Checking the weight of pre-packaged products
Have you ever had the doubt that a product weighed less than what is stated on the label? Or have you tried to weigh a product (e.g. a cosmetic, as food products can have natural weight loss) and noticed that the weight did not correspond to the manufacturer’s claim? You have not necessarily been cheated; it is likely that your scales are not accurate or, as it is often the case, that there is that small deviation, plus or minus, that is tolerated by law.
Pre-packaged products and weight tolerance
What is a pre-packaged product? A product is pre-packaged when it is contained in a package of any kind, closed in the absence of the buyer and prepared in such a way that the quantity of the product contained therein has a fixed value and cannot be altered without opening or manifestly altering the package. In the case of liquid products, the weight shall be indicated in litres, centilitres or millilitres. For products with a solid mass in kilograms or grams.
There are also specific exceptions for products sold by piece or subject to considerable losses in their volume or mass when weighed in front of the buyer. For quantities of less than 5 grams or 5 milligrams, spices and herbs are excluded. For example, vegetables pre-packaged at the supermarket counter, meat or fish in trays, fall within the category of pre-packaged but of course are subject to various factors that may vary the weight.
The current legislation for pre-packaged products is: “Law No. 690 of 25 October 1978” Implementing Directive 76/211/EEC on the preconditioning by mass or volume of certain pre-packaged products), amended by Directive 2007/45/EC.
The table of tolerances for products that can circulate throughout Europe is as follows:
Weight in grams or milligrams
- 5 to 50 (tolerance 9%)
- 100 to 200 (tolerance 4.5 g or ml)
- 200 to 300 (tolerance 4.5 %)
- 300 to 500 (tolerance 9 g or ml)
- 500 to 1000 (tolerance 3%)
- 1000 to 10,000 (tolerance 1.5%)
Why can some packages not have the weight declared on the label?
Even in the case of products that are not subject to weight loss and whose packages are prepared by high-precision automatic machines, there can be deviations, so that, as we have written above, the law allows a certain tolerance. However, how can this happen? Errors due to instrumentation, uncontrollable variables, human error. The Gauss distribution, a theory that takes us back to the high school mathematics lessons, is the one that best explains the distribution of weight in a given number of equal products. In other words, if we weigh 1,000 packages of hand cream, most of the packages will weigh the right weight or very close to the weight indicated on the label, while a small number will deviate, in excess or defect, generating what, according to that mathematical theory, is the standard deviation. The further this standard deviation is from the weight on the label, the less accurate the measurement of the product.
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