mcg to IU Converter

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Anna Szczepanek, PhD, Rijk de Wet and Aleksandra Zając, MD
Based on research by
Hewitt W. Theory and application of Microbiological Assay (December 1988)See 4 more sources
National Institutes of Health, Office of Dietary Supplements Dietary Supplement Ingredient Database - Unit Conversions (May 2016)WHO National Institute for Biological Standards and Control WHO International Standard OXYTOCIN 4th International Standard April 2013World Health Organisation WHO International Biological Reference Preparations (January 2016)WHO Expert Committee on Biological Standardization WHO International Collaborative Study of the Proposed 4th International Standard for Prolactin, Human (October 2016)
Last updated: Feb 02, 2023

Welcome to the mcg to IU converter — a painless way to turn the number of international units (IU) to either mcg (μg, micrograms), mg (milligrams) or g (grams) for a given substance.

Read on to discover some crucial facts about IU and learn how to convert IU to mg or other metric units.

💡 Just to remind you — all of our calculators work both ways! That's why it's just as easy to convert mcg to IU as IU to mg.

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment. If any health condition bothers you, consult a physician.

What is IU?

IU, the international unit, is a measure of biological activity of a given substance. The IU defines the effect, not the weight of a medium.

The IU value is established by an international agreement. It is different for every drug, blood product, vitamin, vaccine, or hormone. 💉

Why do we use IU?

The international unit (IU) can be usually spotted on packages of vitamin A, vitamin D, hCG or insulin.

Sometimes it is easier to express the effect of a substance needed than the weight of it. For instance., suppose we know the required activity. In that case, if two similar substances have exactly the same weight but different activities, we can still easily calculate how much of them we really need to fulfill our requirements.

💡 We offer a range of different vitamin calculations!
Start your journey with the vitamin A calculator or check whether you spend enough time in the sun using the vitamin D calculator.

Conversion from mcg to IU — how does it work?

Since International Units and metric weight units describe two entirely different qualities, we can't convert all the substances the same way. We need to know the exact value of IU per mcg that should be applied in a given situation.

Our mcg to IU converter comprises an extensive list of different compounds that can be translated into metric units and vice versa. They are all sorted in alphabetical order.

How to convert mcg to IU for vitamin A?

Let's translate mcg into IU using 3 simple steps:

  1. Find the conversion factor for vitamin A (retinol): 3.33 IU/mcg
  2. Make use of a simple formula: Amount in IU = Amount in mcg × 3.33 IU/mcg
  3. That's it! You're good to go.🎉

ps. You can simply turn IU to mg, by choosing the equation: Amount of mg = Amount of IU × 0.0003

How to convert 1500 IU to mcg for vitamin D?

Another easy, yet useful skill to acquire! We'll finish this task in no time.

  1. Find the conversion factor for vitamin D (cholecalciferol): 40 IU/mcg
  2. Try the equation: Amount in mcg = Amount in IU / 40
  3. Calculate! 1,500 IU / (40 IU/mcg) = 37.5 mcg
  4. Analyse the result: 1,500 IU of vitamin D activity can be found in 37.5 mcg of this substance.

How to convert 500 mcg to IU?

We can't answer this question if we don't know the exact conversion factor of a specific substance we'd like to convert.

  1. If we wanted to perform this calculation with, e.g., prolactin (a hormone that enables milk production), we'd need to use the value of 0.02094 IU/mcg.
  2. We'd use a simple equation: 500 mcg × 0.02094 IU/mcg = 10.47 mcg
  3. Voilà! It wasn't that hard, was it? 🤓
Łucja Zaborowska, MD, PhD candidate
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