FreePeptideCalc

IU to mg Conversion — HGH, Insulin, HCG and Vitamins

Written by , who builds and maintains this site and is not a clinician. Every figure links to its primary source.

There is no universal IU to mg factor. An international unit is defined separately for each substance against its own reference standard. 1 IU of vitamin D weighs 0.025 mcg; 1 IU of somatropin weighs about 333 mcg. Any converter that gives one number without asking which substance is wrong for most of them.

IU to mg factors that actually exist

Each factor below is taken from the standard or label that defines it.

SubstanceFactor
Somatropin (HGH)1 mg = 3.0 IUWHO 2nd International Standard. 1 IU is about 0.333 mg.
Human insulin1 IU = 0.0347 mgSpecific activity of pure insulin, about 28.8 IU per mg, used with the WHO 2nd International Standard. The 1st standard defined 1 IU as 0.03846 mg of that hydrated crystalline material.
hCG, recombinant (choriogonadotropin alfa)250 mcg ≈ 6,500 IUAs stated on the EU Ovitrelle label — about 26 IU per mcg. The US Ovidrel label is dosed in micrograms only.
hCG, urinary (Pregnyl, Novarel)No mass factorLabelled in USP units of biological activity only. No milligram content is stated, so no conversion exists.
Vitamin D1 mcg = 40 IUHolds for vitamin D2 and D3.
Vitamin E1 mg = 1.49 IU (natural) or 2.22 IU (synthetic)Natural d-alpha-tocopherol versus synthetic dl-alpha-tocopherol. Same milligrams, different IU.
BPC-157, TB-500 and other research peptidesNo IU existsNo international standard has been established, so an IU figure for these is meaningless.

HGH IU to mg

mg = IU ÷ 3. This is the one peptide with an official factor; the HGH calculator then turns milligrams into syringe units for your cartridge.

IUmg
1 IU0.33 mg
2 IU0.67 mg
3 IU1 mg
4 IU1.33 mg
5 IU1.67 mg
10 IU3.33 mg
15 IU5 mg
36 IU12 mg

Vitamin D mcg to IU

IU = mcg × 40.

mcgIU
10 mcg400 IU
25 mcg1,000 IU
50 mcg2,000 IU
100 mcg4,000 IU
125 mcg5,000 IU
250 mcg10,000 IU
1250 mcg50,000 IU

IU, insulin units and syringe units are three different things

IU measures a drug’s activity. Insulin “units” are IU of insulin. The marks on an insulin syringe are volume — on a U-100 barrel, one mark is 0.01 mL. They agree only for U-100 insulin, which is made at exactly 100 units per mL. For anything else in that syringe, the marks tell you millilitres and nothing about IU. Use mL to units for the syringe and mg to units for a milligram-labelled vial.

Common questions

Sources

Every number on this page comes from one of the documents below. Where no reliable source exists, the page says so instead of filling the gap.

  1. ReferenceWHO / NIBSC· 2001
    WHO 2nd International Standard for Somatropin (NIBSC code 98/574) — 3.0 IU per mg
  2. GuidelineNIBSC / WHO Expert Committee on Biological Standardization· 2025-10
    2nd WHO International Standard for insulin, human (NIBSC 11/212) — Instructions for Use, mass assignment and specific activity
  3. GuidelineNIBSC / WHO Expert Committee on Biological Standardization· 2010-09
    WHO International Standard, Insulin, Human (NIBSC 83/500) — Instructions for Use, unitage definition
  4. FDA labelEuropean Medicines Agency
    Ovitrelle (choriogonadotropin alfa) — EU Summary of Product Characteristics
  5. FDA labelFDA / DailyMed· 2023
    PREGNYL (chorionic gonadotropin for injection, USP) — FDA prescribing information
  6. ReferenceNIH Office of Dietary Supplements
    Vitamin D — Fact Sheet for Health Professionals
  7. ReferenceNIH Office of Dietary Supplements
    Vitamin E — Fact Sheet for Health Professionals