How the conversions work
Mass units step by a factor of 1,000: 1 g = 1,000 mg, 1 mg = 1,000 mcg and 1 mcg = 1,000 ng. Most peptide vials are labeled in milligrams, while research amounts are often discussed in micrograms, which is where most slips happen. Our guide to mg, mcg and IU conversion works through examples.
Volume to syringe units is a single multiplication: units = volume in mL × units per mL. A U-100 syringe has 100 units per mL and a U-40 syringe has 40, so the same volume gives a different number on each. See U-40 vs U-100 syringes for why that matters.
How to convert IU to mg
An international unit (IU) measures biological activity against a reference standard, not mass. Each substance has its own standard, so 1 IU of one substance is not the same mass as 1 IU of another. The formula is mg = IU ÷ (IU per mg). The presets use the NIH Office of Dietary Supplements factors for vitamins D, E and A and the WHO standard for somatropin (3 IU per mg). For anything else, enter the factor stated for your substance, or measure by mass where no IU standard exists. The IU to mg conversion guide has tables and sources.
To go from a vial and a volume of water to a concentration, use the peptide reconstitution calculator.
Frequently asked questions
How many mcg are in 1 mg?
1 mg equals 1,000 mcg (micrograms). To convert mg to mcg, multiply by 1,000; to convert mcg to mg, divide by 1,000. A 5 mg vial therefore holds 5,000 mcg.
How many units is 0.1 mL?
0.1 mL is 10 units on a U-100 syringe and 4 units on a U-40 syringe. Units depend on the syringe scale, so check the scale printed on the barrel.
How do I convert IU to mg?
Divide the IU amount by the substance's factor in IU per mg: mg = IU ÷ (IU per mg). Choose a preset (somatropin, vitamin D, E or A) or enter your own factor, and set the direction to IU to mg. For vitamin D, 1 mcg = 40 IU, so 1,000 IU is 25 mcg.
Can you convert IU to mg for any peptide?
No. An international unit is defined separately for each substance by a WHO reference standard, so each substance has its own factor. For somatropin the current standard is about 3 IU per mg. Most research peptides have no IU definition at all and are measured by mass.
Is this converter medical advice?
No. It converts units only. It does not know what any compound is or whether it is appropriate for any purpose.
More free tools
- Peptide reconstitution calculator (U-100 and U-40)
- BAC water calculator
- Peptide unit converter (mg, mcg, IU, mL and units)
- COA checklist
- Vendor testing tracker
Choosing a supplier? See the best peptide vendors in the USA.