How much is an International Unit?

Q. Most nutrients seem to be measured in mg but some are shown as mcg or I.U.  How do I convert these measurements into mg?

A.  To convert micrograms (mcg) to milligrams (mg),  divide by 1,000–or move the decimal point 3 positions to the left.   1000 mcg = 1.000  mg.   But generally, you won’t need to convert between these two.  We use micrograms for nutrients that occur in very small amounts (folate, vitamin B12,  vitamin D, and vitamin K, for example).   Instead of writing that a food contains 0.125 mg of vitamin K, it’s less confusing to write that it contains 125 mcg.  You generally wouldn’t find milligram amounts of vitamin K in foods or supplements.

Converting International Units (I.U.) isn’t so simple–because it’s a different conversion for each nutrient.  The I.U. is an arbitrary amount based on the amount of a given nutrient needed to produce a biological effect.  Here are the conversions for the most common nutrients.

Nutrient Amount in 1 I.U.
Vitamin A 0.3 mcg
Beta-carotene 3.6 mcg
Vitamin D 0.025 mcg
Vitamin E 0.67 mg


For more tips on how to read nutrition facts labels and ingredient lists, check out this sample chapter from my book, Nutrition Diva’s Secrets for a Healthy Diet: What to Eat, What to Avoid, and What to Stop Worrying About 

38 thoughts on “How much is an International Unit?

      1. My doctor just suggested I take 1000 IU daily of vitamin B12 so I am also interested in the IU to MCG conversion for B12?

          1. My supplements are measured in IU (1000 IU). Can you provide th conversion rate to mcg? As all the resources I have on nutrition mention B12 in mcg and not IU.

  1. I bought a bottle of Blackmores B12 recently and found it was measured in 100 ug. I assume ug is international units. I would also like to know how much I am taking in mg as I don’t want to take too much.

    1. So, not sure if you’ve already found the info you were looking for, but for future reference (because it can get confusing to consumers) …”µg” actually refers to micrograms (” µ” with a tail on the front representing “micro” or .000001)…which is 1/1000th of a “mg” (milligram). Therefore 100ug B12 x 1/1000 = .1mg of B12 in your supplement.

      The National Institutes of Health recommends a daily allowance (RDA) of 2.4mcg ( another abreviation for microgram or “µg”) for females age 14+ per day; however oral B12 is notoriously not absorbed well by the body (especially unmethylated forms such as cyanocobalamine). Therefore, supplemental dosages are typically calculated to factor in excretion of b12 via bowel movements. You should speak with your primary care physician or clinical nutritionist in order to determine the best dosage for you though, because it really depends on your physical health, age, and/or if you have any existing conditions/diseases.

      But to dispel any angst…several adults are b12 deficient and are not aware although they consume the RDA of b12. In addition, b12 has low toxicity due to its water-solubility, so extra b12 naturally leaves the body via excrement.

      I know this is a lot of information for a simple question lol, but I do wish government health agencies would use more succinct methods of informing the general public about how to interpret what we are consuming. I could only imagine the discouragement many experience while attempting to decipher this info from any of the sources listed on the USDA website.

      If this information aids any others who read it, that was my intent. Hope that helps!

  2. Why is there IU? I don’t understand whats the reason!! So u saying 1 iu is .3 of A.. And .025 of D.. right? I have fracture.. I’m on a need to knw bases

    1. Only using the conversion factor at the top of this page because I don’t know the specific form of vitamin e you have…we multiply 10 IU by .67mg/1 IU because we want to cancel out the IU units. The result is 6.7mg of vitamin e. Hope that helps!

  3. In the IU/mg table in the article, you show Vitamin A, D, and E.

    If I understand how these things are named, each of those vitamins is actually a small set of chemicals (eg. D1, D2, D3, D4).
    Does an IU of D1 have the same mass-equivalent as an IU of D3?
    It’s important because it’s D3, in particular, that everybody’s taking megadoses of every winter…

    And, if Wikipedia is to be believed, there are well-characterized equivalents, relating the various “provitamin” A compounds to retinol:

    How much does that hold true for Vitamins D and E?
    And where can you go for an authoritative source?
    No list in the CRC Handbook last time I checked, but diet isn’t really their focus.

  4. Vitamin B12 is listed as “B12-25 ug” on my Asda “A-Z Multivitamins and Minerals” supplements. Folic Acid is also listed in “ug” on the bottle. Some other B vits are listed in mgs on the bottle. Asda in the UK is a very well used supermarket chain. I think it is the UK equivalent of the US Wallmart but would not want to swear to it. When buying separate B vits from other well known outlets and chemists they are very often listed in ugs. In the case of the Asda product the “u” has a curly tail. If you are trying to take certain quantities of B vits as decreed by a professional then it is very difficult to translate. Life is too short to calculate these measurements. I wish the industry would sing from the same hymn sheet. Even when you buy from health food shops it continues to be difficult.

  5. Hi there, I’m taking 5,000 iu of D3. For every 1,000 iu of D3 I’m supposed to take 100 iu of Vitamin K. I can’t seem to find a way to convert? I so appreciate any help you can provide!

  6. i too am being driven mad by search engines failing to take me to anywhere that lists both iu and mcg of vitamin Ks. no matter how i word it, i keep being brought back here. but the answer isnt here! really need to find out how to convert my menaquinones in both iu and mcg.

  7. Compound exercises will get the joint and muscle groups working at the same time. Forget isolation exercises like concentration curls. They only affect on joint your elbow and one muscle you bicep.

  8. So the original question of B12 mcg to IU was never answered. Just a stock generalized answer. So how many B12 mcg’s = how many IU’s.

    1. Vitamin B12 is not measured in International Units. It is measured in micrograms, which may be abbreviated as mcg or µg. Sometimes people confuse µg with IU.

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  10. The question still hasnt been answered! We r asking how many mcg of 12 is equivalent in iu. In aus its labelled as both!

      1. Vitamin B12 is not measured in International Units. Not in Australia nor anywhere else. It is measured in micrograms, which may be abbreviated as mcg or µg. Sometimes people confuse µg with IU.

        µg does not stand for international units. It stands for micrograms. So 12 µg = 12 micrograms.

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