the layout and use it to explain it to others. Include all of your staff, particularly pickers and stock people who typically enter the storage area from the receiving dock and want to find a particular location easily. If the workers can understand your numbering system and imagine that they can find their way around the warehouse with those numbers, you are well on your way to an effective location numbering system.
Once you have the plan defined on paper, and the entire team supports the change, it is time to affix address labels to the racks.
If you drive through your town, you notice street signs at the end of each of the streets, and building numbers on each of the buildings. The town or city installs the street signs, so there is usually a degree of consistency in the street signage (but not always). But the address numbers are left to the owner of the building to execute, which can sometimes make finding an address difficult.
How many times have you missed an address in busy traffic because you could not see the building number clearly? How often have you missed a street because you could not find the street sign? The same thing happens in warehouses where the managers do not think carefully about the signage and labels used to number the warehouse.
Several companies specialize in location labeling solutions. Some will even print the numbers on the stock for you. You can buy your own stock, and with the help of your IT department you can print your own labels. The advent of new label stocks, laser printers, and software has made the process of printing their own labels more appealing to many warehouse operators. The option of printing your own labels allows the operator to replace labels damaged from equipment contact, or to replace rack beams for the same reason. It also allows for replacement if the rack levels change with the addition or subtraction of beams, or for decking of former pallet locations.
Consider the environment of the warehouse when selecting the label stock. Freezer and cooler applications will require a different kind of adhesive and paper stock than labels used in an ambient warehouse.
Some recommend using yellow rather than white stock for labels because black characters on yellow paper seem to read more clearly in medium-light areas at the end of the day. Consider the lighting in the warehouse, and the shadows, when selecting the stock. With color laser printers, many consider using different colors of printing. We recommend not using anything other than black on white or black on yellow. Colors wash out in some kinds of lighting, and some color differences are lost on colorblind people.
Consider using end-of-aisle markers that extend into the cross aisles of the warehouse, much like the street signs that mark cross streets. This allows lift truck operators to keep their eyes in the direction of travel as they navigate down the cross aisles.
Don Benson, also known as The Warehouse Coach, is a systems thinker, bringing ideas, people and organizations together to achieve their desired outcomes with Warehouse Management Systems for over 35 years. You can reach him at www.wmssupport.com.