Test Weights

METTLER TOLEDO's world-leading expertise in metrology extends to test weights, weight sets and calibration weights Our weight portfolio covers weights according to OIML or ASTM from fifty micrograms to five tons in all accuracy classes. Our test weights are used all over the world, not only for testing balances but also as primary standards in mass laboratories.

Our proprietary electrolytic polishing process for knob and wire weights in the upper class range eliminates microscopic protrusions in a weight’s surface. This makes the test weight far smoother when compared to weights finished with mechanical polishing. Thanks to the enhanced properties of the passive oxide film that is created on the test weight, the test weight’s long-term stability is improved.

Choose from a comprehensive selection of test weights and related calibration services. We offer weights and services of the highest quality – even for users with limited budget. Building on many years of experience and customer feedback, our weight boxes and accessories have an unmatched reputation. Profit from short recalibration times and trustworthy services. Use our global network of accredited mass laboratories for your next test-weight recalibration.

Test your balances securely, and in accordance with USP General Chapter 41 by using just two test weights to test at 5 % and 100 % of the capacity of each balance. Not only is this unique approach much faster, but it also substantially reduces test-weight purchasing and recalibration costs. CarePac^® include tweezers, gloves and other accessories for professional weight handling.

Calibrating Scale: Premium-quality weights to satisfy stringent testing requirements

Calibrating scale testing requirements have become more complex, requiring that the scales survive years of use in rough industrial environments. Ensuring scale calibration is key to extremely accurate and efficient production using a fully calibrated scale. Test weights for scales are important tools for weighing scale calibration.

If a scale is not calibrated, it can significantly cost a company financially, and even worse, it can damage its reputation. METTLER TOLEDO’s calibrating scale/test weights are perfectly designed to support testing and calibration of industrial scales. With a strong engineering focus on safe and productive testing, cast-iron weights up to 5 tons are perfect for this application, satisfying even the most stringent testing requirements. For washdown and hygienic environments, high-grade stainless-steel weights are the perfect choice for the best performance. These test weights are available in different shapes and accuracy classes to ensure proper scale calibration and scale recalibration.

Select Your Question:

1. What are calibration weights for balances?
2. What are OIML and ASTM calibration weight classes?
3. Why should I use certified calibration weights?
4. How to use a calibration weight set for routine balance testing?
5. What are the benefits of using stainless steel weights?
6. Why/how often do I need to recalibrate my test weights?
7. What are sub-milligram weights?
8. What are buoyancy artefacts?
9. Why is a silicon sphere used for specialized volume measurement?
10. What are heavy-capacity weights used for?
11. How do you calibrate a scale? What are calibrated scales? Are certified calibration weights required?
12. What are calibrated test weights used for? Are they used to calibrate weight scale systems? Do you offer test weights for scales?
13. What is the weighing scale tolerance limit of any scale? Can all scales offer precision weights?
14. What are scale weights? Are they calibration weights for scales? Must they be certified weights?
15. How do you calibrate a digital scale without weights?
16. What do you use to calibrate a scale?
17. Do you offer calibration weights?
18. Do you offer crane test weights for sale?
19. What are the differences between OIML classes?
20. Plus Tolerance
21. What is routine testing?
22. In what packaging units can I buy weights?
23. How often do you need to re-calibrate your weights?

1. What are calibration weights for balances?

Weights are predominantly needed for performance tests and routine testing of balances and scales. In metrological terminology, a distinction is made between reference weights or "mass standards" (to calibrate other weights) and certified weights. National regulations and international recommendations define the error limits of certified weights. Weights are classified into tolerance limits which are defined either by OIML or ASTM. The conventional weight value (and not the mass) is used as the nominal value of the weight. For a high level of accuracy, certified weights are calibrated and traceable back to primary standards, which are usually national standards maintained by a National Metrology Institute (NMI).

2. What are OIML and ASTM calibration weight classes?

Weight classes are separated according to the error limits that are classified either according to OIML (International Organization of Legal Metrology) or ASTM (American Society for Testing and Materials) declarations as follows.

