How much is an International Unit?

by Monica Reinagel, MS, LDN on August 25, 2011

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 

{ 25 comments… read them below or add one }

ADOoOLA December 13, 2011 at 9:31 am

it’s useful, thank you very much. :-)


Baltimorekid August 9, 2012 at 2:20 pm

Thank you very much , learning every day!


Luiza November 30, 2012 at 2:21 pm

Spectacular post, clear and simple, easy to understand! Just what I needed. Thanks.


Clay January 6, 2013 at 1:09 am

Ok so now how much is .3 mcg in I.U?


Monica Reinagel January 6, 2013 at 11:10 am

Clay, as I (tried to) explain above, it depends on the nutrient. 0.3mcg of WHAT?


jangra vicky May 7, 2013 at 6:06 am

seems u have asked for vit A i.e. 1 IU


Clay January 6, 2013 at 1:16 am

So are you saying 300 mg. is 300 IU?


David Olney January 23, 2013 at 6:40 pm

Any conversion for vitamin B-12 at 1000 IU to mcg?


Monica Reinagel, MS, LDN January 23, 2013 at 6:48 pm

I’ve never seen B-12 measured in International Units.


Chuck Schramm January 30, 2013 at 11:50 am

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?


Monica Reinagel January 30, 2013 at 5:22 pm

Check with him but I bet he meant to say mcg. 1000mcg is a fairly common dose of B12. I’ve never seen B12 given in I.U.s.


Yvonne Maynard March 25, 2013 at 2:04 am

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.


Yvonne Maynard March 25, 2013 at 2:26 am

I have just discovered that ug is not International Units. Sorry to waste your time.


PR April 29, 2013 at 4:58 am

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!


yvonne maynard April 30, 2013 at 12:16 am

Thank you very much PR, your information is very helpful.


Sagar April 1, 2013 at 3:27 pm

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


Genesis December 23, 2013 at 2:49 am

Please help to convert 10mg of vitamins E to MG? please advise me? really need to know


Genesis December 23, 2013 at 2:53 am

Correction… 10MG to IU? i want to know the right convertion please , from 10MG to IU? hoping someone to response on this msg. thank you


PR December 23, 2013 at 1:57 pm

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!


WhichOne March 16, 2014 at 12:37 pm

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.


mobile phones games April 5, 2014 at 3:23 am

That is a very good tip especially to those fresh to the blogosphere.
Simple but very precise info… Appreciate your sharing this one.
A must read post!


Eduardo Candido October 25, 2015 at 4:24 pm

How do I convert vitamin k ui in mcg?



Monica Reinagel, MS, LD/N October 26, 2015 at 6:36 am

International Units are not typically used for vitamin K. It is measured in micrograms (µg)


Wendy Round June 6, 2016 at 7:16 am

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.


Judy October 24, 2016 at 9:21 pm

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!


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