Glossary
Micrograms vs Milligrams
One milligram equals 1,000 micrograms. Why vials are labelled in mg while research reports use mcg, and where the factor-of-1000 mistake slips in.
A milligram (mg) is a thousandth of a gram, and a microgram (mcg or µg) is a millionth. The conversion never changes: 1 mg = 1,000 mcg, and 0.001 mg = 1 mcg. Peptide vials carry milligram labels because that is the sensible unit for weighing freeze-dried solids, whereas amounts in published studies and at receptor level are generally given in micrograms or nanograms.
Where the mistakes happen
Errors arise in the step from the label unit to the working unit, and misplacing a decimal point here is a thousand-fold mistake, not a tenfold one. Consider an example: a 5 mg vial reconstituted with 2 mL of bacteriostatic water gives 2.5 mg/mL, equivalent to 2,500 mcg/mL. Draw 0.1 mL — ten marks on a U-100 syringe — and that volume holds 250 mcg.
Two habits lower the risk. Do the conversion a single time, when you calculate the reconstitution, and note the answer in both units on the vial label. And on handwritten labels write “mcg” rather than “µg”, because a rushed µ is easily read as m. The reconstitution maths guide and our unit converter walk through the arithmetic.
Related terms
molarity · molecular weight · reconstitution calculator