Mass: g, mg, mcg
The metric mass ladder steps by a thousand at each rung. A gram is 1,000 milligrams; a milligram is 1,000 micrograms. Peptide vials are labelled in milligrams because the powder is weighed at that scale, while published regimens are often expressed in micrograms because the amounts studied are small. Moving between the two is a matter of shifting the decimal point three places, and getting the direction wrong is the most common arithmetic error in this field.
You will see micrograms written three ways: µg, ug and mcg. They are identical. Clinical style guides prefer mcg because a handwritten or badly rendered µ looks like an m, and “mg” is a thousand times larger.
Volume: mL and insulin units
An insulin syringe is a volume-measuring device with a scale printed in units rather than millilitres. On the U-100 scale, which is standard in the United States, 100 units occupy exactly 1 mL, so one unit is 0.01 mL. The name comes from insulin, which is formulated at 100 units per millilitre; the syringe scale carries over to any liquid, but the units only ever describe volume.
International units
An IU is not a mass. It is an amount of biological activity, defined for a single substance by comparison with a reference standard kept by the World Health Organization or a pharmacopoeia. Because the standard is specific to the substance, there is no universal IU-to-milligram factor, and applying one substance's factor to another produces a meaningless number.
The only compound on this site with a widely cited standard is somatropin, recombinant human growth hormone, for which 1 mg corresponds to 3 IU. Research peptides such as BPC-157, TB-500 or CJC-1295 have no IU definition; products that quote them in IU are using a private convention, and this converter returns an explicit error rather than guessing.
Conversions that go wrong
- Reading a 0.25 mg entry as 25 mg, or 250 mcg as 250 mg, by dropping the decimal or the prefix.
- Assuming 10 units on a syringe means 10 of anything other than hundredths of a millilitre.
- Using a U-40 or U-50 syringe with U-100 arithmetic. The scale is printed on the barrel.
- Treating an IU figure from one substance as if it applied to another.
Related
- Reconstitution calculator for vial + water + amount arithmetic with a syringe diagram.
- Guides on what peptides are, how reconstitution is done in the literature, and what the regulatory status of each compound means.
Frequently asked questions
How many mcg are in 1 mg?
1,000. A milligram is one thousandth of a gram; a microgram is one millionth. Vial labels are usually in mg and study regimens are often in mcg, so most conversions on this page are a factor of a thousand.
How many units are in 1 mL?
On a U-100 insulin syringe, 100 units equal 1 mL, so 1 unit is 0.01 mL. Other syringe scales exist (U-40, U-50) but U-100 is the standard in the United States.
Can I convert mg to mL?
Not directly. Milligrams measure mass and millilitres measure volume. The link between them is concentration, which depends on how much liquid the powder was dissolved in. The reconstitution calculator does that conversion once you enter the vial size and water volume.
What is an IU and why is there no general IU-to-mg factor?
An international unit measures biological activity against a reference standard defined for one specific substance. The factor is different for every substance, and most research peptides have no standard at all. This converter only offers IU for somatropin (human growth hormone), where the World Health Organization standard sets 1 mg equal to 3 IU.
Is µg the same as mcg?
Yes. µg, ug and mcg all mean microgram. Mcg is preferred in clinical writing because the Greek letter mu is easily misread as an m, which would turn micrograms into milligrams.