As you roll out your SAP system across multiple companies and countries, however, needs like conversion from metric to US/British Imperial measure arise that necessitate a more detailed analysis of the UoM configuration. Lack of attention to the conversion factor for a UoM or other local settings can, at least, irritate or confuse users. At worst, miscalculated documents can be sent to customers or foreign customs officials, resulting in blocked shipments or expensive disputes.

Another major area of concern is the conversion of quantities from one UoM to another and the problems unfavorable rounding differences can cause. This happens most often with conversion between two US or British Imperial UoMs (e.g., pounds to ounces). In extreme cases, this type of rounding error can bring your warehouse operations to a halt.

What follows are the 11 most common pitfalls to watch out for when you are working with UoMs and quantity fields. I’ll also give you details to help you fix and avoid the problems.

1. Incorrect Selection of Base UoM for a Material

Consider a company that produces fiber optic cable and chooses kilometer (KM) as the base UoM. In SAP all quantity fields are maintained internally to three decimal places, so the smallest quantity of fiber optic cable that can be delivered to a customer is 0.001 KM, which is 1 meter (M). So what happens when a customer wants 10 centimeters (CM) of fiber optic cable? This would be 0.0001 KM, which cannot be represented in SAP if KM is chosen as the base unit.

The base UoM defined in the material master is the UoM, in which the material is managed by SAP (Figure 1). The SAP system converts all the quantities you enter in other UoMs (e.g., alternative UoMs) to the base UoM. In older versions of SAP, this field was referred to as the stock-keeping unit (SKU). For Inventory Management (MM-IM), the base UoM is the same as the SKU.

Figure 1

Base UoM is defined in the material master. Use the Additional data button to enter alternate UoMs.

Careful selection of the base UoM helps minimize rounding errors in stock quantities. For dimensionless UoMs, choose the smallest UoM, such as each (EA), instead of the larger case (CSE). For other UoMs, choose a base unit carefully. The actual choice depends on the nature of the material. If your base UoM is too small, then large quantities of the material cause an overflow in the quantity fields. If the base UoM is too large, accuracy is lost, since all quantities are stored at a maximum of three-decimal-point accuracy. For example, for length it is often safer to choose M over millimeters (MM) or KM. See SAP note 362932 for more information about rounding with UoMs. Once business transactions have started using the material the base UoM cannot be changed in most cases, as explained in SAP note 138767.

The wrong base UoM can also result in problems with batch splits in deliveries. For example, say the UoM in the sales order is different from the base UoM in the material master and the conversion factor cannot be described accurately using three decimal places (e.g., 1 pack [PK] = 7 EA). In some situations, the total of the delivery batches does not add up exactly to the sales order amount. This results in the sales order not being marked as fully delivered. See SAP notes 107219, 135821, and 139966 for more details.

2. Failure to Configure Alternate UoMs for a Material

Converting quantities in one UoM to another UoM and adding up total quantities in multiple UoMs are frequently required for logistics activities. For standard SAP conversions, all UoMs must belong to the same dimensions for regular conversion (e.g., length is converted from inches to M but length in inches is not converted to weight in kilograms).

Alternate UoMs used as conversion factors cannot be set up centrally for dimensionless UoMs or between UoMs of different dimensions. You can configure this on a material-by-material basis only using the alternate UoM functionality. For more details, see SAP note 523496.

Rounding errors in Warehouse Management (WM) can result in blocked shipping, as small variances between picking and goods issue amounts prevent goods issues from being posted. Consider the following example: An item has base UoM EA and alternate UoM PK, where 1 PK = 7 EA. This becomes 1 EA = 0.143 PK. Since accuracy for quantities goes only to three decimal places, when this is multiplied by 7 it results in 7 EA = 1.001 PK in WM. This is different from the 1.00 PK expected in MM-IM goods issue. The reason for this error is the chained conversion Alternate UoM>Base UoM>Alternate UoM, which results in rounding differences.

Prior to SAP R/3 Release 2.1, this was a major problem. SAP changed WM functionality to store quantities internally in the entered UoM and not to automatically convert to the base UoM. If you make any manual quantity entries in the WM transaction screens, however, even overwriting a quantity with the same number, a conversion takes place. The system behavior of quantity conversion only upon request is implemented in the entire transfer order processing, so you can avoid superfluous quantity conversions. See SAP note 5555 for more details.

A follow-on problem encountered in WM is almost-empty storage bins, when 0.001 of a material is left in the bin due to rounding errors. This results in the bin not being released for reuse. You can correct this by making a physical inventory adjustment or, in more serious cases, applying SAP notes. See SAP notes 125636 and 162816 for more details.

