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)
For powders, if you need the exact weight in the bottle, please request “Gross/Net/Tare weights” and we will actually put that information on the vial label so that you will know the exact amount in the vial. We do not charge extra for this service, but it must be requested at the time you place the order. Please communicate special packaging request when placing the order, as customer service will be familiar with this type of inquiry.