Guide to Buying a Calibration Weight

  • Our website offers a comprehensive, up-to-date buyers guide for Cast Iron and Stainless Steel OIML Calibrated Weights and how they must comply with OIML & Trading Standards regulations. Its important to note, there are 2 very different types of 'stamped' weights, details for which are below. We calibrate/adjust our own range of weights using Sartorius and Mettler Toldeo scales and comparators in conjunction with reference weights.

  • Trading Standards Metrology Departments are an integral part of the regulation of the UK's National Weights & Measures. We  have good relationships with local Trading Standards offices who can verify and certify our complete range of Calibrated Weights. Weights purchased from us, the manufacturer, verified and certificated by them offers you the very best lead times, price & quality.


Cast Iron 


Solid Brass


Stainless Steel 

  • Cast Iron - Firstly, this is the cheapest option and ideal for many applications. Cast Iron is very hard wearing and will give a very long service life. These weights are ideal when the handling environment is not pristine and the weights might get knocked or scratched. The best permitted OIML accuracy for cast iron weights is M1. Although this is a very accurate standard of calibration stainless steel weights can be calibrated to much finer tolreances. 


  • Brass - The maximum permitted accuracy of Brass Calibration Weights is M1. Suitable for scales with a resolution of +/- 1 grams to 0.5grams. Brass offers good corrosion resistence so its suitable for environments where moisture or mild chemicals may come into contact with the weight. Over time it will tarnish and its not as hard wearing or chemically resistent as Stainless Steel. 


  • Stainless Steel -  These weights are best suited to laboratory environments or where the weights might frequently come into contact with water, chemicals and solvents. Corrosion and stain resistent, they are extremely hard wearing but need to be handled carefully. Stainless steel high resolution calibration weights must be stored and handled with great care. Suitable for scales with a resolution of +/- 0.1grams or better. 



Trade Approved Weights & Scales


  • Firstly, if you are using an older analogue scale with internal spring type mechanism and manual adjutment then it's a Crown Stamped Trade Approved weight you will need to zero a scale that is used to weigh and then sell or buy goods on rate per gram/Kg basis. However......


  • .....Electronic Trade Approved Scales such as a Class II Jewellery Scale would require an F1 or E2 Stainless Steel Calibration weight. A Class III Electronic Trade Scale would require an M1 Calibration weight.  Class II & III scales are already calibrated to comply with Trading Standards regulations so they do not require a Trade Approved weight. It is however, best to check with your local Trading Standards Metrology Department.


  • It is legal requirement to use a scale or weight that is Trade Approved.  


  • This type of weight is calibrated with a specific positive balance which ensures the customer is getting the minimum specified amount. 


  • These weights are checked by Trading Standards and Crown Stamped. We can calibrate weights to Trade specification here at JWS with the correct positive balance.


  • No certificate is usually issued with Trade Weights but Trading Standards and JWS Weights will issue one if it is required.


  • Weights Regulations 1986 apply to Trade Weights. 




E1, E2, F1, M1, M2 and M3 'Test Weights'


  • 'Test' Weights - Used for calibrating scales, load testing lifts, cranes, lifting platforms, etc. E1 is the most accurate, then E2, F1, M1, M2 and M3 in Cast Iron.


  • E1 Test Weights - These are for calibrating scales with a 0.001mg to 0.0001mg resolution.


  • E2 Test Weights - These are for calibration scales with a 0.1mg to 0.01mg resolution. 


  • F1 Test Weights - These are for calibrating scales with a 1mg to 0.1mg resolution. 


  • M1 Test Weights - These are for calibrating scales with a 0.1g to 1 g resolution. 


  • M2 Test Weights - These are for calibrating scales with a 0.2g to 2g resolution. 


  • M3 Test Weights - These are for calibrating scales with a 0.5g to  5gram resolution. 




Shield Stamping 'Test Weights'


  • Shield Stamping Test Weights - If your business operates with ISO9001, 'Test' Weights for scale calibration can be independently verified by Trading Standards. The lead in the adjustment pocket is stamped with their official 'Shield Stamp'. A Trading Standards Certificate is always issued with a Test Weight that has been Shield Stamped. One certificate will cover a batch of weights, of different denominations but must be on the same order and for the same customer. 

  • For load testing purposes an M3 Test Weight is adequate and is unlikely to require Shield Stamping unless the weight will be audited under an ISO9001 QS, or similar. 

  • Serial numbers can be stencilled or stamped onto these weights using metal stamps so the weight is then fully traceable and linked to a certificate.




UKAS Test Weights


  • UKAS Test Weights are submitted to a UCAS approved Laboratory for testing under the requirements defined by UKAS. 

  • Each weight must be given a serial number so that it is identifiable on the UKAS Certificate. The serial number can either be stencilled on or stamped onto cast iron weights using metal stamps. For stainless steel weights the serial number can be labelled somewhere on the storage container. 

  • We also offer the Stainless Steel M1, F1 and E Class weights with the German DAkkS Certification. DaKKs is the German equivalent of UKAS and certification under DaKKs is equivalent to UKAS.



Certificates of Conformity


  • Certificates of Conformity are issued by local Trading Standards offices. Only one certificate is required for orders of multiple weights, of various denominations, on the same order and for the same customer. 

  • Customers whose quality system specifies traceability under UKAS should however purchase UKAS tested weights and a UKAS Certificate. 

  • We also issue a basic JWS Certificate of Conformity for our range of Bar Weights which confirms the calibration of the weight has been performed using comparator weights traceable to National Standards.  

Go to our FAQ Page for more help. 

James W Shenton Ltd

Tinsley Street 

Great Bridge 



Tel:  0121 557 5124


For further services and information go to:


Trading Terms & Conditions with James W Shenton Ltd 


Test Weights

Traceable to National Standards. 


Made in the

West Midlands, UK.

Certificated by Trading Standards




Copyright James W Shenton Ltd