The OIML weight

• Class E1 weights are intended to ensure traceability between national mass standards and weights of class E2 and lower (i.e. F1 and F2). Class E1 weights or weight sets shall be accompanied by a calibration certificate.
• Class E2 weights are intended for use in the initial verification of class F1 weights and for use with weighing instruments of accuracy class I. Class E2 weights or weight sets shall always be accompanied by a calibration certificate. They may be used as class E1 weights if they comply with the requirements for surface roughness and magnetic susceptibility and magnetization for class E1 weights (and their calibration certificate gives the appropriate data).
• Class F1 weights are intended for use in the initial verification of class F2 weights and for use with weighing instruments of accuracy class I and class II.
• Class F2 weights are intended for use in the initial verification of class M1 and possibly class M2 weights. They are also intended for use in important commercial transactions (e.g. precious metals and stones) on weighing instruments of accuracy class II.
• Class M1 weights are intended for use in the initial verification of class M2 weights and for use with weighing instruments of accuracy class III.
• Class M2 weights are intended for use in the initial verification of class M3 weights and for use in general commercial transactions and with weighing instruments of accuracy class III.
• Class M3 weights are intended for use with weighing instruments of accuracy class IIII.
• Classes M3 and M2-3 are lower accuracy weights of 50 kg to 5 000 kg and are intended for use with weighing instruments of accuracy class III.*

*The error in a weight used for the verification of a weighing instrument shall not exceed one third of the maximum permissible error (MPE) for an instrument. These values are listed in section 3.7.1 of OIML International Recommendation 76 Non-automatic Weighing Instruments (1992).

ASTM Weight

• ASTM Class 0: Used as primary reference standards for calibrating other reference standards and weights.
• ASTM Class 1: Can be used as a reference standard in calibrating other weights and is appropriate for calibrating high-precision analytical balances with a readability as low as 0.1 mg to 0.01 mg.
• ASTM Class 2: Appropriate for calibrating high-precision top loading balances with a readability as low as 0.01 g to 0.001 g.
• ASTM Class 3: Appropriate for calibrating balances with moderate precision with a readability as low as 0.1 g to 0.01 g.
• ASTM Class 4: For calibration of semi-analytical balances and for student use.
• NIST Class F: Primarily used to test commercial weighing devices by state and local weights-and-measures officials, device installers and service technicians.

3. Why should I use certified calibration weights?

ASTM class 0 and ultra-class as well as OIML class "E0" and E1 should be used for the highest level of precision i.e. mass standards (calibrating other weights), micro-balance testing and calibration, and critical weighing applications.
ASTM classes 1 & 2 and OIML classes E2 & F1 should be used for precision applications i.e. analytical balance testing and calibration.
ASTM classes 3 & 4 and OIML classes F1 & F2 are best suited to top-loading balance calibrations and testing and moderate precision applications (laboratory non-critical).

Note: If a balance or scale is calibrated, the weight set used and the class must be documented.

4. How to use a calibration weight set for routine balance testing?

For routine testing, specially designed CarePac sets are recommended and the nominal value should suffice for most process requirements. The tests to be carried out depend on the criticality of the weighing process. Based on a risk assessment, a GWP^® Verification provides information for routine testing frequency. It also provides a calibration schedule and maintenance plan tailored to your specific processes and risks. SOPs are available to help you determine adequate testing procedures.

5. What are the benefits of using stainless steel weights?

Stainless steel weights have long-term stability. All METTLER TOLEDO weights are made of premium stainless steel to make them corrosion resistant. Monobloc weights are specially designed for long-term stability and weights with an adjusting cavity provide the best value for the money. Electrolytic polishing ensures glossy surfaces for anti-adhesion effects.

6. Why / how often do I need to recalibrate my test weights?

Accurately calibrated test weights are the basis of accurate weighing results. The accuracy of test weights becomes less reliable over time. This is the result of normal wear and tear caused by regular use, dirt and dust. Periodic recalibration of test weights at an accredited mass-calibration laboratory is essential to ensure ongoing traceability. At our accredited mass-calibration laboratories, we clean, calibrate, and adjust each weight and then document the results in a calibration certificate. Our calibration services cover the basic reporting of conventional mass correction, uncertainty and traceability information in accordance with ISO/IEC 17025 requirements.

The frequency with which to recalibrate your test weights depends on the criticality of the weighing process. A GWP^® Verification provides not only recommendations on how to calibrate, test and maintain your weighing instrument. It advises on selecting the correct test weight and weight class and also provides recommendations on how often to recalibrate your test weights. All of this information is determined based on your specific processes and risks. 

