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USP Chapter 41 (USP41) Weighing Requirements for Balances

Did you know that when the revision to USP Chapter 41 was released in December 2013, the title was revised from “Weights and Balances” to “Balances”? The importance of this revision indicated its focus on the major area of application and the transition from terms like "analytical balance minimum weight" and "USP minimum weight" to "repeatability" and "accuracy" to help determine the operating range of a balance.

What is the United States Pharmacopeia (USP)?

The United States Pharmacopeia (USP) is an internationally recognized, non-government organization dedicated to ensuring safe, quality medicines are available to patients worldwide. USP is grounded in extensive scientific research and the contributions of medical and pharmaceutical experts to develop industry recognized quality standards that protect public health.

What is USP Chapter 41: Balances?

USP 41 is the chapter titled “Balances” and is a mandatory requirement for ensuring the repeatability and accuracy of balances used in pharmaceutical processes. When materials must be “accurately weighed” this chapter of the standard must be followed.

What are the mandatory USP Chapter 41 requirements?

The goal of USP 41: Balances is to ensure weighing accuracy that reflects current weighing methods. The USP 41 has two mandatory critical components:

  • Repeatability
  • Accuracy


The USP 41 standard does not dictate the minimum weight that can be used, but rather how the user can determine the operating range of the balance.
The balance’s operating range is determined from the repeatability of the balance at a nominal value. This is a requirement that can be performed by the user during balance calibration. During calibration, the weight used will be the maximum weight for that balance. This maximum weight will be used to perform 10 replicate weighings to calculate the standard deviation. The standard deviation is then used in a series of calculations defined in USP 41 to establish the starting point of the balance’s operating range.


Accuracy defines the test weight that can be used to test the balance. The weight must be within 100% - 5% of the capacity of the balance, and the test weight’s tolerance must be 0.10% of the nominal value. Additionally, the measurement uncertainty must not exceed 1/3 of the test weight’s tolerance as defined by the weight class. Therefore, all test weights must have a traceable calibration report that lists the correction and measurement uncertainty values.

What is USP Chapter 1251: Weighing on an Analytical Balance?

USP 1251 is the chapter titled “Weighing on an Analytical Balance” and is a guideline for working with balances and includes information on balance environment, calibration, balance uncertainties, weighing material recommendations and safety procedures. When followed, the practices in this recommended chapter eliminate weighing process errors.

At Troemner, we are here to help you with USP 41 requirements.

Troemner recommends selecting a Cal-Pak™ calibration weight set with a more precise weight class tolerance than the values calculated following USP 41. Selecting calibration weights with a tighter weight class tolerance may lower the risk in the weighing process. Consider if the calibration weights used failed their periodic calibration, an investigation may prove the process limits were exceeded. Choosing a Cal-Pak with a more precise weight class tolerance allows drift of the calibration weights between calibration cycles.
If your process limits were exceeded, you may face a recall of product due to this out of tolerance condition. Weights with a tighter weight class tolerance will reduce risk of an out of tolerance circumstance occurring.
Troemner Cal-Paks are the ideal weight sets to meet the requirements of USP 41. Cal-Pak weight sets contain high quality, precision weights that can be used with all balance manufacturers’ makes and models. Sets with (3) weights are supplied with the balance manufacturers’ recommended calibration weight, 10% of the calibration weight, and the repeatability test weight as determined by the balance’s readability and expected standard deviation under normal conditions. Cal-Pak sets that contain (2) high quality, precision weights are supplied with the recommended calibration weight and the repeatability test weight. Based on your mass measurement assurance program select the weight set that meets the USP 41 requirements and has the accuracy class needed to reduce risk.
Troemner Cal-Pak components are linked using a unique serial number. You can trace your individual weights to the appropriate ISO/IEC 17025 Accredited Calibration Certificate and master carrying case. The precision weights in your Cal-Pak are traceable to the international kg standard through an exacting series of traceable measurements that provide an accurate value for each weight with an uncertainty that exceeds the requirements of USP.

View our full line of Cal-Paks available in Troemner UltraClass and ASTM Class 1 at:

Still not sure, contact Troemner and we can help you select the Cal-Pak weight set you need in your application and compliance with USP 41.

*USP no longer refers to minimum sample weight nor related terms such as scale minimum weight, USP 41 minimum weight, USP 1251 minimum weight, USP 41 minimum weight calculation.

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