Weighing Scale Calibration in Thailand: Legal Requirements, Procedure, and ISO 17025 Labs

Why Weighing Scale Calibration Matters — Both Legally and for Quality

Thai law (Weights and Measures Act B.E. 2542) requires all commercial weighing instruments to carry a Department of Internal Trade stamp and be inspected on schedule. Industrial scales used in food, pharmaceutical, and chemical production additionally require ISO 17025 calibration to satisfy GMP and ISO 9001 audits.

Scale Types and Their Requirements

• Analytical Balance (0.0001 g resolution) — Pharmaceutical dispensing, QC labs
• Precision Balance (0.001–0.1 g) — Food QC, chemical compounding
• Industrial Scale (kg–hundreds of kg) — Raw material receiving, production
• Checkweigher — Automated in-line underfill prevention
• Commercial Trade Scale — Legally mandated government stamp

Calibration Procedure

1. External inspection and leveling check
2. Zero/tare verification
3. Repeatability — 5–10 weighings of same calibrated weight
4. Eccentricity — weight placed at different positions on the pan
5. Linearity — multiple weights across full capacity
6. Error and uncertainty calculation per OIML R 76

OIML Weight Classes Required

Weight Class	Used to Calibrate
E1, E2	Analytical balances, reference standards
F1, F2	Precision balances, QC labs
M1, M2	Industrial scales, checkweighers

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