How To Convert Between Different Forms Of Iron Supplements

We answer our latest question regarding the amount of elemental iron contained in over the counter iron supplements.


My Doctor wants me to take 325 mg iron supplement a day due to low iron blood test readings. I want to take Floradix Liquid Iron over the counter. How much do I take to equal 325 mg? Thank you!

Asked by Kev On Oct 03, 2017

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Oct 03, 2017
Iron Title


Getting the right dose of iron from your supplements can be surprisingly tricky. Unfortunately, most available over the counter iron supplements are not available as simply elemental iron. Iron is most often available only in a compound form, of which there are many (e.g. Ferrous Sulfate) and they each yield different amount of elemental iron.

Iron Supplements

The most common form of iron that doctors recommend is called Ferrous Sulfate and the most common dose recommended for patients is 325 milligrams. The confusing part is that doctors will often tell their patients to take "325 milligrams of iron" when in fact, 325 milligrams of a ferrous sulfate supplement yields only 65 mg of elemental iron!

This is because iron is just a component of the entire iron sulfate compound, FeSO4. We could get into the math, but most supplements will point this out on their label and state something along the lines of '325 mg ferrous sulfate' - '65 mg elemental iron'.

So it is extremely important to clarify how much elemental iron your doctor wants you to take. It most likely is 65 mg elemental iron (from 325 mg ferrous sulfate), but it's always a good idea to verify what they want.

As we mentioned, there are multiple iron compounds available for supplementation over the counter, and they each yield different amounts of elemental iron. Below are some of the common forms and conversion to elemental iron:

  • Ferrous Sulfate - Contains 20% elemental iron
  • Ferrous Gluconate - Contains 12% elemental iron
  • Ferrous Fumarate - Contains 33% elemental iron
  • Polysaccharide-iron complex - Contains 46% elemental iron
  • Ferrous bisglycinate chelate - Amounts vary on the formulation
  • Iron citrate - Amounts vary on the formulation

From the above chart of iron products, we can see that 325 mg of ferrous sulfate does indeed yield 65 mg elemental iron (i.e. 325 mg * 0.20 = 65 mg elemental iron)


Let's take a look at the product you mentioned in your question, Floradix.

There are multiple products of Floradix but the most common one contains 10 mg of elemental iron (from 83 mg ferrous gluconate). If your doctor wants you to take 65 mg of elemental iron (from 325 mg ferrous sulfate), you would need 6.5 servings of Floradix! This may not be a good idea as the product contains many additional vitamins/minerals and you may not want to get too much of those.

It is important to note that even supplements that provide the same amount of elemental iron may not necessarily be interchangeable.

For example, ferrous bisglycinate chelate is better absorbed than ferrous sulfate. Multiple studies have shown that ferrous bisglycinate chelate, even when given in the same elemental amount as ferrous sulfate, increases blood iron levels more than ferrous sulfate products.

Additional Information

Now, often times practitioners are okay with their patients taking different forms of iron in different amounts, as long as they are supplementing with something. They can always get a blood test at a later time and see if their levels are in the normal range. In general, studies show that hemoglobin levels can rise to normal levels regardless if you take low doses of iron or high doses.

Floradix also has the benefit of containing vitamin C which has been shown the improve absorption of iron and therefore enhances the effect of the supplement. Lastly, in my experience, iron can be very difficult to tolerate for patients as it often causes nausea.

Ferrous gluconate tends to be fairly well tolerated and in my opinion, causes less GI distress than high dose ferrous sulfate. Please check with your doctor and verify the amount of iron they want you to take and also verify if they are okay with you trying Floradix instead!

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Office: 716-389-3076

Recent Questions