To ensure we meet the minimum packaging requirements, we may over-pack our catalog products up to at least 10% (especially when dealing small unit sizes < 100 mg). Weights are determined by either physically weighting out (powders) or from measured aliquots from a gravimetrically determined solution and these are typically within 10%. For example, the concentration on the vial is correct (e.g. 5 mg/mL, 10 mg/mL, etc.), however you will receive a volume greater than required (e.g. for 1 ml solution perhaps 1.1 to 1.3 mL)