NABL Requirements for Calibration of Weights and Balances – Practical Guide for Laboratories

Setting up a calibration laboratory and preparing for NABL accreditation involves understanding key requirements related to standard weights, weighing balances, calibration methods, and documentation practices. This guide simplifies the NABL requirements for calibration of weights and balances, making it easy for laboratories, QA/QC teams, and business owners to follow.

Prepared by V-CARE IMPEX, one of India’s leading manufacturers of E1, E2, F1, F2 and M1 class standard weights, this blog covers all essential requirements in a clear and practical format.

Why NABL Accreditation Matters for Calibration Labs

NABL accreditation is crucial because it:

• Establishes technical competence of the lab

• Ensures ISO/IEC 17025 compliance

• Enhances customer trust

• Makes calibration certificates legally valid

• Is required in pharma, chemical, food, testing, R&D and manufacturing industries

• Helps labs win major industrial, government and corporate contracts

Understanding NABL requirements helps labs prepare properly from the beginning.

What NABL Checks When Evaluating a Calibration Lab

NABL focuses on 5 major areas:

✔ 1. Standard Weights (Correct class & range)

✔ 2. Weighing balances (Master instruments)

✔ 3. Environmental monitoring tools

✔ 4. Calibration procedures & uncertainty budgets

✔ 5. Traceability, documentation & staff competence

If these are correct, NABL accreditation becomes straightforward.

Standard Weight Requirements as per NABL Requirements for Calibration of Weights and Balances

NABL requires labs to use standard weights of the correct OIML class depending on the readability of the balance.

Here is the simplest and clearest breakdown:

1. Micro Balance (0.1–1 µg Readability)

• Weight Class Required: E1

• Range Needed: 1 mg – 100 mg fractional set

2. Semi-Micro Balance (0.01 mg Readability)

• Weight Class Required: E2 (preferred) or F1

• Range Needed: 1 mg – 200 g

3. Analytical Balance (0.1 mg Readability)

• Weight Class Required: F1

• Range Needed: 1 mg – 200 g or 500 g

4. Precision Balance (1 mg – 10 mg Readability)

• Weight Class Required: F1 or F2

• Range Needed: 1 g – 1 kg or 2 kg

5. Bench Scales (0.1 g – 1 g Readability)

• Weight Class Required: F2 or M1

• Range Needed: 1 kg – 20 kg

NABL Requirements for High-Capacity Platform Scale Calibration

There is significant confusion regarding NABL-required weights for 3T, 5T, 10T or higher-capacity platform scales.

The truth is:

❌ You do NOT need 3T, 5T or 10T of weights.

❌ You do NOT need 150–200 pieces of weights.

❌ You do NOT need to stack full capacity on the platform.

✔ NABL accepts practical, safe, scientific calibration methods.

✔ You typically need only 20–40 pieces of 20 kg weights.

India's leading NABL labs use this approach.

NABL-Accepted Calibration Methods for High-Capacity Scales

These methods are widely used across India and fully acceptable to NABL.

1. Substitution Method (Most Practical for 3T–60T)

You use:

• 20 kg M1 standard weights

• Customer’s material (bags, drums, pallets) to substitute large loads

Process:

1. Load 200–400 kg using certified weights

2. Record the reading

3. Replace weights with equivalent customer material

4. Repeat cycles until full load is simulated

This is the most efficient & accepted method.

2. Cyclic (Build-Up) Method

Load small amounts like 200–300 kg → record → unload → repeat.

Benefits:

• Checks linearity

• Reduces strain on platform

• Requires minimal weights

3. Distributed Loading (5-Point Corner Test)

Used when platform area is limited.

Test positions:

• Center

• Front left

• Front right

• Rear left

• Rear right

Ensures the scale reads correctly across the entire platform.

4. Client Material Method

Used in:

• Warehouses

• Factories

• Logistics

• Packaging units

Customer’s goods (bags, drums, cartons) are used as part of the total load. You verify accuracy using your 20 kg weights.

How Many Weights You Should Buy (Simple Recommendation)

NABL Scope	Recommended Weights	Quantity
3T Platform Scale	20 kg M1 class	20–25 pcs
5T Platform Scale	20 kg M1 class	25–30 pcs
10T Platform Scale	20 kg M1 class	30–40 pcs
10T–60T Weighbridge	20 kg M1 class	40–50 pcs

This satisfies NABL requirements without unnecessary expense.

Environmental Instruments Required by NABL

NABL requires monitoring of:

• Temperature

• Humidity

• Barometric Pressure

These are essential for air buoyancy correction and accurate calibration.

Labs must use NABL-traceable:

✔ Hygrometer

✔ Thermometer

✔ Barometer

✔ Data logger (recommended)

Documentation Required to Meet NABL Requirements

Every laboratory must maintain:

• Calibration SOPs

• Uncertainty budgets

• Master instrument list

• NABL traceable certificates of weights

• Environmental monitoring logs

• Internal audit records

• Management review records

• Staff competence & training files

• Equipment maintenance logs

Proper documentation demonstrates compliance and is essential during NABL assessments.

Common Mistakes to Avoid

❌ Buying incorrect weight class

❌ Believing full-capacity weights are mandatory

❌ Using customer material without proper substitution method

❌ Missing environmental monitoring

❌ Poor uncertainty calculations

❌ Incomplete documentation

Avoiding these ensures smooth NABL audits.

How V-CARE IMPEX Supports NABL-Ready Labs

V-CARE IMPEX offers:

• E1, E2, F1, F2, M1 Standard Weights

• Full fractional sets for analytical & micro balances

• 20 kg stainless steel weights for platform scales

• NABL-traceable calibration certificates

• Trolleys, boxes, weight racks & accessories

• Consulting support for choosing weights and methods

• Complete weight kits for NABL start-up labs

Our products are used by leading NABL labs across India, Middle East & Asia.

Conclusion

Understanding the NABL requirements for calibration of weights and balances makes the accreditation process simple and manageable. With the correct standard weights, scientifically accepted methods, complete documentation and proper environmental controls, any lab can confidently achieve NABL accreditation.

Whether you are calibrating microbalances, analytical balances, or high-capacity platform scales, the right combination of weights and methods ensures compliance and accuracy.

For trusted standard weights and NABL guidance, V-CARE IMPEX is your reliable partner.

📌 Disclaimer

The information provided in this blog is based on general industry practices, publicly available NABL guidelines, and professional experience. It is intended solely for educational and informational purposes.This content should NOT be treated as an official, complete or final reference (“not a bible”) for NABL accreditation.

NABL requirements may change from time to time, and actual assessments may vary depending on:

• The assessor’s judgment

• Your laboratory’s scope

• Equipment condition

• Documentation quality

• Uncertainty budget

• Current NABL policy/updates

Readers are strongly advised to:

👉 Verify all technical requirements directly from NABL documents (NABL-100, NABL-102, NABL-141, ISO/IEC 17025:2017) and relevant OIML standards.

👉 Consult a qualified NABL consultant or assessor before making investments or scope decisions.

V-CARE IMPEX is not liable for any decisions, actions, or interpretations made solely based on this blog.