One milligram is 1,000 micrograms, and micrograms are written mcg or µg interchangeably. International units are different: IU is not a mass unit and needs a compound-specific factor. Syringe units need a concentration. This converter handles all three.
A math tool, not medical advice.
This calculator only does arithmetic on the numbers you type. It does not recommend a dose, a schedule, a compound, or a supplier. Most peptides are not FDA-approved and many have no legal supervised route at all. Check how we grade the evidence and talk to a licensed clinician.
Micrograms are written mcg or µg. They are the same thing.
IU/mg
IU is not a mass unit. Each substance has its own IU definition set against a biological reference standard, so this factor must come from that compound's documentation. We do not assume one.
mg/ml
Needed to turn a mass into a volume or into syringe units. Get it from the reconstitution calculator if you're mixing a vial.
The math
Enter an amount to convert across the mass scale. Add an IU factor or a concentration to convert into international units or syringe units.
Conversion only. Nothing here is a dose, and a number being easy to draw up says nothing about whether it is appropriate or safe.
The mass scale: mg, mcg and ng
These are straightforward multiples of a thousand. Vials are usually labelled in milligrams while protocols are usually quoted in micrograms, so a 5 mg vial contains 5,000 mcg. Getting this wrong by a factor of 1,000 is the single most common peptide arithmetic error, and it runs in the dangerous direction.
Why IU cannot be converted without a factor
An international unit measures biological activity, not weight. The amount of substance that constitutes one IU is set separately for each compound by international reference standards, which is why there is no universal mg-to-IU number. Any calculator that converts mg to IU without asking which compound you mean is guessing. Take the factor from the product documentation or the compound's label.
Syringe units depend on your concentration
A U-100 insulin syringe is marked in 100 units per millilitre, so a unit is a measure of volume (0.01 ml), not of mass. The same dose is a different number of units at every concentration, which is why reconstituting the same vial with a different amount of water changes the number on the syringe without changing the dose. If you are mixing a vial, get the concentration from the reconstitution calculator first.
FAQ
Frequently asked questions
How many mcg are in a mg?+
1,000. One milligram equals 1,000 micrograms, and one microgram equals 1,000 nanograms. Micrograms are written either mcg or µg, and the two mean exactly the same thing. Most peptide doses are quoted in mcg while vials are labelled in mg, which is where the confusion usually starts.
How do you convert mg to IU for a peptide?+
You cannot, without knowing that specific compound's conversion factor. IU is not a unit of mass. It is defined per substance against a biological reference standard, so the mg-to-IU factor differs for every compound and has to come from that compound's own documentation. This converter asks you for the factor rather than assuming one.
How many units is 250 mcg on an insulin syringe?+
It depends on the concentration of your solution, not on the dose alone. A U-100 insulin syringe holds 100 units per millilitre, so one unit is 0.01 ml. At 2.5 mg/ml, 250 mcg occupies 0.1 ml, which is 10 units. At 5 mg/ml the same 250 mcg is 0.05 ml, or 5 units. Enter your concentration above.
What is the difference between mcg and µg?+
Nothing. They are two ways of writing microgram. The Greek letter mu (µ) is the formal symbol, and mcg is the written-out form preferred in clinical settings because µ can be misread on handwritten notes. Some vendors mix both on the same label.