Where goods are pre-packed on the premises, you can request they be re-weighed, measured or counted in front of you. All goods must be sold in metric units, eg grams, kilograms, millilitres, litres or metres.
Generally, pre-packaged goods which are marked with their quantity must contain the amount stated on the package.
Pre-packaged goods of the same kind and stated quantity — eg 500g packs of butter — must meet the 'average quantity system' rules. These rules set out strict specifications that packers must abide by to control the quantity of pre-packed goods. Although it is possible to have a few pre-packed goods that contain slightly less than the stated amount, on average the stated quantity must be correct.
Other pre-packed goods of variable quantity, eg joints of meat, must contain at least the stated quantity. The statement could be on a label, invoice, a scale display or whatever the trader tells a customer it is.