As a risk-based service, GWP^® Verification helps to eliminate redundant or erroneous testing. Furthermore, it provides a complete set of audit-proof documentation to safeguard your full compliance with regulatory requirements.

7. What are sub-milligram weights?

Microgram weights were made available by METTLER TOLEDO in response to increasing customer demands for values below one milligram. Weights are packaged with specially designed accessory sets and handling tools to provide a complete solution for operators who go beyond traditional weighing boundaries.

These weights are also traceable and therefore have certified values which are necessary for critical applications such as those used in nanotechnology. Download the white paper on micro-weights  to learn more.

8. What are buoyancy artefacts?

Air density is usually calculated from relevant air parameters such as air temperature, pressure, humidity and CO2 concentration. An alternative method of determining air density may be applied by utilizing two specially designed buoyancy artefacts. Both artefacts are compared in vacuum and in air. By comparing the two artefacts of identical nominal weight, the large volume difference reflects the air buoyancy and therefore results in a highly accurate determination of air density. The buoyancy artefacts are mainly used for the M_one vacuum mass comparator.

9. Why is a silicon sphere used for specialized volume measurement?

Spheres are used because the volume can be determined according to the definition of volume by a length measurement. Silicon (Si) spheres have the same homogenous atomic structure as a perfect diamond without voids or dislocations, so the density is more accurate than other materials. This is why a silicon sphere with a homogenous atomic structure serves as a reference for specialized volume measurement.

10. What are heavy-capacity weights used for?

Mass comparators go up to a capacity of six tons. Industrial scales go up to several hundred tons. Heavy-capacity weights—typically those in the range of 200 kg, 500 kg, 1 t and 2 t are used for sensitivity, eccentricity, linearity and repeatability testing of these higher-capacity devices. Weights are less than 2 t due to the maximum lifting capability of machines, typically forklifts and cranes. However, these weights can be combined to reach the desired weight. Professional weights such as METTLER TOLEDO’s have lifting hooks and design features that allow them to be lifted by forklift. Barrel (round) weights are illegal as they roll and could injure a service technician.

Heavy-capacity weights must be transported in heavy-duty trucks and it is important to ensure trucks do not exceed their rated load limit due to safety and government regulations. Heavy-capacity weights are generally constructed of cast iron not stainless steel due to the cost.

11. How do you calibrate a scale? What are calibrated scales? Are certified calibration weights required?

With large stainless-steel test weights of up to 2 tons, calibration laboratories rely on the exceptional value that our test weights offer. METTLER TOLEDO offers an extensive weight portfolio for the calibrating scale that covers weights from 1 milligram to 5 tons in all accuracy classes. From grip-handle weights to cylindrical weights, each type of test weight offers its own set of benefits during scale calibration and recalibration. This ensures that the scales you use in your processes are calibrated scales. We also offer certified calibration weights to ensure regulatory compliance.

Some grip-handle weights, for example, are ideal for clean room and washdown applications, while others feature welded construction and a glass-bead-blasted, passivated surface that works for heavy-duty operation within harsh environmental conditions. To avoid manual handling operations during scale calibration and scale recalibration, METTLER TOLEDO has designed weights that offer a myriad of lifting options as well. For a calibrating scale job, workers are exposed to certain risks by handling heavy-capacity weights. Some of the design features include 360-degree access by forklifts, cranes and hoists. This helps workers avoid injury by minimizing manual handling hazards during scale recalibration or using a calibrating scale or crane test weights for sale.

12. What are calibrated test weights used for? Are they used to calibrate weight scale systems? Do you offer test weights for scales?

Calibrated test weights or scale calibration weights are used in scale calibration. This is a process that ensures scale accuracy. Test weights for scales or precision weights are used to calibrate weight scale systems of various levels of accuracy depending on the use and requirements. Certified test weights or precision weights should be used in these processes to calibrate weight scale systems. It is important to ensure the test weights are calibrated test weights and that they are accurate to provide accurate calibration results. Check out our range of scale calibration weights.