Click on the Additional data button, shown in Figure 1, to enter or display alternate UoMs, in transaction MM01, MM02, or MM03 (Figure 2).

Figure 2

For an individual material, you can configure alternate UoMs to allow conversion between any types of UoMs

Alternate UoMs are commonly used at order entry when purchasing or selling materials. You can define UoMs other than the base UoM in the material master specifically for sales, purchasing, and production, as shown in Table 1. In the case of a base UoM with dimension, you can use any UoM with the same dimension. For example, you can order a material with base UoM of M in KM or CM without defining alternate UoMs.

One advantage alternate UoMs have for defining central conversion factors is that they allow material-specific translation. In the example of the motor oil in Figure 2, 1 case = 24 quarts, but for orange juice you may want 1 case = 12 quarts. One disadvantage is that the conversion factor needs to be set up material-by-material, which can be time-consuming and can easily result in errors given the number of material master records most SAP installations have.

If you are defining a common alternate UoM relationship for many materials, you can use Define Units of Measure Groups in the IMG, SAP Customizing>Logistics - General>Material master>Setting for key fields>Define units of measure groups to set up the relationship once for use in many material master records.

3. Overlooking Costing Lot Size

When configuring materials for production processes and the associated product costing, the Costing Lot Size field (Figure 3) is often overlooked. On a bill of material (BOM), you might have fractions of a UoM you normally only see as whole units (e.g., pallets [PAL]). Rounding issues related to this UoM can result in incorrect costing.

Figure 3

Costing Lot Size in the Costing 1 view of the material

Consider the following example. You have a BOM for producing 1 EA in a box (i.e., lamps in boxes). Usually eight lamps go on one pallet, so you add 0.125 PAL per 1 EA lamps. For planning purposes you can use fractions of PAL. When posting, the number is rounded up to the next PAL. When you produce one lamp, the production/process order contains 1 PAL instead of 0.125 PAL. When costing such a BOM, make sure you use the Costing Lot Size on the material master Costing 1 view, since costing also rounds up fractions of PAL. If a lamp is USD 5 and the pallet is USD 20, one lamp on one pallet would cost USD 25, whereas if you have a costing lot size of eight or a multiple thereof, a lamp would cost (8*USD 5 + USD 20)/8 = USD 7.50.

4. Incorrect Conversion Factors

Consider the following situation: A customer orders five miles of fiber optic cable. The quantity is entered as five miles, which is the sales UoM, in the sales order. However, at delivery you find it has been converted to five meters, the base UoM. This is due to errors in the conversion factors. To prevent this, make sure you review the SAP standard conversion factors. In the R/3 4.7 IDES system used in these images, for example, the US mile was configured incorrectly to be equal to one meter. For a list of key tables used by SAP for UoM configuration, see Table 2

Conversion Factors

A key factor in dimension configuration is the definition of the UoM known as the System Internationale (SI) UoM, for each dimension. This is the basic unit employed in all conversions between different UoMs with the same dimension (Figure 4). The SI setting is made by SAP and cannot be changed. Do not delete the SI UoM for a dimension under any circumstances, as conversion between UoMs with that dimension will be impossible.

Figure 4

For the dimension length M (meter) is defined as the SI unit in transaction CUNI

In transaction CUNI (IMG path SAP Customizing>General Settings>Check units of measure), you can define the conversion factor between the UoM and the SI UoM. In the case of metric measures, these are simple multiples of 10, which do not introduce any complications.

Conversion Testing

To test UoM conversions when displaying the UoM in transaction CUNI, use the convert icon in the toolbar, and enter the conversion you want to test in the popup (Figure 5). If you do not have access to transaction CUNI, use ABAP RSBZME10 instead to test conversions. The test popup can give the misleading impression quantities can be calculated to 15 DPs — in actuality, quantity values are stored with three DPs.

Figure 5

Example of rounding error: conversion should be 3 pounds = 48 ounces, using transaction CUNI

In an SAP system with several different SAP instances, the conversion settings must be the same for all UoMs used across all SAP instances. This is of particular relevance when using New Dimension products like APO and SRM, which reside on their own server but communicate with the main R/3 system. Refer to SAP notes 492979 and 595742.

5. Rounding Errors During Conversion of US/Imperial UoMs

When working with metric measures, conversion factors are usually very simple (e.g., 1 KM = 1000 M, 1 L = 1000 ML) with no concerns about rounding. With US/Imperial UoMs, however, the relationships are not as straightforward and errors can result.

