Peptide Units Glossary
A plain-language reference to every unit you meet in peptide research — mg, mcg, ml, syringe units, kDa and more — with the conversions that trip people up laid out clearly.
Peptide research runs on a small set of units, and almost every measuring error comes from confusing two of them — most often milligrams with micrograms, or millilitres with syringe units. Getting the vocabulary straight once removes a whole category of mistakes.
This glossary defines each unit in plain terms and gives the conversions that matter, so you can read a vial label, a calculator output and a syringe barrel without second-guessing. Keep it handy alongside the calculator and reconstitution-volume guides.
Research use only.
STEP-BY-STEP
Milligram (mg) — the vial mass
The milligram is how the total peptide in a vial is quoted — a "10 mg vial". It measures mass. One milligram is one-thousandth of a gram, and one thousand micrograms.
Tip: 1 mg = 1,000 mcg. This is the conversion behind most measuring confusion.
Microgram (mcg or µg) — the target measurement
Target research measurements are usually quoted in micrograms because they are small fractions of the vial. A microgram is one-millionth of a gram. To go from mg to mcg, multiply by 1,000; to go back, divide by 1,000.
Millilitre (ml) — the liquid volume
The millilitre measures liquid volume — how much bacteriostatic water you add, and how much solution you draw. One millilitre is one-thousandth of a litre. Reconstitution volumes are typically 1–3 ml.
Syringe unit — volume on a U-100 syringe
Insulin-syringe "units" are a volume scale, not a mass. On a U-100 syringe, 100 units = 1 ml, so 1 unit = 0.01 ml. Do not confuse a syringe unit with an International Unit — they are unrelated.
Tip: 1 ml = 100 units; 0.05 ml = 5 units. Units here mean volume, nothing about potency.
Concentration (mg/ml and mcg/ml)
Concentration is mass per volume — how much peptide sits in each millilitre of solution. It is set by your reconstitution: mass ÷ water volume. 10 mg in 2 ml is 5 mg/ml, equivalently 5,000 mcg/ml.
Molecular weight and the dalton (Da / kDa)
Molecular weight, quoted in daltons or kilodaltons (1 kDa = 1,000 Da), is the mass of one molecule of the peptide. It appears on Certificates of Analysis and is what mass spectrometry measures to confirm identity — not something you use for measuring draws.
The conversions worth memorising
Mass: 1 mg = 1,000 mcg. A 10 mg vial contains 10,000 mcg of peptide.
Volume on a U-100 syringe: 1 ml = 100 units; 0.1 ml = 10 units; 0.05 ml = 5 units; 0.02 ml = 2 units.
Concentration: mg/ml × 1,000 = mcg/ml. A 5 mg/ml solution is 5,000 mcg/ml.
A note on "IU": International Units are a potency-based measure used for some biological substances and are specific to each substance. They are not the same as insulin-syringe units (a volume scale) and cannot be converted to mass without a substance-specific factor. For the peptides discussed here, work in mg, mcg and ml.
PUT IT INTO PRACTICE
FREQUENTLY ASKED
How many micrograms are in a milligram?
One milligram equals 1,000 micrograms. So a 10 mg vial contains 10,000 mcg of peptide. Multiply mg by 1,000 to get mcg; divide mcg by 1,000 to get mg.
Are syringe units the same as millilitres?
No. On a U-100 insulin syringe, units are a volume scale where 100 units = 1 ml, so 1 unit = 0.01 ml. They are also unrelated to International Units, which are a potency measure.
What is the difference between a syringe unit and an International Unit (IU)?
A syringe unit is a volume marking on a U-100 syringe (1 unit = 0.01 ml). An International Unit is a potency-based measure specific to a given substance. They are completely different things and cannot be interchanged.
What is molecular weight used for?
Molecular weight (in daltons or kilodaltons) is the mass of one molecule, shown on a Certificate of Analysis. Mass spectrometry measures it to confirm the peptide's identity. It is not used for calculating draw volumes.