Foundations
Milligrams vs. millilitres
Two units that measure different things but sit next to each other in every calculation on the site.
- Last updated:
- 2026-07-22
Overview
Milligrams (mg) measure mass — how much peptide is present. Millilitres (mL) measure volume — how much liquid occupies a space. The two are related by concentration (mass per volume), but they are not the same kind of quantity.
Every compound page uses both. Reported research amounts are in mg or mcg; reconstituted volumes and syringe draws are in mL (or in insulin-syringe units, which represent hundredths of a mL).
Why it matters
Reading "0.25" without knowing whether it means milligrams or millilitres is meaningless. "0.25 mg" and "0.25 mL" can differ by a hundredfold or a thousandfold in what they represent.
Key concepts
1 mL = 1 cm³
A millilitre is a unit of volume equal to one cubic centimetre. For dilute aqueous peptide solutions, 1 mL of solution weighs approximately 1 gram, but the mass of the dissolved peptide inside it is not 1 gram; it is whatever the concentration says.
1 mg = 1 000 mcg
A milligram is a thousand micrograms. Reported research amounts in this field appear in both units. A protocol expressed in mcg is not smaller than a protocol expressed in mg; it is the same kind of quantity written more precisely.
Concentration is the bridge
The unit that turns mg into mL is mg/mL (or mcg/mL). Multiply an mg amount by mL/mg (the inverse of concentration) to get mL.
Common misconceptions
- "0.5 mL" is not "half a dose." It is half a millilitre of whatever the current concentration is; the mass of peptide depends on the concentration.
- Increasing volume does not increase the amount of peptide. Injecting more mL of the same solution injects more peptide; injecting the same mL of a different concentration injects a different amount.
- Insulin-syringe units are not micrograms. A U-100 insulin syringe reads in hundredths of a mL, not in mcg. The mass a unit represents depends on the concentration.
Practical interpretation
When you write down a dose, write down both the mass (in mg or mcg) and the volume (in mL or units). Either alone is ambiguous.
Limitations
Locale formatting differs: English uses "2.5 mg/mL" and Spanish uses "2,5 mg/mL" for the same value. The comma-versus-decimal convention is presentational only; the underlying number is the same.