As the conversion factors between US/Imperial and metric UoMs are usually approximate fractions, rounding differences nearly always occur when you move between the two systems and are even worse when converting between two US/Imperial UoMs (e.g., pounds to ounces). The system often converts them via an intermediate conversion to the metric/SI UoM (Figure 6), adding rounding errors to what should be an exact conversion (Figures 5 and 6).

Figure 6

Example of rounding error: conversion should be 3 pounds = 48 ounces, using ABAP RSBZME10

To add to the confusion, not all US/Imperial UoMs are the same. For example, a US gallon is 3.785 liters, while a UK gallon is 4.545 liters.

If conversion factors are maintained centrally in customized UoMs, the conversion is always relative to the respective SI unit. If the US/Imperial UoM in question has a small size relative to the main UoM (e.g., 1 inch = 0.0254 meters), it can be difficult to maintain the conversion factors accurately in the configuration.

One solution proposed by SAP is to define all non-metric UoMs as dimensionless. This allows you to define the conversion factors with maximum accuracy in the material master. The disadvantage is that you have to make sure organizationally that all materials with the same UoMs use the same conversion factors in the material master. Also, any combinations you have forgotten to define cannot be converted. This solution helps primarily with conversion from one US/Imperial measure to another and not with conversion to metric units. See SAP notes 20307, 23771, and 362932 for more information.

6. UoM with Incorrect Dimension

UoM configuration is done via transaction CUNI. The initial screen of the CUNI transaction lets you configure dimensions, International Organization for Standardization (ISO) UoM codes, and SAP UoM codes. Select the dimension and click the Units of measurement button to see the overview screen in (Figure 7). When creating a new UoM, you must choose a dimension to which it belongs (Figure 8).

Figure 7

UoM display for dimension Length

Figure 8

Sample set of dimensions in an SAP system; the specific list depends on your SAP release

A dimension is a set of categories that group together similar UoMs and assist in quantity conversions. There are seven base dimensions, to which all other dimensions can be traced back: length, weight, time, electrical current, temperature, molecular mass, and brightness. Quantity conversions can only occur between UoMs with the same dimension. Figure 8 shows a sample list of dimensions in SAP. Using alternate UoMs (see section 2), you can define cross-dimension conversions on a material-by-material basis.

I often see UoMs created with the default setting (no dimensions) when the UoM clearly belongs to a defined dimension. For UoMs with no dimension, common UoM conversions (e.g., gallons to liters) cannot be performed using central configuration, but need to be defined on a material-by-material basis. This can lead to a large overhead for maintaining material master records. It also results in error messages such as V1 297 Quantity could not be converted from GA to L.

The reason this occurs is that users do not understand what a dimension is and accept the default value (no dimensions). For example, assigning the UoM GL for gallon to (no dimensions) is incorrect, because GL has the dimension of volume.

As previously discussed, there is a scenario in which you may choose to deliberately configure US/Imperial UoMs as (no dimension). Be sure to make this decision actively.

If a UoM has been configured with an incorrect dimension, you can delete the UoM configuration and recreate it with the correct dimension. Be careful when doing this, as there is no validation on existing use of the UoM. Recreate the UoM as quickly as possible after deleting it, or you may have materials with an invalid base UoM that cannot be processed. Use report ZRBZMEFIND in SAP note 637003 to search for UoM use prior to deleting or changing a UoM. When you do change a UoM dimension, you must test that the change does not cause any problems with logistics and manufacturing transactions.

7. Use of US ANSI UoM Codes Instead of ISO UoM Codes

When communicating electronically with external parties (e.g., vendors and customers) through electronic data interchange (EDI) and other means, a global standard for UoMs must be used so that all systems interpret the UoM code consistently. This is the function of the ISO codes. The ISO UoM code is assigned to the SAP UoM code via transaction CUNI (Figure 9).

Figure 9

UoM configuration details for Meter (M)

Many modules in SAP are designed to work with external data files using ISO UoMs. With Supplier Relationship Management - Catalog Content Management (SRM-CCM), for example, you must upload an XML or CSV format file for the SRM-CCM catalog. In this file, the UoM field needs to be the ISO UoM code. To ensure the upload works correctly, you must check the following: your input file uses ISO UoM, in transaction CUNI the ISO code exists, the ISO code is assigned to an SAP UoM code, and the ISO primary code check box is set correctly. A user logging on to the SRM system sees the SAP UoM code displayed.

