15.2. IMTS 2010 recommendations regarding units of quantity. IMTS 2010 (para. 5.5) recommends that countries collect or estimate, validate and report quantity information in the WCO standard units of quantity and in net weight on all trade transactions. Specifically, it is recommended that:
(a) Countries use the applicable WCO standard units of quantity when collecting and reporting international merchandise trade on the basis of the Harmonized System;
(b) In the case of the HS headings (subheadings) where the standard unit is other than weight, a net weight also be compiled and reported;
(c) Weight figures be reported on a net weight basis; however, if only gross weight is available, it should be recorded and used for estimation of net weight;
(d) Countries that use units of quantity other than the WCO standard units or use units of quantity different from the one recommended for the specific commodity (HS six-digit subheading) provide the conversion factors to the recommended standard units in their metadata.
15.3. WCO standard units of quantity. In 2011, WCO adopted a new Recommendation on the use of standard units of quantity to facilitate the collection, comparison and analysis of international statistics based on the HS Nomenclature 2012 Edition. The WCO standard units of quantity are:
- Weight: - kilograms (kg)
- carat (carat)
- Length: - metres (m)
- Area: - square metres (m2)
- Volume: - cubic metres (m3)
- litres (l)
- Electrical power: - 1,000 kilowatt-hours (1,000 kWh)
- Number (units): - pieces/items (u)
- pairs (2u)
- dozens (12u)
- thousands of pieces/items (1,000u)
- packs (u (jeu/pack))
15.4. WCO Recommendation. In the WCO Recommendation on the use of standard units of quantity, one of the above standard units of quantity is specified for each HS six-digit subheading. Further, it is recommended that Member administrations and Contracting Parties to the Harmonized System Convention report international trade data to the United Nations and other international organizations, in terms of standard units of quantity specified in the annex to the WCO Recommendation, employing as many as possible, but not less than 90 per cent of the HS subheadings. It is recognized that in the commercial practice of many countries the quantities of some goods might be recorded in other units of quantity, as the application of the WCO recommended quantity units is not an international legal obligation. If such non-standard units are in use, it is a good practice to provide users with the appropriate factors of conversion to net weight and, if required by users, to the appropriate WCO standard units of quantity.
15.5. Recommended quantity units by subheading, heading and HS Chapter level. For 75.8 per cent of the six-digit subheadings of HS 2012, the recommended unit is kilograms and for almost 21.3 per cent it is number of items (see table XV.1). Other recommended units are mainly used for very specific commodities. For example, “square metres” is the recommended quantity unit for, among other commodities, carpets and other textile floor coverings (HS 2012 heading 57.02); “1,000 kilowatt hours” only applies to electrical energy (HS 2012 code 2716.00); “metres” is the recommended quantity for only two headings, namely, photographic film in rolls (HS2012 heading 37.02) and cinematographic film (HS2012 heading 37.06); “pairs” is mainly used for footwear (HS2012 headings 64.01 to 64.05) and skis and ice skates and roller skates etc. (HS2012 heading 9506); and “litres” is the recommended quantity unit only for beverages, spirits and vinegar etc. (HS2012 Chapter 22). For two thirds (63 out of 96) of the HS chapters, the recommended quantity is the same for the entire chapter, and for 90 percent out of 1224 headings the recommended quantity is the same for all commodities within the heading. This indicates that the recommended quantity is the same for many commodity groupings.
15.6. Practices in the application of the supplementary units in the European Union. Supplementary units used in the European Union to measure quantity other than net mass are laid down in the Combined Nomenclature (CN) (see box XV.1).They are defined at the most detailed level, i.e., for the CN subheadings. If a supplementary unit is not given in the CN, the quantity of goods is expressed only in net mass. EU supplementary units may differ from those recommended by WCO (for example, volume for HS 271121 (Natural gas) is expressed in terajoules (gross calorific value)). The EU supplementary units are subject of annual revision of the Combined Nomenclature.
15.7. Definition of gross and net weight. Weight (in kilograms) can be measured on a net or a gross basis to meet a variety of needs. The total gross weight is defined by WCO as the weight (mass) of goods including packaging but excluding the carrier's equipment for a declaration, while net weight refers to the weight (mass) of the goods themselves without any packing. Both measures of weight have their own analytical value. For example, gross weight is more appropriate for analysis of transportation, while net weight is necessary, e.g., for the analysis of the nutritional or calorie content of imported food items.
15.8. Specific guidelines regarding the definition of net weight. IMTS 2010 (para. 5.5 (c)) recommends that weight figures be reported on a net basis, i.e., excluding all/any packaging. This also applies when the packaging is very elaborate or expensive, although one could imagine cases where the packaging itself is also a good, for example, a silver caddy containing tea, or an ornamental ceramic bowl containing sweets, or where packing materials or packing containers are clearly suitable for repetitive use, for example, certain metal drums or containers of iron or steel for compressed or liquefied gas.
 Information on net weight is useful for economic analysis, such as the calculation of unit values. To the extent that gross weights (including packaging) are also desired by a country, they should be collected directly. However, given that collection of gross weight data presents difficulties in many countries, countries may wish to obtain gross weights from net weights through sampling and estimation.
 A few exceptions may be noted: e.g., net weight does not apply to HS subheading 271600 “Electrical energy”.
 It is acknowledged that WCO standard units of quantity do not necessarily reflect industry norms for trade under certain subheadings in all countries.
 See World Customs Organization, Recommendation of the Customs Co-operation Council on the use of the standard units of quantity to facilitate the collection, comparison and analysis of international statistics based on the Harmonized System, (24 June 2011).
Available from http://www.wcoomd.org/en/about-us/legal-instruments/recommendations/~/media/WCO/Public/
 Ibid, annex, introduction, para. 4.
 Ibid., annex, para. 2. The Recommendation takes into account the amendments contained in HS2012 and revokes the previous Recommendation on the use of standard units of quantity.
 WCO Recommendation on the use of the standard units, tenth preambular para.
 The Combined Nomenclature (CN) is the classification used within the European Union for collecting and processing foreign trade data. The CN is defined on the eight-digit level, adding subdivisions to the HS. For further details on the CN, see box XIII.9.
 See WCO data set for V2.0 of the WCO Customs Data Model. Available from http://www.customs.gov.au/