How much iron is in one iron supplement?

December 20, 2025 •

6 min read

According to the NIH, the elemental iron content in supplements varies significantly depending on the form, with some common types like ferrous fumarate containing 33% elemental iron by weight while ferrous gluconate contains only 12%. Knowing how much iron is in one iron supplement is crucial for correct intake and avoiding adverse effects.

Quick Summary

The quantity of elemental iron per supplement dose varies widely by type and formulation. Common forms, such as ferrous sulfate and ferrous fumarate, contain different percentages of elemental iron. Supplement labels list elemental iron content, which is the key metric for accurate intake, and should be taken into consideration alongside other nutritional information.

Key Points

Elemental Iron is Key: Always check the 'Supplement Facts' panel for the elemental iron content, which is the actual amount of usable iron, not the total weight of the iron compound.
Content Varies by Form: Different iron compounds contain varying amounts of elemental iron; for example, a 325 mg ferrous sulfate tablet typically provides about 65 mg of elemental iron, while a 300 mg ferrous fumarate tablet offers around 99 mg.
Bioavailability Matters: Chelated iron forms, like bisglycinate, may have lower elemental iron content per pill but offer better tolerability and higher absorption.
Consult a Professional: Iron needs are highly individual, so a doctor can assess your bloodwork and discuss appropriate strategies to address deficiency safely.
Manage Absorption: To help optimize absorption, consider taking iron supplements separately from calcium, dairy, and caffeine, and potentially pairing them with vitamin C.
Mind the Upper Limit: The tolerable upper intake level (UL) for adults is 45 mg of elemental iron per day; exceeding this, especially without medical supervision, may lead to adverse effects.
Toxicity is a Risk: Overdosing on iron can be toxic and is particularly dangerous for children, which is why supplements should be stored securely.

The amount of elemental iron present in a single supplement can vary dramatically, a critical detail often overlooked by consumers. While a label may state a high milligram figure, this number typically refers to the weight of the iron compound (e.g., ferrous sulfate), not the actual amount of usable elemental iron your body absorbs. Understanding this difference is key to effective and safe supplementation.

The Difference Between Iron Compound and Elemental Iron

Most iron supplements contain iron in the form of a salt, such as ferrous sulfate or ferrous gluconate. These compounds consist of the elemental iron molecule bound to another substance. The total weight of the pill or capsule includes both the iron element and its bonding agent. The 'elemental iron' is the net amount of iron available for absorption by the body, and this is the number that matters for determining your actual intake. For example, a 325 mg tablet of hydrated ferrous sulfate contains about 64 mg of elemental iron, whereas a 325 mg desiccated ferrous sulfate tablet may contain as much as 120 mg of elemental iron. The best practice is to always check the 'Supplement Facts' panel on the product label, which is required to list the elemental iron content explicitly.

Common Types of Iron Supplements and Their Elemental Iron Content

The form of iron in a supplement affects its percentage of elemental iron. Here is a breakdown of some of the most common types and their typical elemental iron content:

Ferrous Sulfate: Often found in tablet or liquid form, it is one of the most common and cost-effective iron supplements. A standard 325 mg tablet of hydrated ferrous sulfate provides approximately 65 mg of elemental iron.
Ferrous Fumarate: This form offers a higher percentage of elemental iron by weight. A typical 300 mg tablet of ferrous fumarate contains around 99 mg of elemental iron.
Ferrous Gluconate: This option is less concentrated, with a 325 mg tablet providing about 39 mg of elemental iron. It is sometimes better tolerated by individuals who experience gastrointestinal side effects from other forms.
Iron Bisglycinate Chelate: This is a chelated form, where the iron is bound to amino acids, often glycine. Research suggests chelated iron may have increased bioavailability and fewer gastrointestinal side effects compared to non-chelated versions.

Factors Influencing Iron Needs

Determining individual iron needs is not a one-size-fits-all approach. Several factors must be considered, and it is always best to consult with a healthcare provider before starting supplementation.

Severity of Deficiency: Individuals with diagnosed iron deficiency anemia may require different levels of elemental iron compared to those taking a supplement for maintenance.
Diet: The type of iron consumed from food affects absorption. Heme iron from meat is generally more readily absorbed than non-heme iron from plant sources.
Life Stage: Recommended daily iron intake varies significantly by age, sex, and life stage, with pregnant women having higher requirements.
Absorption Inhibitors and Enhancers: Certain substances can interfere with iron absorption. Calcium supplements and foods like dairy products, tea, and coffee should ideally be consumed at different times than an iron supplement. Conversely, vitamin C can significantly enhance absorption.

Comparison of Iron Supplement Types


Feature	Ferrous Sulfate	Ferrous Fumarate	Ferrous Gluconate	Iron Bisglycinate Chelate
Cost	Generally lowest	Moderate	Moderate	Higher
Elemental Iron (%)	~20% (Hydrated)	~33%	~12%	Varies
Gastrointestinal Effects	More common	Moderate	Less common	Often very well-tolerated
Absorption	Good absorption, but can be hindered by diet	Good absorption	Good, but lower elemental content	High bioavailability, less affected by dietary factors
Ideal For	Addressing deficiency	General iron supplementation	Individuals sensitive to GI side effects	Chronic supplementation and sensitive stomachs

Conclusion: How to Choose the Right Supplement

The question of "how much iron is in one iron supplement?" does not have a single answer, as it depends on the specific compound used and its elemental iron content. Your primary focus should be on the elemental iron listed on the Supplement Facts panel. For addressing a deficiency, options like ferrous sulfate may be considered, while those with sensitive stomachs or needing long-term maintenance may prefer a chelated form with better tolerability. Always consult a healthcare provider to determine your personal iron needs and the most suitable supplement type. It is also important to consider the timing of your dose, potentially taking it on an empty stomach for maximum absorption or with food if you experience stomach upset. Exceeding the tolerable upper intake level (UL) for adults without medical supervision may lead to adverse effects.