One problem area is that in the US, the American National Standards Institute (ANSI) UoM codes are used for EDI and other electronic communication. The ANSI codes don’t always match the ISO codes (e.g., ANSI GA vs. ISO GAL for gallon). In some cases, you may find the ISO code field is actually populated with the ANSI code. If you use multiple EDI systems or standards and one calls for the ANSI code and the other for the ISO code, this can lead to mis-conversion of UoM codes.

You have several methods to get around this:

• Change the ISO field to contain the ANSI UoM.
  
  
• Create a second SAP UoM with the ANSI UoM in the ISO field.
  
  
• Have a custom translation table to convert the ANSI UoM to the ISO UoM prior to selection of the SAP UoM.
  
  
• Add a UoM translation table to any EDI middleware you may use.

The SAP R/3 and ECC systems determine which SAP-internal UoM is to be converted into which ISO code. One ISO code can be assigned to several SAP units for outbound messages. For inbound messages, you must also determine which ISO code is to be converted into which SAP unit. Use the check box Primary code for this. A common example is the ISO code PCE for piece, which corresponds with SAP codes AU (activity unit), PER (persons) and PC (pieces). The SAP code PC is chosen as the primary code for translation of inbound EDI messages (Table 3). See www.unece.org/etrades/codesindex.htm for more information on ISO UoM codes.

8. Incorrrect Number of Decimal Places

When calculating quantities or displaying quantities on documents such as a commercial invoice, you may be under a legal or contractual obligation to calculate or display the quantities using a specific number of decimal places. It is also common practice in certain industries to use a specific number of decimal places. If you fail to configure UoMs to yield the correct amount of decimal places, at the very least, your output might look a little odd. At worst, a foreign customs official may hold up your shipment.

To be sure you get the correct output format for quantity fields:

1. Configure the DPs for the UoM correctly in transaction CUNI.
   
   
2. Make sure the quantity field has a related UoM reference field.
   
   
3. Make sure the output ABAP or SAPscript makes use of the reference UoM field for the quantity.

All quantity data in SAP is stored internally as numbers with three decimal places regardless of the number of decimal places when displayed (Table 4). If no UoM reference is supplied, SAP uses the default of three decimal places for display. However, the majority of UoMs are configured for display with no decimals.

In UoM configuration, there are two fields for the decimal places with distinct purposes. Both are configured via transaction CUNI, as you saw in Figure 9.

The display decimal places field is used for controlling the number of decimal places for screen and list output of related quantities. EA, for example, is usually shown with no decimal places, while milliliters (ML) is usually output with three decimal places.

The decimal place rounding field is used to determine the level of accuracy for internal calculations using the UoM (e.g., internal rounding during the creation of a production order). However, the rounding decimal place is not considered by every transaction, so SAP recommends that you set the rounding decimal places of UoMs to three (like the number of the decimal places of the quantity fields), especially when you are using metric and non-metric units of measure simultaneously, which is the case where rounding differences are most likely. Additional information is available in SAP notes 77525 and 362932. If you are working with a UoM in which quantities must always be calculated to the nearest whole units, set the rounding decimal place to zero.

Even if a UoM is configured to have rounding to zero decimal places when values are entered (e.g., during goods receipt for a PO), the decimal places are not rounded off when converting the quantity in the entry UoM into the base UoM of the material, to help maintain the value as accurately as possible in the base UoM. See SAP note 77525 for more information.

9. Lack of a UoM Reference Field

When a quantity field is output using SAPscript or ABAP to get the correct formatting, the system expects a UoM reference field. If it does not exist, the quantity may be output in the wrong format. This can be particularly important if legislation or an industry standard specifies the number of decimal places to be used when printing quantities. Table 4 shows how quantities are displayed with and without reference fields.

Whenever a quantity field is defined in the data structure, a corresponding UoM reference field needs to be defined and linked to the quantity field. This is because a quantity is meaningless unless you know the units in which it is expressed. In all tables defined by SAP, a UoM reference is maintained so that the context for the quantity is maintained. When you create your own custom tables for quantities, you must link them to a reference UoM field. Use transaction SE11 or SE12 to display tables containing quantity fields, such as EKPO, VBAP, or AFKO (Figure 10 and Figure 11).

Figure 10

SE11 display of a quantity and UoM field for table EKPO. Double-click on quantity field MENGE to see detail.

Figure 11

UoM reference field for a quantity field. This popup is displayed after double clicking on the previous screen.

