USP <41> - Weights and Balances

What it says

Balances used for pharmaceutical testing and manufacturing must be selected with a minimum weighing capacity appropriate to the required accuracy, and routinely calibrated and performance-checked using weights that are themselves traceable and periodically verified.

Paraphrased for plain-language clarity. Always verify against the current published regulation text.

What it means in practice

• This chapter's minimum weighable quantity concept means a balance is not simply accurate or inaccurate in the abstract, it has a defined lower limit below which a weighing result cannot be trusted, and using it below that limit is itself a quality risk.
• Because so much of pharmaceutical testing and formulation depends on accurate weighing, an unqualified or out-of-tolerance balance can introduce error that propagates silently through everything from raw material weighing to finished product testing.
• Reference weights used to check a balance's performance must themselves be traceable and periodically verified, meaning the calibration chain extends beyond the balance itself to the weights used to test it.

What inspectors look for

• Whether balances in use have a documented minimum weighable quantity and whether actual weighings performed stay above that limit.
• Whether routine balance performance checks and calibrations are being performed on schedule using traceable reference weights.
• Whether an out-of-tolerance balance finding triggers an assessment of which prior test results or batch weighings may have been affected.

Related regulations