This article is for informational purposes only and is not a substitute for medical advice. Please consult with a healthcare professional regarding any health concerns or before making any dietary changes. [Outbound link: https://ods.od.nih.gov/factsheets/Iron-Consumer/]

The Role of Elemental Iron in Supplement Selection

Selecting an iron supplement depends on understanding elemental iron, not just the total weight of the compound. Different forms, such as ferrous sulfate and ferrous fumarate, contain varying concentrations of usable iron. The body's absorption rate can be influenced by other dietary factors, such as the presence of vitamin C, which enhances absorption, or calcium and certain foods, which can inhibit it. Understanding individual iron status is crucial, as excessive intake can be toxic. Consulting a healthcare provider is essential to determine the appropriate approach for specific needs.

Risks of Excessive Iron Intake

Taking too much iron, especially from supplements, can lead to iron overload, which can be toxic. Side effects of high intake can include constipation, nausea, and abdominal pain. Extremely high levels can be dangerous, which is why supplements carry warning labels regarding accidental poisoning in children. Individuals with hereditary hemochromatosis, a genetic condition causing excessive iron absorption, should generally avoid iron supplements unless advised by a medical professional. Safe upper limits have been established for different age groups.

Optimizing Iron Absorption

To maximize the potential effectiveness of an iron supplement, timing and pairing with other nutrients are important. Taking iron on an empty stomach may improve absorption, but if this causes stomach upset, taking it with a small amount of food is an option. Combining iron with a source of vitamin C may enhance absorption. Conversely, consuming iron simultaneously with calcium, antacids, or products containing caffeine can decrease absorption and may be avoided.

Understanding Bioavailability in Iron Supplements

Bioavailability refers to the proportion of a nutrient that is absorbed and utilized by the body. While ferrous sulfate may contain a high percentage of elemental iron, some newer forms like iron bisglycinate chelate are designed for potentially higher bioavailability and better tolerability. The chelated structure is believed to potentially protect the iron from inhibitors in the gut, leading to more consistent absorption. This may involve a different elemental iron content but potentially more effective delivery to the body's iron stores over time.

Iron Supplements for Specific Populations

Certain groups have unique iron needs and considerations for supplementation. Pregnant women, for example, have a significantly higher iron requirement (27 mg per day), and supplementation is often recommended to help prevent deficiency. Infants, especially premature or low-birth-weight infants, may also require special consideration and supplementation under medical supervision. Frequent blood donors are at increased risk for iron deficiency and may need consideration for supplementation to help rebuild their iron stores.

The Importance of Professional Guidance

Given the complexity of iron requirements and the potential for toxicity, professional guidance is invaluable. A healthcare provider can assess your individual iron status through blood tests (e.g., serum ferritin) and determine if supplementation is necessary. They can discuss the most appropriate type of supplement based on your health, dietary habits, and any other medications you may be taking, helping you approach iron levels safely and effectively.

Frequently Asked Questions

The amount of elemental iron varies because supplements use different chemical forms of iron, such as ferrous sulfate, ferrous fumarate, or chelated iron. These compounds have different percentages of elemental iron by weight. The elemental iron content, which is the actual amount of usable iron, is the most important number to check on the label.

An iron supplement is made of an iron salt (a compound like ferrous sulfate) that includes both the iron mineral and other molecules. Elemental iron is just the pure iron mineral within that compound that your body can absorb. The total weight of the supplement is the iron salt, while the elemental iron is the amount listed on the Supplement Facts panel.

A standard 325 mg ferrous sulfate tablet contains approximately 65 mg of elemental iron. This is a common form used for iron supplementation, but the exact amount can differ based on whether the supplement is hydrated or desiccated ferrous sulfate.

Chelated iron supplements, like iron bisglycinate, are often associated with better tolerability and fewer gastrointestinal side effects compared to non-chelated forms like ferrous sulfate. While the elemental iron content per dose may be lower, the improved absorption and reduced side effects can potentially make them more suitable for some individuals, particularly for chronic supplementation.

Yes, it is possible to take too much iron, which can be toxic. In healthy adults, the Tolerable Upper Intake Level (UL) is 45 mg of elemental iron per day, unless advised otherwise by a doctor. High intake can cause side effects like constipation and nausea, and extremely high levels can lead to serious health problems or even death.

To potentially maximize absorption, consider taking your iron supplement on an empty stomach and with a source of vitamin C, such as orange juice. You may also want to avoid taking iron at the same time as calcium-rich foods or supplements, antacids, or caffeine, as these can inhibit absorption.

The best way to determine your specific iron needs is to consult a healthcare provider. They can perform blood tests to check your iron status and discuss appropriate strategies for supplementation based on your individual health, diet, and life stage.