Reconstitution and dose-volume calculator
Bacteriostatic-water volume to concentration, dose to volume, and volume to insulin-syringe units — with the arithmetic shown rather than hidden.
Every figure here is derived from the label claim. That is the number printed on the vial, and this index exists partly because it is frequently not the number in the vial: the median recovery against label claim across 6,722 records is 98.1 %, and the 10th percentile is 90.3 %. To work from what is actually there, take the recovered-mass figure from a report on your lot and use it in place of the claim — the purity-to-mass calculator produces it.
The arithmetic
concentration (mg/mL) = label claim (mg) ÷ diluent volume (mL) concentration (µg/mL) = concentration (mg/mL) × 1000 volume for dose (mL) = dose (µg) ÷ concentration (µg/mL) syringe units = volume (mL) × units per mL on the barrel doses per vial = diluent volume (mL) ÷ volume per dose (mL)
None of this is difficult and all of it is routinely got wrong in one specific way: an insulin syringe is graduated in units, which are a volume marking tied to the U-100 insulin standard, not a mass. On a U-100 barrel, one unit is 0.01 mL. What that 0.01 mL contains depends entirely on how the vial was reconstituted, so "20 units" is not a dose and cannot be transferred between two differently-reconstituted vials.
What this calculator assumes and cannot know
- That the vial contains the mass on the label. It very often does not. Water, counter-ion and residual solvent all occupy cake mass, and purity below 100 % means some of the peptide present is not the target compound.
- That the diluent volume was accurate. A 2 mL draw from a bacteriostatic-water vial with a 30-gauge needle is not a volumetric measurement.
- That the material dissolved completely. Undissolved material lowers the delivered concentration and no arithmetic detects it. 5,805 records in this index report incomplete reconstitution.