13. What is the weighing scale tolerance limit of any scale? Can all scales offer precision weights?

This is the required accuracy of the scale, and specifically the tolerance of inaccuracy allowed before it is out of tolerance and in need of a weigh scale calibration by certified calibration weights. A calibrated scale will operate at a higher level of accuracy and maintain tolerance better. For this reason, weight scale calibration with certified weights for keeping the weighing scale tolerance limit is key for accurate, calibrated scales and weigh scale calibration. Learn more about keeping your weighing scale tolerance limit in your weighing processes.

14. What are scale weights? Are they calibration weights for scales? Must they be certified weights?

Scale weights are weights for scale calibration. These weights for scale calibration may be certified weights. Generally, weights for scale calibration are certified. When calibrating scale procedures are performed, it is necessary to have calibration weights for scales. Weighing scale calibration with scale weights or test weights should be performed on a regular basis depending on use. Learn more about scale calibration weights and weigh scale calibration.

METTLER TOLEDO's world leading expertise in metrology extends to certified test weights, weight sets and weight calibration services, as well as calibration weights for scales. The weight portfolio covers scale weights according to OIML or ASTM from fifty micrograms to five tons in all accuracy classes. Our test weights are used all over the world, not only for testing balances but also as primary standards in mass laboratories. We invite you to learn more about our certified test weights and consider using them in your weighing scale calibration and weigh-scale calibration processes.

The proprietary electrolytic polishing process for knob and wire weights in the upper-class range eliminates microscopic protrusions in the weight’s surface which is far smoother compared to mechanical polishing. Thanks to the enhanced properties of the passive oxide film, long-term stability of the test weight is improved. This makes METTLER TOLEDO calibration weights for scales some of the finest in the world. Ask us about our calibration weights for scales.

15. How do you calibrate a digital scale without weights?

Theoretically, any scale needs a weight to calibrate it and assure highly accurate weighing. If high accuracy is not required, METTLER TOLEDO CalFree can be used to calibrate the scale by using the plant values of load cell and terminal to calibrate. This enables fast and easy calibration to a certain level of accuracy. Additionally, for tank scales RapidCal can be used to calibrate. This is a force calibration method that uses hydraulics to pull down on a tank to calibrate it, rather than using test weights. For a floor scale, typically weights will need to be used.

16. What do you use to calibrate a scale?

Large stainless-steel test weights of up to 2 tons can be used to calibrate scales from small bench scales to large heavy capacity floor scales. METTLER TOLEDO offers an extensive weight portfolio for calibration, covering weights from 1 milligram to 5 tons in all accuracy classes. From grip-handle weights to cylindrical weights, each type of test weight offers its own set of benefits during scale calibration and recalibration.

17. Do you offer calibration weights?

METTLER TOLEDO offers calibration weights in different masses in both OIML and ASTM standards.

18. Do you offer crane test weights for sale?

METTLER TOLEDO offers safe, stackable industrial test weights. These test weights can be moved by forklift or crane and can be used to test a crane scale or hoist scale. These crane test weights for sale are available. Contact METTLER TOLEDO for more about crane test weights for sale.

19. What are the differences between OIML classes?

The exact difference is explained in the OIML guideline, but at a basic level, E1 has the narrowest and M1 the highest tolerance limit, i.e. E1 is the most accurate.

20. What is plus tolerance of test weights?

Weights are calibrated according to OIML maximum permissible errors (+/- in mg). If the result of the calibration is in the plus range, it means that the weight is heavier than the specified nominal value, but still within the tolerance. Since most weights lose weight over time due to wear, it is more likely that this weight will take longer to fall out of tolerance (maximum permissible error). Through our production processes, most of our weights are calibrated in the plus range.

21. What is routine testing?

In short, a routine test can be compared to work which you perform yourself on your car in-between the maintenance service, like checking the oil or tire pressures. To perform a routine test on your balance, we recommend using two weights. For customers who do not know which weights are suitable for their application or balance, we are happy to advise. For this purpose, there is a so-called GWP^® Recommendation or verification software, which your METTLER TOLEDO contact can use, so that the customer then knows which weights, in terms of OIML or ASTM class and the correct mass needed for their application.

22. In what packaging units can I buy weights?

We provide the weights as single weights, in a CarePac or weight set with or without a calibration certificate.

23. How often do you need to re-calibrate your weights?

Depending on how often the weights are in use, weights should be re-calibrated every 1-2 years. METTLER TOLEDO has its own calibration laboratories around the world. Contact local representative.