How Does IU Compare To Mg? And Tips To Getting Healthier With Or Without Supplementation

Health is the greatest gift, contentment the greatest wealth, faithfulness the best relationship.
~ Buddha

We often find that IU and mg are used most often in medications and vitamins. As such some of you might be wondering why some vitamins are measured in IU or International Units and other vitamins and minerals are measured in mg or milligrams.

That’s a good question and will be the focus as we look at how does IU compare to mg in today’s post.

Milligrams put simply are just a measure of weight or mass and as such they don’t change based on the substance being measured or weighed. For example, 5 milligrams of Vitamin C and 5 milligrams of onion weigh the exact same amount.

This might seem obvious, as a milligram is one thousandth of a gram, or one millionth of a kilogram.

However, this is not the case with IU or International Units, IU is a measure of the bioactivity of a substance in the body. IU is used often in pharmacology and in medicine to measure biologically active substances such as some vitamins, hormones, vaccines, blood products and some medications.

Because some biologically active substances come in different forms, the idea behind IU is to be able to assess the effectiveness of the dose of a substance regardless of its form as a single measurement.

So for example 1 IU of vitamin A from either retinol or beta carotene should have the same biological effect on the body.

It is a little more complicated than a simple measurement of mass like the mg, especially for vitamins and minerals and as such more and more scientists are now measuring vitamins in mgs instead of IUs. It makes it easier for us as the consumer.

So if you are interested in converting from milligrams (mgs) to International Units (IUs) it is not a simple formula as each substance being converted requires a different formula of equation because IUs are based on biological activity and not mass.

In the case of vitamins, the most common vitamins offered in IUs instead of mgs are vitamins A, D and E though you can convert vitamins B and C from mgs into IUs if you want or need to.

To convert IUs of vitamin A to mgs or often into micrograms (mcgs) you multiply each 1 IU of retinol by 0.3 to get the number of mcgs. If you want to find out the amount of milligrams from your newly discovered mcgs you multiply by 0.001. If your vitamin A comes from beta carotene then you multiply each 1 IU by 0.6 mcgs to get the number of mcgs of beta carotene equivalent.

Vitamin D is easier. Vitamin D only has one way to convert from IU to mgs. You take 1 IU of vitamin D (cholecalciferol or ergocalciferol) multiply by 0.025 mcgs.

For vitamin E things get a bit more complicated as with vitamin A. Take 1 IU of vitamin E as d-alpha-tocopherol and multiply by 0.667 mgs to get the milligram equivalent. If your vitamin E is dl-alpha-tocopherol acetate then it is a 1:1 conversion i.e. 1 IU of vitamin E as dl-alpha-tocopherol acetate is equivalent to 1 mg of the same vitamin D.

More info than you perhaps wanted to know, but interesting nonetheless.

At the end of the day, to be healthy I don’t recommend getting your vitamins from supplements but rather from a whole foods plant based diet. On such a diet, the only vitamin you MUST supplement with is vitamin B12 as cyanocobalamin or methylcobalamin at a dose of 2,500 mcgs once a week or a daily 250 mcgs. I recommend this one which only costs pennies per week. Additionally you might want to take a seaweed based omega 3 supplement on a daily basis like this one here and perhaps a daily dose of around 2,000 IU (50 mcgs) vitamin D like these cheap pills. This is important if you live north or south of 30° latitude especially in the winter months.

Other than that, your whole and natural foods will provide you with just about everything you need. And the ones recommended above can be had on the cheap. Living lightly, healthily and in abundance is often cheaper than chasing false dreams.


  1. Can you tell me the conversion ratio between IU and mg for Beta Sitosterol? Thank you. Mike

  2. Sorry Mike,

    I don’t know the answer to that. Nor have I been able to research an answer for you. You might want to speak with your pharmacist or physician about that.

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