A Guide to buying Class III Scales

So you need to buy a scale...there are lots of questions, what type of scale should you buy? Does it need any special certifications for your intended use? If so, how do you make sure you can legally use it? What does Class III Approved mean? And what are Green M stickers and CE marks anyway? ...Confused? Hopefully not by the end of this guide.


What's it all about?

If you are simply weighing yourself at home to keep an eye on your weight (which is a great idea by the way) or you just need to know the weight of a product for your own reference then your don't need to worry about the legal jargon below. Although there are no legal requirements for scales intended for your own personal use, accuracy and reliability is still extremely important and we strongly recommend buying the best scale you can for your budget. There is a wide range of scales on the market, from cheap inaccurate supermarket scales to high accuracy quality weighing machines that will last a lifetime...and of course we recommend the latter!

Legal Weighing, Professional Weighing, Hospitals, Care Centres, Greengrocers, Butchers, Selling by Weight, etc.

BUT, if you are using the weight from the scale to invoice a customer (like in a butchers) or in the Medical scale world to calculate prescriptions, monitor health signs etc. then its a different story. In Hospitals for example the importance of accurate medical weighing cannot be underestimated. Stories in the press over the past few years have highlighted cases of people becoming ill after their prescriptions were calculated from non-approved and inaccurate scales, even though, by law, all scales used for professional medical use must be Class III approved.

Similarly in industry and retail, supermarkets are constantly being watched to make sure they don't over charge consumers with under weight vegetables or meat. It is illegal for anyone to charge for more than the buyer is actually getting!

Where non-Class III scales are being used it is often due to misinformed purchasing departments or people being simply unaware that the scales they are using are not suitable for their needs. It is vitally important that consumers are aware of the legal requirements that are in place to ensure weighing is regulated and accurate. This guide will aim to explain these regulations and highlight your obligations as a purchaser.

In a nutshell, in Industry and Retail, if you are buying by weight or selling by weight then the scale you use should be Class III Approved.

The NAWI Directive and Medical Scales

One of the key documents in the regulation of scales is the Non-Automatic Weighing Instruments Directive (or NAWI for short). This important document defines the legal requirements for weighing scales that are to be used in the EU. Since January 1st 2003*, the NAWI Directive has applied to all scales used for the following purpose**:

"Determination of mass in the practice of medicine for weighing patients for the purpose of monitoring, diagnosis and medical treatment."

(From this definition, scales used in, for example, slimming classes or fitness centres do not have to conform to the NAWI regulations - as long as the weighing is only for reference and is not used for any purpose mentioned above.)

*Scales purchased before this time are not affected - but may be subject to the requirements of other regulations.

What do I need to do?

Now we have determined how the NAWI Directive applies to scales, we need to look at what the NAWI Directive says we need to do as consumers. In short, if you need a Class III Approved scale, ask your scale supplier to confirm that the scale you are purchasing meets the requirements of the NAWI Directive Regulations 2000 (all Class III approved scales supplied by ScaleShop do!) and check that the scale bears the necessary symbols, which are:

  • a CE Mark (the manufacturer's declaration that their product meets the requirements of the applicable EC laws)
  • a Green M sticker (a black M on a green background - the manufacturer's declaration that the scale conforms to NAWI)
  • a 4 digit number (the identification number of one of several bodies who are authorised to test instruments and confirm that they accord with the European Directive on which the regulations are based).

What are Class III Approved Scales?

The NAWI directive defines the level of accuracy required by a weighing scale by giving it a Class. The most accurate being Class I which is used for highly accurate weighing where very little error in the result is accepted. The accuracy requirements of Class I and Class II scales are too great for most applications, so the most common accuracy class and the one that is used for trading (selling by weight - like in your local grocery) and medical weighing is Class III.

Class III Verification

Before it can be used as an approved weighing instrument, a scale must undergo a strict procedure known as a "Verification Test" (sometimes called a "Stamping"). A Verification Test puts a scale through numerous demanding procedures where it must perform to the required accuracy of its Class.

Among other procedures, the Verification Test includes "Weighing Performance" (where certified weights are placed on the scale all the way from zero to the scale's capacity - the maximum weight the scale can legally show) and "Repeatability" (where the same weight is placed on and off the scale multiple times). During these tests, in order to pass, the scale is only allowed to have errors or inaccuracies that fall within the maximum allowed errors for it's Class.

The Verification Test can only be undertaken by Approved Verifiers who have the authority to "stamp" a scale (or verify that it can be use as an approved scale). Once the scale has passed its test, the verifier marks the scale by a) placing a sticker on it with their 4 digit code b) sealing it so it cannot be tampered with and c) issuing the Declaration of Conformity which is the certificate that comes with a Class III Approved scale to show it meets all required regulations.

What scale should I buy?

Now that the legal side has been explained (and you can rest assured that all Class III scales purchased from will meet all of these requirements!), you just need to decide which scale best suits your needs. There are many different types of scale, heavy industrial platforms, light retail scales, medical scales - some with height measures and can show you your BMI or Body Mass Index - an indication of your height to weight ratio), ones where you can sit on them, and ones that can be used with wheelchairs. Please take a look through our products to see which type of scale is right for you.

Once you have decided which type of scale you need, the next step is to decide how big you will need it to be and the maximum weight you will need to put on the scale (this is known as the capacity of the scale). Most of our scales come in standard sizes and standard capacities which will cover most applications, but if you need a larger scale or a higher capacity than you see here, please contact us. We specialise in custom built weighing scales and offer a wide range of solutions to suit all requirements.

Any Questions?

If you have any questions at all please do not hesitate to contact us, we are always pleased to provide free advice and support on anything relating to weighing.