Selection of Standard Weights for Calibration as per USP – A Practical Guide for Pharmaceutical Laboratories

Introduction

Weighing accuracy is one of the most critical aspects of pharmaceutical manufacturing and QC testing. USP <41> and <1251> provide the performance requirements for balance calibration, but selecting the right class and range of standard weights can be confusing for many labs.

This article from V-CARE IMPEX, India’s leading supplier of calibration weights, simplifies the selection of standard weights for calibration as per USP, with specific recommendations for commonly used 200 g Semi-Micro and Analytical balances.

USP Requirements in Simple Terms

USP does not mandate a specific weight class. Instead, it focuses on:

• Using a weight between 5% and 100% of the balance capacity

• Ensuring balance accuracy within ±0.10%

• Using traceable, calibrated standard weights

• Maintaining weights with acceptable uncertainty

Because USP requirements are performance-based, laboratories must choose the right weight class based on balance readability and sensitivity.

Updated Recommendations for Pharma Balances (200 g Capacity): Selection of Standard Weights for Calibration as per USP

Most pharmaceutical companies use 200 g capacity balances for both semi-micro and analytical applications. Below are USP-friendly, capacity-specific guidelines.

Semi-Micro Balance (200 g, 0.01 mg readability)

Recommended Weight Class: E2

A. Minimum Weights Required for USP Calibration

Purpose	Weight Needed	Reason
Accuracy Test	10 g (5%), 100 g, 200 g	Meets USP 5–100% capacity rule
Repeatability Test	10 mg – 5 g	For determining minimum weight
Linearity Check	20 g – 100 g	Ensures accuracy across range

B. Recommended Weight Set (Pharma Practice)

➡️ Complete E2 Calibration Weight Set (1 mg to 200 g) or

➡️ Working Set:

• Small weights: 10 mg, 20 mg, 50 mg, 100 mg, 200 mg, 500 mg

• Routine weights: 1 g, 2 g, 5 g, 10 g, 20 g, 50 g

• Calibration weights: 100 g & 200 g

Why E2 Class?

Because semi-micro balances are highly sensitive, E2 is the preferred weight class for USP compliance.

Analytical Balance (200 g, 0.1 mg readability)

Recommended Weight Class: F1

A. Minimum Weights Required for USP Calibration

Purpose	Weight Needed	Reason
Accuracy Test	10 g (5%), 100 g, 200 g	Satisfies USP requirement
Sensitivity/Intermediate Check	50 mg – 10 g	Common daily verification practice
Linearity Test	10 g – 100 g	Ensures reliable performance

B. Recommended Weight Set (Industry Standard)

➡️ Complete F1 Calibration Weight Set (1 mg to 200 g) or

➡️ Working Set:

• Small weights: 50 mg, 100 mg, 200 mg, 500 mg

• Routine weights: 1 g, 2 g, 5 g, 10 g, 20 g, 50 g

• Calibration weights: 100 g & 200 g

Why F1 Class?

Analytical balances do not require ultra-high precision. F1 provides the ideal balance between accuracy and cost-effectiveness.

Standard Weight Selection for Other Pharma Balances

Micro Balance (1 µg readability)

• Class: E1

• Range: 1 mg–20 mg

Precision Balance (1 mg or 10 mg readability)

• Class: F1 or F2

• Range: 1 g–1 kg

Top-Pan / High-Precision Balance (0.01–0.1 g readability)

• Class: F2 or M1

• Range: 100 g–5 kg

Platform Scales

• Class: M1

• Range: 10–500 kg

Quick Reference Table (Updated for 200 g Capacity)

Balance Type	Capacity	Readability	Weight Class	Recommended Weight Range
Semi-Micro Balance	200 g	0.01 mg	E2	1 mg–200 g
Analytical Balance	200 g	0.1 mg	F1	1 mg–200 g
Micro Balance	—	1 µg	E1	1–20 mg
Precision Balance	—	1–10 mg	F1/F2	1 g–1 kg
High-Precision / Top-Pan	—	0.01–0.1 g	F2/M1	100 g–5 kg
Platform Scales	—	1 g+	M1	10–500 kg

Why Correct Weight Selection Matters in Pharma

Selecting the correct weight class ensures:

• USP <41> and <1251> compliance

• Repeatable and accurate weighing

• Reduced OOS and batch failures

• Proper determination of minimum weight

• Better audit readiness

• Longer balance lifespan

V-CARE IMPEX supports pharma labs by supplying NABL-certified high-precision calibration weights across all classes.

V-CARE IMPEX: Your Partner for USP-Compliant Calibration Weights

We provide:

• E1, E2, F1, F2, M1 class weights

• Complete weight sets (1 mg to 200 g and beyond)

• NABL-traceable calibration certificates

• Customized calibration kits for pharma QC labs

• Expert guidance on weight selection and recalibration schedules

Conclusion

The selection of standard weights for calibration as per USP becomes much simpler when matched to the specific balance capacity and readability.

Since 200 g Semi-Micro and Analytical balances are the most common in pharma, this guide provides a clear, practical reference for selecting appropriate weight classes and ranges.

⚠️ Disclaimer

This article is intended for general informational purposes only. While V-CARE IMPEX strives to provide accurate and updated content, the information may not reflect the latest regulatory revisions or specific requirements of individual laboratories.

V-CARE IMPEX shall not be held liable for any decisions, actions, or interpretations arising from this article. Users should refer to official USP guidelines, internal SOPs, and accredited calibration service providers before final implementation.