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Consumers very often buy goods that have been pre-packaged. To protect consumers, regulations are used to control the quantity of product contained in packages in order to ensure that consumers get the quantity that is indicated on the package. 

NSAI Legal Metrology Inspectors carry out inspections of packaged goods, such as standard packages found on supermarket shelves. These goods are normally checked at the p[production plant/ warehouse or the importers premises to ensure that these packages contain the correct amount of product.

Traders, packers and importers have a responsibility to ensure that packaged goods comply with legal requirements and these goods may be subjected to inspection by legal metrology inspectors at any time. 

Average System

The system operates according to three rules:

  • Rule 1. The contents of the packages must not be less on average than the nominal quantity (i.e. that marked on the label).
  • Rule 2. Not more than one package in 40 may contain less than the nominal quantity by more than an amount known as the Tolerable Negative Error (TNE). This amount varies according to the quantity stated on the package.
  • Rule 3. No package is allowed to contain less than the nominal quantity by more than twice the TNE.
Norminal quantity in 
grams or mililitres
TNE a percentage of 
nominal quantity
TNE in grams
or mililitres
5 to 50 9 -
from 50 to 100 - 4.5
from 100 to 200 4.5 -
from 200 to 300 - 9
from 300 to 500 3 -
from 500 to 1000 - 15
from 1000 to 10,000 1.5 -
from 10,000 to 15,000 - 150
above 15,000 1 -

Importers Guidelines
Packers Guidelines
E-Mark on Packaged Goods
Packaged Goods Act 1980

No. The average quantity system can only be applied to packages made up out of sight of the purchaser and intended to contain a definite pre-determined quantity.

For example, standard packs of Cheddar cheese made up to a nominal quantity of 250g are covered but packs of the same cheese which are made up, weighed and marked with a variable weight (i.e. catchweights) are excluded from the average system.

Other types of exclusions from the average system are listed in the regulations. They include packages intended for export, except where the packer asks the Director of Legal Metrology, in writing, to treat packages of a specified class or description as packages to which the system applies.

Thus a packer of goods for export has freedom to use whatever system is acceptable to their customers abroad. If the packer is exporting to another state within the EEA, it is an advantage to opt to come within the system as they will then be able to obtain documentation to satisfy their customers that the packages were subject to controls similar to those applicable in the country to which the goods are being exported.