When viewing data in SE16, SE16N, or SE17 in the row overview screen, the values are always displayed to three decimal places regardless of UoM (Figure 12). In the row detail screen, the value could be in three decimal places or the correct number of decimal places, depending on how the reference field for the quantity field was defined.

Figure 12

Quantity data in SE16 and SE17 overview is always displayed to three decimal places regardless of the UoM

10. Custom Reporting Errors

Custom reporting is often used for documents such as commercial invoices when an SAP standard SAPscript is modified for a company-specific format. When extracting data in custom reports, make sure programmers use a UoM reference field. I often come across problems with quantity reporting when this has not been done. Here is some sample ABAP code using a UoM reference field for a write statement: WRITE EKPO-MENGE USING UNIT EKPO-MEINS. To see how quantity values are displayed with and without a UoM reference field, see Table 2. You can check for the lack of a UoM reference using the extended syntax check in the ABAP editor, accessible through transaction SE38 or directly with transaction SLIN.

You do not need to have custom rules in your ABAP programs, hard-coded logic, or printing with special formats as to get the correct output of quantity fields. Using the UoM reference, your SAP system looks up the correct number of decimal places automatically and formats the quantity correctly.

When working with UoM conversions, SAP provides several standard function modules that do all the hard work for you, so you can avoid creating new code to look up conversion routines (Table 5). If you need to test function UNIT_CONVERSION_SIMPLE using SM37, you can run into problems. Use ABAP RSBZME10 instead.

If you use the ALV grid for reporting, include the UoM reference field in your data table and cross-reference the quantity field to the UoM field in the field catalog. The ALV grid uses this information to display values correctly and to subtotal columns with values in multiple UoM correctly (Figure 13). Showing a total of 82,030.88 available stock is meaningless as it is the sum of L + M2 + PC. Instead, ALV subtotals by each UoM.

Figure 13

Subtotals by UoM are formed automatically by ALV if a UoM reference field is provided

When working with SAPscript, the correct number of decimal places is displayed if the quantity field used has the UoM reference field defined. If your SAPscript is based on an SAP standard SAPscript and displays data using one of the standard SAPscript output structures, such as VBDPA or VBDPR, make sure you populate the UoM reference field (e.g., UoM field VBDPR-VRKME for quantity field VBDPR-FKIMG). 

11. Internal Storage Format vs. External Display Format

When a UoM is displayed to a user, it is translated to its language-dependent code. Internally, the UoM may be stored in a different code. This can cause problems when dealing with raw codes (e.g., loading data via a BAPI, preparing a material master load using ABAP RMMMM, or working with custom ABAPs).

For example, the UoM EA is commonly used for “each.” However, your SAP system stores this internally as ST, short for the German word for each, which is Stück. See Figure 14 for codes in different languages. This is the SE16 display of table T006A. This is why a list of UoMs called up by F4 help may appear to be in a random order, as it is sorted by the internal German language codes. With newer installations, SAP makes the internal code the English language code instead of the German, but this applies to new implementations only and would still be an issue if your main operating language were not English. The internal UoM code is displayed at the top of the UoM configuration screen in transaction CUNI. See SAP note 619937 for more details.

Figure 14

The user sees the language dependent UoM code but internally it is always stored with the same code

When working with custom ABAPs, use the following function modules to convert between SAP internal and external language dependant codes: CONVERSION_ EXIT_CUNIT_INPUT and CONVERSION_EXIT_CUNIT_OUTPUT.

Rohana Gunawardena

Rohana Gunawardena heads the SAP practice division at Exium Inc. Exium is a leading business and technology consulting firm that enables companies to achieve their strategic business goals. Exium specializes in delivering superior IT solutions using ERP systems, with a special focus on SAP products. Rohana has been working with SAP since 1992. During his career he has assisted multiple clients on detailed system correction projects, such as correcting inventory balances, controlling area reorganizations, retrospectively activating group currency, and optimizing inter-company accounting transactions. He has spoken at many SAP conferences and has published more than 20 articles in Financials Expert, SCM Expert, and SAPtips on various aspects of SAP. His presentations have focused on Financials module selection, the order-to-cash process, global rollouts, business segment reporting, cross-module integration, and the financial impact of SCM transactions. Rohana is widely acknowledged as a leading SAP expert. Rohana is a Fellow of the Institute of Chartered Accountants in England & Wales. Previously Rohana has worked with the consulting practices of Accenture, Deloitte, and PwC.

Rohana will be presenting at the upcoming SAPinsider Financials 2018 conference October 16-18 in Prague. For information on the event, click here.

You may contact the author at Rohana@Exium.com .

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