Calibration Weights - Frequently Asked Questions

To improve our calibration service and to answer some typical questions about our service, please take a few minutes to read the following:

1. What standards do your weights meet?
Our calibration weights meet or exceed all necessary standards including ASTM, OIML, NIST specifications.
2 What is NIST?
NIST or the National Institute of Standards and Technology is a division of the United States Department of Commerce. They make all the regulations that manufacturers must follow to ensure industry standards. When you purchase our weights or weight sets you can be assured that they have been tested to meet their standards.
3. Are your weights certified by a NVLAP lab?
Interweigh uses only Certified Class 1 Weights to perform any Class F calibration verifications. These weights are certified by a NVLAP lab and are Traceable to a NIST Standard.

Calibration Weight Classes

What are Class 1 Weights?

Class 0, Class 1, E1, E2 - Weights are available in several classes. Class 1 weights are the most sensitive and accurate. They require clean environments and special handling. They are used to calibrate Class I/II balances, balances accurate as 0.001mg, and as a laboratory standard. Considered to be the most accurate.

Class 2 - This class is considered to have a fine accuracy and designed for Class II balances. This class would be recommended for balances that are as accurate as 1mg.

Class 3 - Recommended for analytical balances as accurate as .01g.

Class 4 - Recommended for semi-analytical balances accurate to 0.1g. These are ideal for balances in school laboratories and industrial settings.

Class 5, Class 6, and Class 7, Class F - These weights are ideal for industrial and harsh environments. They are typically used for calibrating scales used in the home or in a work production setting.

Calibration Weights


4. What is NVLAP?

NIST also runs the National Voluntary Laboratory Accreditation Program (NVLAP). This program evaluates and accredits laboratories in their respective fields and ensures they meet ISO standards.

5. What is ASTM?

The American Society of Testing and Materials or ASTM is an international organization that establishes and develops methods for testing materials. ASTM weights and weight sets are made to the tolerance, construction, finish, and magnetism set by them. ASTM requires that weights can only be made of one piece and cannot include any fillers or air to compensate for small adjustments. ASTM weights are recommended for calibrating other weights or high resolution balances.

6. What is OIML?

The International Organization of Legal Metrology (or Organization Internationale de Metrologie) or OIML is an international organization that sets guidelines for legal metrology. These guideliness cover everything from how the weights are manufactured to how they are to be used in calibration procedures.

7. Are your weights traceable to NIST?

We maintain a complete set of Primary Mass Standards directly traceable to NIST. Our weights and weight sets are provided with a detailed traceable certificate. This certificate is accredited by NIST/NVLAP, ASTM, and/or OIML depending on the type of weight, manufacturer, and class. It contains information such as type of weight, weight class, density, uncertainty, and environmental conditions at the time of calibration.

8. Do you provide a certificate of calibration or a calibration report?

Yes. This report is similar to the traceable certificate but will have a smaller uncertainty and more precise values. This has to do with the methods involved as well as the number of times the tests are repeated.

9. Do I need a certificate for my weights?

This depends upon your needs and requirements. You need to check with your governing agency, quality control department, or product literature. Usually if dealing with ISO-9000 requirements you will need some form of an NIST traceable certificate.

10. How often do I need to have my weight(s)/weight set(s) calibrated?

At least once a year.

11. How do I get my weights to you?

Download and complete a Mass Calibration Order form. Click here to download a MCO form. Arrange to deliver your weights to Interweigh Systems Inc. 51 Bentley Street, Markham, Ontario L3R 3L1 Att: Mass Calibration Laboratory. We can also offer you an efficient pick up and delivery service via our courier business partner. Please call or email us for rates.

12. How long will it take to calibrate my weights?

Once received your weights will be verified, cleaned and recalibrated (if required) within their Class tolerance; and then return shipped within 4 business days for Class F weights and within 10-15 business days for all others.

Contact us today: Toll Free: 1.800.268.3269 or by Email:

The Ownership and Management - Interweigh Systems Inc. 51 Bentley Street, Markham, Ontario, Canada, L3R 3L1
Phone: (416) 491-7001 ~ Toll Free: (800) 268-3269 ~ Fax: (905) 940-1711

Or contact us at one of our five locations: Markham, Mississauga, Woodstock, Montreal and Calgary