Calibration weights are standardized masses used to verify and calibrate scales and balances in various settings, such as laboratories, manufacturing, and quality control. They are essential for ensuring the accuracy and precision of weighing instruments. Calibration weights come in various sizes and tolerances, and they are made from materials that resist wear and corrosion, such as stainless steel or brass.
Using calibration weights involves placing them on the scale or balance to compare the displayed weight against the known weight of the calibration weight. If there is a discrepancy, the scale can be adjusted to ensure accurate measurements in future uses. Calibration weights are typically classified according to their accuracy, with higher classes indicating lower permissible errors.
Calibrated weights and test weights are two expressions for the same thing. Calibration weights and test weights comply with OIML and ASTM guidelines and can be purchased with or without a calibration certificate.
While there are different types of weight construction, the main difference between balance calibration weights and scale calibration weights is the nominal weight value. In the laboratory, weighing instruments are often referred to as balances. For such applications, METTLER TOLEDO’s weight portfolio includes balance calibration weights from 0.05 mg (50 µg) up to 50 kg. In industry, weighing instruments are often referred to as scales. For these applications, we offer weights for scale calibration from 1 kg up to 5 tons.
If you are unsure which calibration weights you need, our free GWP® Recommendation service helps you select the right weights for your application and process accuracy requirements. For a more comprehensive assessment of your needs, our GWP® Verification service provides you with a full routine testing and calibration schedule, including the test type, test frequency, calibration weights, and weight class according to your precise needs.
Contact your local METTLER TOLEDO representative for a free GWP® Recommendation.
Read more about our GWP® Verification service here:
Weighing Devices - Verifying and Maintaining Accuracy Over Time
OIML single calibrated weights have classes E1, E2, F1, F2, and M1. ASTM single calibrated weights have classes 1 to 4.
Yes, single calibration weights can be purchased with or without a calibration certificate. However, if it is necessary for you to be able to prove traceability, you should always purchase balance calibration weights and scale calibration weights with a calibration certificate.
To test your balance or scale, only two calibrated weights are required. We recommend using one calibrated weight equivalent to the capacity of your weighing instrument and a second calibrated weight equivalent to around 5% of the capacity. You may wish to use a third weight to test your balance around a specific weight value. You can purchase our calibrated weights separately, or our CarePacs offer a cost-effective solution. Each CarePac contains two selected weights and weight handling tools appropriate to the weight value together in one convenient easy-clean plastic box. However, if you have many balances or scales with different capacities, a full set of calibrated weights may be the more cost-effective option.
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.
There are some golden rules for handling calibration weights for scales and balances that also apply to all knob, sheet and wire weights:
Monobloc calibration weights are made in one solid piece whereas a calibration weight with an adjusting cavity has a top that can be removed to reveal the cavity within the body of the weight. During the weight calibration process, minor adjustments can be made to the overall weight value by adding or removing special material. This should only be carried out by accredited calibration laboratories.
Weight Class | E1 | E2 | F1 | F2 | M1 |
Cavity | ✓ | ✓ | ✓ | ||
Monobloc | ✓ | ✓ | ✓ |
METTLER TOLEDO offer monobloc calibration weights as well as calibration weights with an adjusting cavity. However, the construction depends on the weight class as can be seen in the table above.
Weight Class | E1 | E2 | F1 | F2 | M1 |
Sheet | ✓ | ✓ | ✓ | ||
Wire | ✓ | ✓ | ✓ |
METTLER TOLEDO offers both sheet and wire milligram calibrated weights. However, the shape depends on the weight class as can be seen in the table below. In the higher weight classes, E1 and E2, only wire weights are available. This is because their smaller surface area, in comparison to sheet weights, makes them less susceptible to the effects of air buoyancy and the influences of air drafts. Hence, their higher level of accuracy.
Calibration of weights on a regular basis is essential if accuracy, repeatability, and traceability are important to you. Scale calibration weights and balance calibration weights will need to be sent to a special service provider to be calibrated against weights of a higher weight class. You may find it useful to have a second set of calibration weights so that you can continue to test the performance of your balances and scales while the other set is being calibrated.
Calibration weights are commonly made from materials such as stainless steel and brass. Stainless steel is preferred for its durability and resistance to corrosion, which helps maintain accuracy over time. The choice of material can affect the weight's density and stability, impacting measurement precision and reliability.
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.
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.
Environmental factors such as temperature, humidity, and air pressure can influence the performance of test weights. For example, changes in temperature can affect the weight's dimensions and density, while humidity can lead to moisture accumulation on the weight's surface, impacting measurement accuracy. It is important to perform calibrations in controlled environments to minimize these effects.
Traceability in calibration weights refers to the ability to link the measurements of weights to national or international standards through a documented chain of comparisons. This is important for ensuring the accuracy and reliability of measurements. Traceable weights meet quality standards and regulatory requirements, providing confidence in the calibration process and its results.